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Essay Abstract

Current theoretical physics suggests the flow of time is an illusion: the entire universe just is, with no special meaning attached to the present time. This paper points out that this view, in essence represented by usual space-time diagrams, is based on time-reversible microphysical laws, which fail to capture essential features of the time-irreversible nature of decoherence and the quantum measurement process, as well as macro-physical behaviour and the development of emergent complex systems, including life, which exist in the real universe. When these are taken into account, the unchanging block universe view of spacetime is best replaced by an evolving block universe which extends as time evolves, with the potential of the future continually becoming the certainty of the past; spacetime itself evolves, as do the entities within it. However this time evolution is not related to any preferred surfaces in spacetime; rather it is associated with the evolution of proper time along families of world lines. The default state of fundamental physics should not be taken to be a time irreversible evolution of physical states: it is an ongoing irreversible development of time itself.

Author Bio

George Ellis is Professor Emeritus of applied mathematics at the University of Cape Town. He has written or co-authored many books and papers on relativity theory and cosmology, including On the Large Scale Structure of Space Time with Stephen Hawking.

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Dear Prof. Ellis,

It seems to me that, in order to talk about 'the flow of time', the past should not be sufficient to determine the present (cf. Conway-Kochen 'Strong Free Will Theorem', arXiv:0807.3286v1 [quant-ph]), and we have to consider the possibility that the Aristotelian 'final cause' may complement the relativistic causality, as elaborated here.

A penny for your thoughts!

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Dear Prof. Ellis,

Thank you for the beautiful and accurate picture of an Evolving Block Universe. I agree with you that the standard view of the block universe leaves to little room for the interesting phenomena occurring at higher levels. Please, consider that there may be two levels of the Physical World:

1. One of the possible solutions of the time evolution equation (forming a sheaf).

2. Another of the conditions, including an incomplete set of initial conditions, and “delayed initial conditions” caused by the quantum measurements.

It is possible to account for the quantum collapse without recurring to discontinuities, if we appeal to the entanglement of the system with the preparation device, and to the “delayed initial conditions”. At the level 1, the things happen deterministically, but there is a sheaf of such deterministic worlds. The level 2, containing the observers, and an incomplete set of initial conditions, can provide the evolution required. Being an incomplete set of constrains for the sections of the sheaf, it can be extended in multiple ways. There is room for the free-will, and the only uncertainty is provided by the yet-to-be-determined initial conditions. Our (temporal) choices allow us to select the section of the sheaf of solutions, in a non-local and trans-temporal way. I present briefly this idea in the section “Smooth Quantum Mechanics” in my essay, and in more detail in the attached document. Sorry for this intrusion, I wouldn’t dare if I haven’t thought that I can bring a small contribution to the Evolving Block Universe idea.

Cristi Stoica

“Flowing with a Frozen River”,

http://fqxi.org/community/forum/topic/322

attachments: smooth_qm.pdf

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Appreciated Prof. Ellis,

After reading your nice essay, I think that in mine I agree with you in most of your thougs but at a different level of argumentation.

I would be proud if you take a look at my essay Time Traveling by simuverses

Good luck in the contest.

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Dear George,

I'm sorry but your I have to stress that when you ask whether time is a macroscopic coarse grained phenomenon and you answer "No, because the quantum measurement process is not time reversible" unfortunately you make a common mistake.

You are not able to define the words "time reversible" and "time irreversible" if you don't implicitly use the notion of "time", so using the concept of "time reversibiltiy" when trying to saying something about the concept of time itself is a very obvious loop which implies that the consequent conclusions are wrong.

Obviously, since your work is based on this wrong argument, all the conclusions are probably wrong.

John

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Curious logic yours, Mr.John Smith. With a self made law about how to define thinks and a couple of sentences without conection you concludes that an entire job is not valid.

Be serious, please.

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Prof. Ellis, while I agree in general with your overall view of the evolution of the world, with determined past states and indeterminate future states described by quantum mechanics (QM), I disagree that the world lines of matter particles should be given primary importance. World lines are classical concepts that have no physical significance in QM, except as mathematical devices in e.g. path integrals. A continuous world line is not physically observable in QM, not even in principle, and not even for the past portion of world lines. What we can observe are at best discrete points on an imagined world line, which should not be taken as the primary concept in a theory of Becoming of the world. It seems that both in QM and General Relativity, 3-D space-like hypersurfaces are the best candidates to carry the world state at each moment of Becoming, thus they should be used as primary elements in a physical theory of Becoming of the world, at least in first approximation. But of course we then face the question of which space-like hypersurface to choose as the carrier of each moment of Becoming, as you pointed out, for which I don't have a definitive answer, though I did offer a toy model in my essay...

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Hello George!

Great essay!

You write, "This paper points out that this view, in essence represented by usual space-time diagrams, is based on time-reversible microphysical laws, which fail to capture essential features of the time-irreversible nature of decoherence and the quantum measurement process, as well as macro-physical behaviour and the development of emergent complex...

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Hello George!

Great essay!

You write, "This paper points out that this view, in essence represented by usual space-time diagrams, is based on time-reversible microphysical laws, which fail to capture essential features of the time-irreversible nature of decoherence and the quantum measurement process, as well as macro-physical behaviour and the development of emergent complex systems, including life, which exist in the real universe. When these are taken into account, the unchanging block universe view of spacetime is best replaced by an evolving block universe which extends as time evolves, with the potential of the future continually becoming the certainty of the past; spacetime itself evolves, as do the entities within it."

Space-time diagrams are a human constructs, that arise because people forgot that Einstein never stated that time is the fourth dimension, but rather he wrote x4=ict.

You would enjoy my paper! Time as an Emergent Phenomenon: Traveling Back to the Heroic Age of Physics by Elliot McGucken

"In his 1912 Manuscript on Relativity, Einstein never stated that time is the fourth dimension, but rather he wrote x4 = ict. The fourth dimension is not time, but ict. Despite this, prominent physicists have oft equated time and the fourth dimension, leading to un-resolvable paradoxes and confusion regarding time’s physical nature, as physicists mistakenly projected properties of the three spatial dimensions onto a time dimension, resulting in curious concepts including frozen time and block universes in which the past and future are omni-present, thusly denying free will, while implying the possibility of time travel into the past, which visitors from the future have yet to verify. Beginning with the postulate that time is an emergent phenomenon resulting from a fourth dimension expanding relative to the three spatial dimensions at the rate of c, diverse phenomena from relativity, quantum mechanics, and statistical mechanics are accounted for. Time dilation, the equivalence of mass and energy, nonlocality, wave-particle duality, and entropy are shown to arise from a common, deeper physical reality expressed with dx4/dt=ic. This postulate and equation, from which Einstein’s relativity is derived, presents a fundamental model accounting for the emergence of time, the constant velocity of light, the fact that the maximum velocity is c, and the fact that c is independent of the velocity of the source, as photons are but matter surfing a fourth expanding dimension. In general relativity, Einstein showed that the dimensions themselves could bend, curve, and move. The present theory extends this principle, postulating that the fourth dimension is moving independently of the three spatial dimensions, distributing locality and fathering time. This physical model underlies and accounts for time in quantum mechanics, relativity, and statistical mechanics, as well as entropy, the universe’s expansion, and time’s arrows."

http://fqxi.org/community/forum/topic/238

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Dear Dimi Chakalov

I have puzzled over the Conway-Kochen 'Strong Free Will Theorem' paper, without really understanding what if anything it has to do with free will [the wikipedia entry on the theorem is interesting in this regard]. However from the viewpoint of my own paper, that is not important: what matters is that their paper appears to reinforce the view that the outcome of quantum events is unknown until they happen. That is a key feature on which I build my proposal; so there is no conflict.

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Dear Cristi Stoica

thak you for the comments. I concur that your and my views may be regarded generally as in agreement; you elaborate the issues in interesting ways. A few comments: as to delayed measurement experiments, I agree with the view that you give in your paper: these experiments do not really measure the system, but rather its entanglement with the preparation device. The outcome is determined when the measurement is made, and is unknown and indeed unpredictable before then; this agrees with my view. I appreciate your emphasis on the preparation of the quantum system; this is the part of the whole package that is usually ignored, and which is just as mysterious as the measurement process. And finally you are concerned about free will in this overall context; please see, in this regard, my comments on causation in complex systems [the last reference in my posted paper]. I emphasise there the important role played by top down causation in the hierarchy of complexity, and of adaptive selection as a top down process. This does not solve the problem, but does indicate some ways whereby there can be a relaxtion of the iron grip of lower level causation.

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Dear Venerando

Your essay is very imaginative, and in some ways congruent to mine, but I find it diffcult to accept that "At the end, it will result on that, speaking about time travels, the virtual ones are more possible, more “real”, than the physical ones." In my own essay I have tried to carefully deal with only the real ones. And the very real problem with incredibly complex simulations such as those you (and others) envisage is that it is inconceivable they would run for more than a few microseconds without crashing. The task of designing them to actually work for a long time would be unfeasible. That is why biological systems do not work in an digitally-based algorithmic way; rather they work by adaptive selection.

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Dear John Smith,

you state `You are not able to define the words "time reversible" and "time irreversible" if you don't implicitly use the notion of "time", so using the concept of "time reversibiltiy" when trying to saying something about the concept of time itself is a very obvious loop which implies that the consequent conclusions are wrong.'

You can't talk about time at all without using the concept of time. My paper is based on how standard quantum theory in fact implies the flow of time in an ireversible way. This is one of the best tested theories in physics. If one is banned from using concepts such as time reversibility when talking about time, then no sensible discussion of the topic wil be possible. All the essays submitted to fqxi will be null and void.

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Dear Chi Ming Hung

the points you raise are interesting. One needs to discuss th eissue at the classical, semi-classical, and quantum gravity levels. I have focused on the first, where the use of timelike world lines is I believe valid. However at the quantum gravity level, one wants a full spacetime quantisation in my view (and as you suggest in your essay). Then my concept of development taking place point by point makesz sense. Still it would be interesting to develop further your proposal that "both in QM and General Relativity, 3-D space-like hypersurfaces are the best candidates to carry the world state at each moment of Becoming, thus they should be used as primary elements in a physical theory of Becoming of the world, at least in first approximation". It might be better in some contexts.

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Dear Dr. E (The Real McCoy)

I agree with the spirit of what you do in your essay, which as you point out is going in the same direction as mine. The main point where I differ is in the use of the imaginary time coordinate. I prefer to see it all done with a real time coordinate (see e.g. my book with Ruth Williams entitled "Flat and Curved Spacetimes"). So a key element is how proper time relates to coordinate time as we move to the future, which is what your key equation establishes; I think one can do this without introducing the imaginary quantity "i".

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I thought your paper was pretty interesting. I does seem to me that an evolving block universe is hard to make consistent with the concept of the block universe. We might think of the worldlines of particles or observers as having a fibration of spatial surfaces. Then a path integral of such world lines, on some base space of support, as related to each other by a fibration with an so(3)...

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I thought your paper was pretty interesting. I does seem to me that an evolving block universe is hard to make consistent with the concept of the block universe. We might think of the worldlines of particles or observers as having a fibration of spatial surfaces. Then a path integral of such world lines, on some base space of support, as related to each other by a fibration with an so(3) symmetry for spatial sheets.

The problem I see is how is it that time in general relativity and quantum mechanics can ever be made to agree with each other about time. In general relativity time is a symmetry of the theory, or in the su(1,1) part of the sl(2,C) group. One can in ADM relativity consider spatial surfaces as foliating a spacetime. How these spatial surfaces link together is chosen by the analyst in a manner similar to a gauge choice. This is of course curious, for we can think of time as some one dimensional space with a fibration given by spatial surfaces. So "choosing" how time acts is equivalent to choosing a section in a fibration of spatial surfaces.

Quantum mechanics in the other hand treats time as more concrete. The Schrodinger equation holds time as an evolutionary parameter which is not a symmetry of the Hamiltonian. In relativistic quantum theory one must assign fields on a spatial surface of simultaneity (equal time commutators of fields etc), and from there time acts as a parameter which fixes a Hamiltonian, but is not a symmetry of the Hamiltonian. Things get somewhat odd when the space or spacetime is curved. In particular the distinction between a vacuum and a particle state breaks down.

General relativity does not derive a Schrodinger equation per se, but in the "space plus time" ADM approach the canonical quantization of variables give HY[g] = 0. This Wheeler-DeWitt equation is then not a wave equation of evolution, but a constraint type of equation which specifies a wave functional on metric configuration variables.

This dichotomy between how general relativity and quantum mechanics treat time still obtains. The big theory of unification is string theory, which is more particle based based. There general relativity is treated with a background, which adulterates some aspect of gravitation. The other theory called Loop Quantum Gravity is more general relativity oriented, but this theory has difficulty in deriving particle or quantum physics in a workable manner. At the core of this problem is that GR and QM simply regard time in basically different ways.

In euclidean gravity time is related to a temperature as

t = hbar/kT

which indicates that on a microscopic level time is the phase description of spinor fields (or whatever substructure there is) to gravitation. There may then be a time, or equivalently a temperature, where the physics is scale invariant, which will occur for some very low temperature (T goes to zero) or equivalently a long time parameter. This is I think a quantum critical point, similar to the "breakdown" of electrons or quasi-particle Fermions in a Landau fluid.

Lawrence B. Crowell

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Dear Prof. Ellis,

Thank you for your kind comments. Also thank you for pointing me your article about causation in complex systems, I read it and found it very interesting. I agree with the view you presented there, and highly recommend it to everyone interested in causation.

Cristi Stoica

“Flowing with a Frozen River”,

http://fqxi.org/community/forum/topic/322

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Dear Professor Ellis,

In your reply to Elliot McGucken alias Dr.E (The real McCoy), essay 238, you denied the necessity of an imaginary time. Because my essay 369 claims having revealed improper interpretation of complex quantities, and I feel anyway obliged to react to some mistakes in several discussions, I suggest you might read my comment tomorrow there.

Sincerely, Dr.-Ing. Blumschein

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Dear Lawrence B. Crowell

thank you for your thoughtful comments. The problem lies in the interplay between spatial constraint equations and timelike evolution equations, the former being conserved by the latter. One needs to distinguish here between a generic formalism that applies in all circumstances, and a useful formalism that tells what happens in real world situations. In the recent universe on an astronomical scale it is only scalar perturbations that matter, with (in the zero-pressure case) characteristics that are timelike world lines. Spatial variation is a secondary consideration (one has what is called a `silent universe' where spatial derivatives can be neglected in the dyamical equations). In complex systems such as networks it is arrays of ordinary differential equations that best describe what is happening. How does that arise out of the underlying unification of quantum gravity and particle physics? So as well as the dichotomies you mention, there is the dichotomy between micro-physics and effective theories at macro scales. One can try to force the macro phyiscs to look more like the microphysics, which is in effect what happens when theoretical physicists suggest time is an illusion at the macro scale; or one can suggest the micro physical descriptions are missing some aspect that is apparent at the macro scale, which is in effect my suggestion here. In detail terms that means taking the measurement/collapse of the wave function issue seriously. Dealing with the Wheeler-de Witt equation alone, or any similar equation, won't suffice. The Hamiltonian development by itself is not the whole story.

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Dear Dr.-Ing. Blumschein,

I am not against complex numbers and complex functions in general; indeed Roger Penrose has a very nice discussion of their merits in his book The Road to Reality. I am against their use in the coordinates and/or space-time metric in General Relativity, except sometimes as complex conjugate pairs where they are a just shorthand way of descrbing two real quantities. The reason is that general coordinate transformations then become very difficult to handle, as they irretrievably mix up real and imaginary quantities, and what started off as a 4-dimensional spacetime begins to look like 8 an dimensional entity, but this is an illusion brought on by use of unsuitable notation.

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Thanks for the reply.

This makes me wonder if there is not some dualism of time. As a toy I might imagine the following. In four dimensions there is the dualism on chains 4 = m + n. We have the ADM model of spacial surfaces and a Hemiltonian defined on them so that HY[g] = 0. So there is a foliation of M^3 spaces, we choose a coordinate condition and then time is given according to the diffeomorphisms between these surfaces (laspe function etc). So this is what Wheeler called the many fingered time: you can push time in any direction you want, choose one and the "time" is a symmetry of the theory. We might then consider the dual of this approach. Suppose there exists a set of one dimensional spaces (lines or curves) These then have a fibration given by M^3 spaces, where one is free to choose any space possible at each point on a fibre. Pick a section in the fibre and local changes between coordinate on each line gives tranformations between M^3's.

So a theory of M^3 and you choose time, and a theory M^1 and you choose M^3. One is a constraint theory, the other a purely dynamical theory.

Something to ponder,

L. C.

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While the laws are time-reversible, the usually claimed time-symmetry of the microscopic world can be attributed to a misinterpretation of complex quantities explained in

http://fqxi.org/community/forum/topic/369

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Dear Professor Ellis,

Thank you for your reply. You are quite right. Nonetheless I do not share your aversion towards complex numbers. My point is:

Complex plane is in general assumed to contain much more data as compared to the real line. That's why quantum mechanics run into the trouble of Schroedinger's cat, entanglement, decoherence, etc.

If I am correct then only past time relative to any process of concern counts and analytical continuation just creates redundant data. Is there nobody who either refutes or supports this?

Sincerely, Eckard Blumschein

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Dear Prof. Ellis,

So far, I assume that Hilbert and his pupil J. v. Neumann were at least among the first who declared the flow of time an illusion. Do you know earlier ones?

Sincerely,

Eckard Blumschein

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Dear Eckard Blumschein

The idea is very much older than Hilbert. According to the Wikipedia article on Plato, "Plato, like so many other Greek philosphers, was stymied by the question of change in the physical world. Heraclitus had said that there is nothing certain or stable except the fact that things change, and Parmenides and the Eleatic philosophers claimed that all change, motion, and time was an illusion. Where was the truth? How can these two opposite positions be reconciled? Plato ingeniously combined the two" [in his theory of forms].

Sincerely

George Ellis

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Thank you for the reminder that toy models of reality are just that -- toys -- and that any theory which hopes to explain the real world must reflect that reality.

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Thanks for that, Tevian. I think your point is crucial: theoretical physicists tend to get totally caught up in their very simplified models of reality, and then start to confuse them with reality. We have attained a huge sucess in terms of our progress in fundamental physics (apart from the open question of quantum gravity). The problem now is to get a more realistic relation of this body of foundational theory to physical and biological reality, specifically the nature and functioning of truly complex systems. They too provide data about the nature of the real world; if necessary, the fundamental theories must be modified to take this data into account. And whatever one says about microphysics, it seems clear that the flow of time is not an illusion at the macro scale. I suggest, for example, that it is not yet determined who will win the fqxi essay prizes. This will be determined eventually, as part of the overall historical process, as the flow of time rolls inevitably on.

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Prof. Ellis: "I suggest, for example, that it is not yet determined who will win the fqxi essay prizes."

Perhaps also not after the prizes are awarded and you forgot who won?

About your essay, do you think that one can do experiments to find deviations of standard quantum mechanics, e.g. decoherence in isolated systems that are not due to interactions with the environment?

't Hooft has worked on models in which quantum mechanics is not fundamental. He is led to models in which information loss has to be present at the fundamental level, see e.g. here:

http://arxiv.org/abs/gr-qc/9903084

http://arxiv.org/abs/
hep-th/0105105

http://arxiv.org/abs/quant-ph/0212095

http://ar
xiv.org/abs/quant-ph/0604008

http://arxiv.org/abs/quant-ph/07
01097

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Dear Saibal Mitra

Your essay starts "Assuming the validity of the Many Worlds Interpretation of quantum mechanics (MWI), we examine the possibility of changing the past by memory erasure". I have problems with the many worlds assumption, as I have for example never had an answer from those I consulted as to how often the wave function branches, and what decides when it happens. I do not grasp the utility of the idea, which appears to be untestable. But maybe I will be persuaded some day. Your essay then carries on "In the future our descendents will probably be machines". I cannot concur with this assumption, indeed I am not sure that it makes sense. Then I cannot see any reality in your proposals about reloading and erasing memory: I do not believe this is remotely practicable. So I do not think there is any reality to the proposal that the identity of those who won the prizes can be altered after they have been won. I cannot see that this is a profitable line of speculation to pursue. However T'Hooft's ideas on quantum mechanics are surely worth consideration. Yes those kinds of experiments are certainly worth considering.

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Dear Prof. Ellis,

thanks for your comments. I'll write a detailed reply to your criticism on my essay on the comments page of my essay:

http://www.fqxi.org/community/forum/topic/354

to prevent the discussion here from going off topic.

I think the following points are appropriate to mention here:

1) It is legitimate to investigate the consequences of purely unitary time evolution. As of yet, there is no evidence that time evolution does not proceed in a unitary way. In my essay, I just considered a hypothetical (machine) observer who can erase his/her/its memory, I didn't speculate about new fundamental physics.

2) If it is proposed that time evolution is not unitary, then this has to be supported by experimental evidence. Because then a more complicated theory is proposed and, as of yet, it hasn't been shown that the purely unitary time evolution is not sufficient to account for all experimental data.

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Dear Professor Ellis,

Thank you for pointing me to Plato (427-348) and Aristoteles (384-322) who claimed: Numbers are basic to anything.

Ancient mathematicians did not have negative numbers. They certainly did not have the notion negative time.

After Descartes and Fourier necessarily obeyed the usual notion of what clocks putatively show, maybe, it was Minkowski who invented world-lines thought to range from minus infinity to plus infinity, Hilbert denied the arrow of time, and Einstein called the division between past and future an illusion. They all did so for mixed mathematical, religious, and speculative reasons, which are still dominating fund-raising including its reflection in the votes of this contest.

Mathematics claimed to generalize anything, and scientists are still considering most abstract and most general models as the deepest ones. Benefits for science, technology and economy seem to be more or less occasional spin-offs.

Regards,

Eckard Blumschein

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Dear Saibal Mitra

every time a quantum measurement is made the evolution does not proceed in a unitary way. Please see for example Roger Penrose: The Emperor's New Mind, pages 250-251, which makes explicit aspects of what is for example in Isham's book Lecturs on Quantum Theory, pages 71-73 and 82-85. You state "It is legitimate to investigate the consequences of purely unitary time evolution. As of yet, there is no evidence that time evolution does not proceed in a unitary way." You are talking of quantum theory without any measurements taking place, and hence no outcomes of any experiments and no evidence of anything. The many worlds picture does not change the abundant experimental proof that what we verify by experiment in the unverse domain we actually experience is measurements that proceed in a non-unitary way.

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Dear Prof. Ellis,

I think we would need evidence that a completely isolated system undergoes non unitary time evolution. If you are locked up in a hypthetically perfectly isolated box and you perform measurements in tat box then, if you are right, the wavefunction of the entire box would not evolve according to the unitary time evolution. Then, since you are a large collection of particles, one should expect that unitary time evolution is violated in general (apart form the, wavefunction collapse associated with measurements, which in the MWI is explained as the observer becoming entangled with the system).

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Dear Sabal Mitra

You say "I think we would need evidence that a completely isolated system undergoes non unitary time evolution." The whole point of my article is that there do not exist any completely isolated systems in the real world (except perhaps the universe itself). They are a fiction. The best you can do is partially isolate particular systems for limited times. But for example, the matter of which they are now composed was not isolated 14 billion years ago when they were part of the primeval soup. And the whole point about living systems is that they cannot function if isloated: they are open systems. The "hypothetically perfectly isolated box" you invoke is just that: hypothetical. It cannot exist in physical reality.

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Dear Prof. Ellis,

Yes, I agree with you here. I think 't Hooft also argued in a similar way in defense of his ideas. You have to assume that the fact that you cannot isolate a (macroscopic) system from the rest of the universe is (also) due to fundamental physics in such a way that assuming you could do so would lead to flawed conclusions.

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Suppose that quantum gravity is given by noncommutative geometries (plural) according to unitarily inequivalent groups. Further let there be associator maps between these groups. This would then be nonassociative QM, which is nonunitary. However, it can preserve quantum bits if described by E_8 or some sporadic group with an error correction capacity. A coarse grained description of this system, which eliminates nonassociative graphs, will then give a thermal description similar to Bogoliubov transformations used in black hole radiation.

This system might then be the entire universe, maybe more compactly described in it earliest fractions of femptoseconds of existence. Any supposedly closed system an experimenter might set up suffers from a number of problems. The system can't be kept completely away from the boundaries of the box, except for a black hole in the AdS spacetime. So there is no procedure for arriving at a perfect fine grained description for a system. Hence all systems we observe are ultimately open on some scale of frequencies, time or space.

Lawrence B. Crowell

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Dear Lawrence B. Crowell

thanks for that interesting elaboration.

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Dear George,

In response to my first posting from Dec. 2, 2008 @ 07:02 GMT above, on Dec. 3, 2008 @ 16:47 GMT, you wrote:

"... the outcome of quantum events is unknown until they happen. That is a key feature on which I build my proposal; so there is no conflict."

I'm glad to notice that you can surf the Web, so please check out the link to my essay 'Quantum Mechanics 101', in my first posting above. The crucial issue is *not* that the outcome of quantum events is "unknown until they happen".

We aren't talking epistemology here. The puzzle is know since 1935. To quote from Erwin Schrödinger's "Die gegenwärtige Situation in der Quantenmechanik":

"... measuring it does not mean ascertaining the value that it (the quantum system - D.C.) has."

As to whether there is conflict in your reasoning, I think it is too early to say anything conclusive. You haven't yet elaborated on the so-called Dynamic Dark Energy -- the driving force of 'the flow of time'.

I wish you best of luck in placing this perfectly smooth "dark stuff" on some Cauchy surface.

Dimi

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Dear Dimi Chakalov

you correctly note that my statement "... the outcome of quantum events is unknown until they happen. That is a key feature on which I build my proposal; so there is no conflict." is not as strong as it could be, and indeed should be. It must have been penned in haste, or late at night. I should have made it much stronger, as follows: "... the outcome of quantum events is unknown and indeed undetermined until they happen." Then I am no longer talking just epistemology: I am talking about the way things actually occur, as emphasized for example by Feynmann. This is what I in fact intended, amd is meant throughout my paper.

I have not related my paper to dark energy, as usually understood, because in my view that is a completely different puzzle from what is considered here. I do indeed have views on that issue, but see no reason to post them here.

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Dear George,

Good to see you (and your essay) here.

"The most important property of time is that it unfolds. The present is different from both the past and future, which in turn are completely different from each other, the past being fixed and the future changeable. The present is the instant of transition between these two states. The time that is the present at this instant will be in the past at the next instant."

I feel like I may be begginning to repeat myself a little in this essay contest, but it can be shown that if instants (and instantaneous magnitudes) existed, motion and change would be impossible. Furthermore, as instants would constitute the building blocks of time, if they can't/don't exist, neither can time.

"But one thing is clear: both the entire Darwinian process of evolution through which we come into existence, and the processes by which we read this article, depend on the flux of time. You would not exist and have the ability to read this article if the view proposed here (and expounded in more detail in Ref. [6]) was not a correct description of the way things are."

That's not the case. Indeed, it would only apply if instants (and time) did exist. I agree that it does apply to the standard interpretation of block time, but this is also because of its assumption of the physical existence of instants, spatial points and space-time points (and as such, the resulting assumption of the existence of time, space, and space-time). As soon as one recognizes that instants, instantaneous magnitudes, space-time points etc, do not exist, however, motion and change become possible, and can be seen to be completely compatible with gr and the block view, with all times (those shown by a clock) sharing equal footing.

Also, in order for change to be possible, one does not need time to exist, as one only need motion. Indeed, I think that if one thinks carefully about it, it becomes apparent that it is motion that enables the hands of a clock to rotate and for one to represent an interval, rather than the other way around (the existence of time enabling motion). My essay (and notes) go into this further. I naturally agree that certain processes are not time reversible, but this is completely compatible with a timeless block view (if interpreted correctly). Moreover, it does not suggest at all that time flows.

Best wishes

Peter

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Dear Peter Lynds,

Thank you for your response. You state “it can be shown that if instants (and instantaneous magnitudes) existed, motion and change would be impossible. Furthermore, as instants would constitute the building blocks of time, if they can't/don't exist, neither can time.” I presume you are referring to the Zeno’s paradox argument, presented in your own fqxi essay and...

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Dear Peter Lynds,

Thank you for your response. You state “it can be shown that if instants (and instantaneous magnitudes) existed, motion and change would be impossible. Furthermore, as instants would constitute the building blocks of time, if they can't/don't exist, neither can time.” I presume you are referring to the Zeno’s paradox argument, presented in your own fqxi essay and elsewhere. However I do not accept that argument, for the following reason: many discussions of quantum gravity conclude that at the very smallest scale, space-time will be discrete, for this is how the basic quantum theory principle will manifest itself in the context of the nature of space-time (quantized area and volume operators are one of the main deductions from loop quantum gravity, and there are 701,000 web-pages identified by a Google search for “discrete space time”).

I concur in this view both because of quantum principles, and because this rids physics of the profound problem of the uncountable infinities of numbers that occur in the real line of mathematics. Indeed David Hilbert in a famous passage [D Hilbert (1964), ``On the Infinite". In Philosophy of Mathematics, ed. P Benacerraf and H Putnam (Englewood Cliff, N. J.: Prentice Hall), pp 134-151] stated that “Our principal result is that the infinite is nowhere to be found in reality. It neither exists in nature nor provides a legitimate basis for rational thought . . . The role that remains for the infinite to play is solely that of an idea . . . which transcends all experience and which completes the concrete as a totality." On this view, infinities are mathematical entities that never occur in physical reality; this may be taken as applying to the nature of space in a profound way. Incidentally, at a stroke this gets rid of many of the divergences that plague theoretical physics.

If space-time at its foundations is discrete, then the Zeno’s paradox argument falls away. In this case it is not time that is an illusion, it is space-time continuity that is an illusion, generated by the coarse graining that underlies all macroscopic physics and hence also chemistry and biology. Furthermore, you state that most people believe that Zeno’s paradox is resolved by calculus; but this ignores that fact that one of the great advances in mathematics was the transition from calculus to analysis, where the taking of limits is replaced by the use of bounding methods (utilising the famous `epsilons’ and `deltas’ of analysis) and the associated characterisation of solutions in terms of Sobolev spaces. Mathematical physics got rid of those troublesome limiting processes decades ago.

So my position is that continuity is an illusion, and your argument does not apply to the real physical world. Finally you state “in order for change to be possible, one does not need time to exist, as one only needs motion. Indeed, I think that if one thinks carefully about it, it becomes apparent that it is motion that enables the hands of a clock to rotate and for one to represent an interval, rather than the other way around (the existence of time enabling motion).” I cannot understand how you conceptualise motion without the flow of time to underpin it. Motion is identified by something being in a different position at a later time than at an earlier time. Perhaps your view is related to a relative rather than absolute view of the nature of space and time; that is a further interesting argument, which I will not enter here, except to comment that I believe there may be a fundamental duality between absolute and relative views of the nature of space and time. But adopting a relative view of space or time will still leave one with change taking place as relative time flows.

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Dear Professor Ellis,

I enjoyed your essay. You might take a look at mine, which has a similar perspective (it focuses more on suggesting how reduction occurs).

-- Adam Helfer

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Dear George,

Thanks for your thoughtful reply. I appreciate it. In relation to time and space being quantized, and as I mentioned on Carlo Rovelli's essay thread, by assuming that time and space are quantized, and come as minimum, indivisible intervals, one is also assuming the existence of instants in time and spatial points to bound and determine such intervals. If such instants and...

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"Where are they, these instants?"

Where are you?

Tom

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Dear Adam Helfer,

yes indeed, your paper has a very similar perspective to mine. We both agree that determining under what circumstances a measurement takes place is a key element of quantum theory. This is what is missing, for example, from Carlo Rovelli's prescription of `timeless quantum mechanics' (Section 5 of his fqxi essay). His dynamical description does not include any way of determining when unitary development will be replaced by projection, so his formulation of QM is timeless because it is causally incomplete. This is Penrose' key point, developed in The Emperos's New Mind and The Road To Reality, and is what you tackle in an interesting way. I will have to consider it longer to see if I find your approach compelling or not, but certainly your paper tackles a key element of the whole question, which is usually neglected.

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Dear Peter Lynds

thanks for the detailed response. I still have difficulty grasping your position. "A better definition might simply be, motion is defined by something having a changing relative position" - well how can it change without time flowing? I don't get it. You say "an assertion that is physical continuity which is basic and fundamental rather than interval, could equably be reversed ... Yet, they are also mutually exclusive, in that only one can be fundamental and come first". The last statement may not be true - there might be dual viewpoints that are equally valid, depending on one's starting point or perspective (duality relations are all the rage in theoretical physics nowadays). You ask, "Given that you seem to believe that instants in time exist, can I ask why you believe this? Where are they, these instants?" They are everywhere and everywhen, as they are the constituents of space-time; but they are not (as perhaps implied by the name) point-like or infinitesimal, rather they are of finite duration, or equivalently of finite space-time content (a Planck volume, perhaps). Why do I believe this? Because a space-time picture provides a good description of the context within which things happen; but for the reasons I indicated in my previous post, it is reasonable to believe it is quantized at the fundamental level.

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Dear George,

Regarding the so-called dark energy, you wrote (Dec. 10, 2008 @ 21:41 GMT):

"I do indeed have views on that issue, but see no reason to post them here."

Please do not impoverish your readers, and shed some light on all that "dark" stuff, Cold Dark Matter included.

Thank you very much in advance.

As ever yours,

Dimi

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The idea of evolving block universe looks to me as a way to try to unify two notions of time. In topic370 I outline in my paper how time is a scaling principle, where the "block" is the tesselation and the "evolute" is a branching pattern of probable paths a particle may take.

In general relativity the proper time ds = sqrt(g_{ab}dx^adx^b) has a relationship to a clock. The coordinate variable t is a chart dependent calculating device. This coordinate time only approximately has a clock meaning for a spacetime with some asymptotically flat region, such as a black hole sitting in a spacetime that is flat far removed from r = 2GM/c^2. Spacetimes in general do not provide this convenience. Quantum mechanics on the other hand involves dynamical wave equations which explicitly use the coordinate time t. The Schrodinger equation and relativistic wave equations all do this. So the coordinate time is treated as a physical parameter for the dynamics of a quantum wave. As a result some hard work is required to place quantum fields in spacetime (equal time commutators etc), and this leads to some curious physics for quantum fields in curved spacetimes, which in turn leads to the radiation emitted by black holes.

Because of this there exists a dichotomy in our concepts of time between general relativity and quantum mechanics. This is related in part to the problem of quantizing gravity, for you are attempting to quantize a field theory with one concept of time according to a procedure which requires another concept of time.

So time is measured in a sense relative to other “times,” which can be a matter of different time scales. J. Barbour has a fun paper which talks about this. I argue this is physics for a renormalization group for conformal fields. Yet time has always been a relative or comparative matter. Galileo measured the periodicity of a chandelier by using his pulse, presumably as the story goes during a mass. He then later used a clock to measure the periodicity of a pulse. If you have one clock you always know what time it is, but if you have two you might not. With measuring spatial distance we compare one distance according to some established length, a meter stick. So in some ways we do much the same thing. If one is to consider time as strange and maybe not existing the same really has to apply to space.

General relativity is a relationship system between particles that involves geometry. Quantum mechanics is another relationship system which fundamentally relates particles to each other by an abstract Hilbert space of states. Quantum wave equations emerge by our representations of quantum states in spacetime, which have some funny elements to it. The fact that general relativity and quantum mechanics are different relationship systems between particles is manifested in the dichotomy in how the two define time.

Lawrence B. Crowell

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Professor Ellis,

"Finally you state “in order for change to be possible, one does not need time to exist, as one only needs motion. Indeed, I think that if one thinks carefully about it, it becomes apparent that it is motion that enables the hands of a clock to rotate and for one to represent an interval, rather than the other way around (the existence of time enabling motion).” I cannot understand how you conceptualise motion without the flow of time to underpin it."

To add a point to the conversation; Keep in mind that while the observer goes from past events to future ones, these events are first in the future, then in the past. So if time is a fundamental dimension along which reality travels, we proceed from past to future. On the other hand, if time is simply a consequence of motion, then each event being replaced by the next means time is these series of occurrences going from future potential to past circumstance. So the question raised is whether there is a fourth dimension along which we travel from yesterday to tomorrow, or does tomorrow become yesterday because the earth rotates?

Peter,

"This poses a brilliant paradox, as, and although the same cannot be said for a specific interval of time or space due to, by definition, their requiring the existence of instants and spatial points to bound and determine their respective values as intervals, this indistinguishability also makes it impossible, in purely logical sense anyway, to say whether it is physical continuity, and as such, motion and change, which is basic and fundamental (with interval having no physical existence), or if it is the existence of interval which makes continuity possible."

The energy of the motion goes from past events to future ones, i.e, cause and effect. On the other hand, the information defining this energy, the events/intervals themselves, go from future potential to past circumstance. To the hands of the clock, the numbers on the face go counterclockwise.

It's my position that the earth rotating causes tomorrow to become yesterday, so time is not the cause of motion, but a description of it, similar to temperature. While temperature, as a scalar average, might be localized as a reference point, time, as units of motion, cannot be described as a dimensionless point, unless the motion has completely stopped. So from my perspective, Peter is right. Motion causes intervals, as the rotation of the earth causes days. Nor can these intervals be dimensionless.

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Dear George,

Thanks for your response.

"...well how can it change without time flowing? I don't get it."

One can imagine a body moving, while the hands of a clock rotate, with both simply being a function of the capability for motion in Nature. That is, (in my view,) it is simply motion that enables change and the hands of a clock to rotate (and for one to represent an...

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Dear Dimi Chakalov

the Appropriate Content Guidelines for this Forum include

"Posts may not contain language or content that is:

[...] Excessively outside of the scope of the current topic

[...]". The current topic is The Nature of Time. You can see my views on the topic of Dark Energy at http://xxx.lanl.gov/abs/0811.3529.

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Dear Lawrence B. Crowell

thank you again for another interesting elaboration. I agree with what you say. As regards time in General Relativity, one of the best statements on how it works is provided by J L Synge in his book General Relativity. Time in GR is represented as integrals along particle world lines, related to measurement and physics by ideal clocks (which of course being physical opjects move along timelike world lines). The underlying assumption is different such clocks (atomic, electromagnetic, mechanical, etc) will all concur on one universal concept of time (`proper time') along the world line. A key issue here is how quantum based clocks measure time relative to classically based clocks; and of course also clocks are sensitive to gravitational potential energy, as exploited by David Wiltshire ih his fqxi essay. Space is determiened by radar measurements from a world line, and all other physical eneities can be expressed in units of time (see the tabl;e at the back of Synge's book); thus clocks are the foundation of all other physical measurements. How this all relates to quantumn theory (and quantum gravity) ideas of time is then a key issue, as you interestingly point out.

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addendum: sorry about the typos in my last post, but it's menaing is clear enough that I will not repost a corrected version.

The additional comment is that there are `times' that occur in each of the fundamental equations of physics: Newton's equation, Maxwell's equations, the Schroedinger equation, the Dirac equation, general relativity when expressed in the 1+3 covariant formalism. Now these different times along an arbitrary world line could have been incommensurate, but in fact they turn out to be the same (up to a constant that can be normalised to unity by choice of units). That is the deep feature that leads to a consistent concept of time along world lines, mentioned in my last posting. Perhaps this is because all these equations are effective equations deriving from a single deeper unified theory, and it is this common origin that leads to the different times being being consistent.How this could all arise from a unified theory of quantum gravity and fundamental interactions is then what needs clarity.

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Dear John and Peter,

Thanks for the postings. As regards your proposals that we derive time from motion, I think the problem is that we get so used to way time flows that we take it for granted without even realising we are doing so. Thus my challenge to you is, if motion is primary, how do we derive and measure time from it? How do we even identify and measure the motion in the first palce? The thing is that in so doing, you are not permitted to say "first do this and then do that", because that already presupposes the flow of time - but you are supposed to be deriving time from the process. You can't propose any process whatever with a sequence of events to be carried out one after the other, because `after' does not exist as a concept until `time' (and the arrow of time) has been somehow admitted to exist. So the project simply is not coherent, in my view. But maybe I am missing somethng. In any case, that is my problem with your proposals.

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"You can't propose any process whatever with a sequence of events to be carried out one after the other, because `after' does not exist as a concept until `time' (and the arrow of time) has been somehow admitted to exist. So the project simply is not coherent, in my view."

Well put, George. There are perhaps an infinite number of propositions that are philosophically acceptable and internally self consistent, yet empty of scientific content. Motion without time (even if it's only an apparent measure rather than physically real) is one of them.

Tom

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Peter,

Yes, only the "energy" exists. Its "arrangement" is an information state that is constantly changing.

George,

I'm not arguing time doesn't exist, rather that it is a consequence, not the basis, of motion. Temperature is an averaging of motion and doesn't effectively exist if we examine the level of activity where it becomes singular motion, but emerges as an effect of a quantity of motion. Similarly time doesn't effectively exist if we can't derive distinct units and progression of motion. So your point; "You can't propose any process whatever with a sequence of events to be carried out one after the other, because `after' does not exist as a concept until `time' (and the arrow of time) has been somehow admitted to exist." is completely valid. It is just that "sequence" is a consequence of motion, not the basis for it.

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The matter of what is a good clock seems to have no complete answer. This is a good thing really, for it keeps us in business. The smallest clock I could imagine is a quantum gravity clock. This measures the unit of time T_p corresponding to the circumference of a black hole equal to its own deBroglie wavelength, L_p = sqrt{G hbar/c^3}. The Nyquist theorem tells us that you need a system with twice the frequency of the system you are timing to get an accurate measurement. So any time measurement on a scale less than 2T_p is hopeless, and since you are using the quantum system of time to measure units of time, even if multiple units, of that same system we are ultimately in a bootstrap problem.

The Dec 5 AAAS issue of Science has an interesting article by Eckle et al on using quantum tunnelling in ionized helium to measure atto-second 10^{-18}sec time intervals. It is interesting that equation #1 is an parameter determined by the ratio of an ionization potential and the electric field, or maximum pulse field intensity, of the laser pulse. This parameter determines freq*delta time. So here is a measurement of time based upon a relative ratio of physical quantities which one measures to infer a time.

Time is a quantity which will always be determined by the relative scale of two systems or similar systems at different energy. This is the basis of my work to show that time is in cosmology and AdS~CFT determines a renormalization group for the scaling of field theory. Or might it be better to say that this relative scaling determines what we call time.

Cheers,

Lawrence B. Crowell

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PS, I forget to include my take on the matter of atomic clocks vs mechanical or classical clocks. I would say that an atomic clock is good so long as the spacetime curvature is infinitesimal on the scale of the atom or the clock. So if r' - r = 2m ln(|r - 2m|) is tiny the atomic clock should determine a time with some measure of fidelity. This of course become strange when one considers huge curvatures or for very small regions of spacetime where the metric fluctuation &g_{00} = 2&m/r, &m = planck mass, and when r approaches this scale.

Mechanical clocks work great up to the quantum or atomic limit, and you have no funny issues of Heisenberg uncertainty involved.

Lawrence B. Crowell

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George wrote (Dec. 12, 2008 @ 03:59 GMT): "You can see my views on the topic of Dark Energy at http://xxx.lanl.gov/abs/0811.3529."

Thank you. In your arXiv:0811.3529v1 [astro-ph], you wrote:

"Overall: theory must be subject to experimental and/or observational test; this is the central feature of science. There is good progress in this respect as regards both dark matter and dark energy."

I am interested in your solution (if any) to the problem of gravitational energy, from 1918.

If you can suggest 'the right question' and its 'right answer' (cf. MTW, p. 467), I suppose you will have a sound theory to build your speculations about some "quintessence" or "multiverse", say.

I wish you best of luck.

Dimi

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Dear Dimi Chakalov

The Appropriate Content Guidelines for this Forum include "Posts may not contain language or content that is: [...] Excessively outside of the scope of the current topic [...]". The current topic is The Nature of Time.

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Dear Prof George Ellis,

Beautiful and very convincing essay. Indeed, the time is not at the center of attention of modern theoretical physics. Only two theories - special and general relativity are exception, and our point of view to the time is formed basically by these two theories. In an essay The Theory of Time, Space and Gravitation the time is consequence of the motion. This means, that the time in a microcosm differs from the time in a macrocosm similarly to difference of character of motions in these worlds.

Regards,

Robert Sadykov

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George Ellis wrote on Dec. 12, 2008 @ 17:31 GMT:

"The current topic is The Nature of Time."

Exactly. Such as its origin and driving force, as in the case of the cosmological time arrow.

Which brings us to the "dynamic dark energy" and -- inevitably -- to the "non-tangible" (Sir Hermann Bondi) gravitational energy, without which we cannot say anything on its "dark" counterpart, in both DDE and CDM.

But if you've found a way to disentangle time from energy, then I would agree with you.

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Dear George,

Thanks for your comments.

"I think the problem is that we get so used to way time flows that we take it for granted without even realising we are doing so."

Yes, I agree. We feel that time flows, we feel that there is something crucial and fundamental about the present, and we assign events to past and future. However, all of these things are completely subjective. Indeed, in relation to our seemingly innate conception of a present moment or now, I think it extricably tied up with consciousness, hence why it seems so crucial to us.

In relation to meeting your challenge, with all respect, I thought I just did that. Here is the relevant text.

One can imagine a body moving, while the hands of a clock rotate, with both simply being a function of the capability for motion in Nature. That is, (in my view,) it is simply motion that enables change and the hands of a clock to rotate (and for one to represent an interval with a clock), rather than the existence of time enabling motion and the hands of a clock to move.

....This is a faulty definition, as, by talking about later and earlier, it already assumes tense. A better definition might simply be, motion is defined by something having a changing relative position. Moreover, if one simply refers to the continuous readings of a clock, one needn't invoke or refer to tense, past or future etc. That is, one can still assign such readings an order without referring to time.

Best wishes

Peter

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Dear Professor Ellis,

If you did read my essay you would understand why someone tried to hinder me posting further details. Accordingly I could not expect to meet here somebody who fully shares my views.

I gave you a restricted vote because appreciate a lot of sound reasoning in your essay.

Incidentally, some ideas of mine go back to my talks with Jacobus van Wyk who lived in your country. I hope he is still alife.

Sincerely,

Eckard Blumschein

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Peter, I honestly cannot understand that you don't see that your idea of motion without time implies change without energy. You wrote to George Ellis: "In relation to meeting your challenge, with all respect, I thought I just did that. Here is the relevant text.

"One can imagine a body moving, while the hands of a clock rotate, with both simply being a function of the capability for motion in Nature. That is, (in my view,) it is simply motion that enables change and the hands of a clock to rotate (and for one to represent an interval with a clock), rather than the existence of time enabling motion and the hands of a clock to move."

Don't you realize that there is an exchange of energy in the physical motion of the hands of the clock and that that exchange is transitive? One does not just imagine it.

You can certainly hold an essentialist philosophical view that motion is a simple property of nature--but you can't do any physics with it. George said, "Thus my challenge to you is, if motion is primary, how do we derive and measure time from it? How do we even identify and measure the motion in the first palce? The thing is that in so doing, you are not permitted to say "first do this and then do that", because that already presupposes the flow of time - but you are supposed to be deriving time from the process. You can't propose any process whatever with a sequence of events to be carried out one after the other, because `after' does not exist as a concept until `time' (and the arrow of time) has been somehow admitted to exist."

Position and momentum are physical, not philosophical.

Tom

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Tom,

Yes, the transitive process is time, but as the physical reality of the present proceeds from one moment to the next, this series of events goes from future potential to past circumstance. The energy that exists manifests the events, but it is the series which is time and it goes from being in the future to being in the past. Time exists as a consequence of motion, not its cause.

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Dear Tom,

In relation to George's comment, again, one can assign the readings of a clock an order without referring to time and tense, before/after, past/future etc. For example, because 1, 2, 3, is simply a sequence of numbers, one can say that, in their given order, 2 follows 1, and 3 follows 2, without referring to time and tense.

In respect to position and momenta, one can certainly ascribe a moving body momenta, in the same sense as a moving body can be said to be in motion within some time and space interval (as represented by a clock and meter). In relation to accuracy, such intervals could naturally potentially be taken up to the limits of possible measurement. However, by virtue of the fact that for a body to be in motion its relative position has to be constantly changing, it cannot have a determined or instantaneous relative position. The same then applies to instantaneous velocity, momenta and any other instantaneous magnitude.

In relation to your comment about motion without time implying change without energy, I think you aren't quite grasping how, without time, continuity is still possible. If there is simply motion (without time), the hands of a clock can still rotate, so the continuity of all other physical processes, including energy transfer, is naturally possible too. Indeed, such continuity would only not be possible if time (and as such, instants) did exist.

Best wishes

Peter

PS: Unless George prompts it, I think it could be a good idea to round off this discussion.

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Peter,

You wrote, "In relation to George's comment, again, one can assign the readings of a clock an order without referring to time and tense, before/after, past/future etc. For example, because 1, 2, 3, is simply a sequence of numbers, one can say that, in their given order, 2 follows 1, and 3 follows 2, without referring to time and tense."

No, one cannot. The order is not the issue--transitivity (along with identity and refexivity) is a fundamental property of an equation. When you sacrifice all mathematical language to describe the physics, you sacrifice numbers, and you can't do physics at all. The claims in your second paragraph are therefore obviated.

You wrote: "In relation to your comment about motion without time implying change without energy, I think you aren't quite grasping how, without time, continuity is still possible. If there is simply motion (without time), the hands of a clock can still rotate, so the continuity of all other physical processes, including energy transfer, is naturally possible too. Indeed, such continuity would only not be possible if time (and as such, instants) did exist."

If you know your Einstein, you know the limits of continuous function physics. Discontinuity is not only possible--it's demonstrable. Einstein was part of that revolution, too.

"PS: Unless George prompts it, I think it could be a good idea to round off this discussion. "

George did prompt it. He wrote an essay supporting the flow of time in physics, and my comments are on topic. The arguments are all on the table, however, so any more comment would be redundant.

John,

It's irrelevant to the flow of time whether time is a simple parameter of reversible direction, as in a relativistic description, or a measure of motion as in classical mechanics, e.g., Mach. Any physical description of an event is transitive.

Tom

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Peter,

Most motion is effectively at the speed of light. As a consequence, our brains must process it as sequential impressions of extremely limited information, like frames of film, otherwise it would overwhelm our senses. So it is necessary and logical that we perceive motion as a series of instants.

The traditional view of time is this series laid out from beginning to end and any position on it as subjective. While time is this series, what animates it is the energy illuminating one frame/event at a time. So as the film is played, it goes from being in the future to being in the past. Even our own lives are units of time which start in the future and reel off into the past. Cosmology views the entire universe as a unit of time that goes from beginning to end, yet it starts in the future and ends up in the past. The only way this relationship holds is if time is the series of events being created and consumed by motion.

Pardon me, George.

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Tom,

Any measurable relationship is necessarily discontinuous. Otherwise there is no relationship to measure.

Question; Does time go from past to future, or from future to past?

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Dear Dimi Chakalov

I do not believe that either dark energy or dark matter have anything more particular to do with time than any other form of energy or matter, which are of course implicit in my view, in that it is through them that time becomes manifest (specifically: clocks are made of matter and function through energy use).

If you want a more specific take on the possible relation of matter/energy to the emergence of time, please see the interesting essay in this forum by Adam Helfer, to be found at at http://www.fqxi.org/community/forum/topic/380.

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Dear Tom, Peter and John:

The views you express in this interesting interchange are obviously deeply held. My own opinion is however unchanged after reading it. But I have the following questions that arise.

Firstly, is there any way you can see to experimentally *prove* that "time exists as a consequence of motion, not [being] its cause"? What actual laboratory demonstratin would show this to be true? If there is none, maybe this is a philosophical rather than physics discussion between two dual but equally allowable philosophical stances that "explain" the same physical phenomena.

Secondly, and essentially following from this line of thought, suppose I were to accept the proposition "time exists as a consequence of motion, not its cause". What difference would it make to the theses I propose in my essay? Would it not perhaps even then be true that the time that emerges in this way in fact flows as I discuss in my essay, and is best conceptually represented by an Evolving Block Universe rather than a static unchanging space time?

The deep underlying philosophical issue is whether the blcok universe (evolving or not) just REPRESENTS in the best possible way the way time/spacetime is (the epistemological view), or IS the way time/spacetime is (the ontological view). I am agnostic on this issue, supporting the Evolving Block Universe in either case.

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Dear Dr.-Ing. Blumschein

I have already given you my comment on complex numbers. However I see you also comment in your paper on problems to do with negative numbers. The relation to my view is that proper time along any specific world line is defned up to an affine transformation: t -> t' = a t + b, where a and b are constants. This can be used to set any specific chosen event on that world line to be the event "t=0". Cosmolgists like to set this to the start of the universe, when (on the usual view) time actually began. But for local use it can be used to specify any other particular event, as when one starts a stop watch when a gun is fired at the begining of a race. All events prior to that one are then assigned negative times, but there is no physical implication: it is just a useful cooordinate convention [this is of course what happens in the Christian calendar, when times AD are assigned positive values and times BC are essentially assigned negative values].

Finally your paper, and one or two comments by others, raise the issue of whether time is continuous or not. As I believe space-time itself is quantised, it should follow that proper time along any world line too is quantised. But through coarse-graining, this will make no difference on any scales above the Planck scale: for all practoial purposes ("FAPP"), time will seem to be continuous (this is associated with the fact that the human mind can only discern time differences down to a finite limit, based in the way neurons operate]. But this quantised nature will rid us of all the problems associated with the uncountable infinity of numbers that occur on the mathematical real line [I commented on this in a previous posting].

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The readers of this thread may or may not be reading also Carlo Rovelli's very active thread. For those who are not following that thread, I would like to post here a comment I made there in response to a post by Vesselin Petkov, as it represnts a possible significant shift in my own position. It reads as follows:

You state "It becomes evident that the growing block universe model also contradicts relativity - the hypersurface (no matter how complex its shape might be) on which the birthing of events happens constitutes an objectively privileged hypersurface (existence is absolute!) and therefore an objectively privileged reference frame." I tried to argue that one should think only in terms of evolution at space time events or along world lines, and not try to consider the relation of times along different world lines and so on spacelike surfaces. However if one insists on doing so and considers relevant spacelike hypersurfaces, then yes, an objectively privileged time frame exists. There is nothing new in this: every physically realistic solution of Einstein's equations has preferred space sections, being just another case of the broken symmetries that are so fundamental in present day theoretical physics (the underlying equations have higher symmetries than their solutions). The classic case is the Friedmann-Lemaitre cosmological solutions of general relativity: no one in their right minds uses any time coordinate other than the preferred time coordinate that is always used! (which is of course proper time measured along the fundamental world lines). Objectively privileged hypersurfaces do indeed exist in standard cosmology, and in all physically realistic solutions. And in the end, the real-world evidence that time does indeed flow is overwhelming (example: this posting was not posted till I posted it at a particular proper time along my world line); if this demands that preferred space sections exist, so be it, too bad for any theory that denies their existence in the face of this evidence. The quote from Omar Khayam in my essay refers.

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Dear George,

"Firstly, is there any way you can see to experimentally *prove* that "time exists as a consequence of motion, not [being] its cause"?"

My position is that time doesn't exist in any physical sense. That I think this should be clear. Fair is fair George.

As for a test, we already know that motion is possible, but no manner of test is ever going to confirm the existence of time. It is just never going to show up.

"If there is none, maybe this is a philosophical rather than physics discussion between two dual but equally allowable philosophical stances that "explain" the same physical phenomena."

No, because one is a physically based interpretation (motion, change), while the other (time existing) can have no physical basis. The latter can also be shown to cause all manner of paradox and the opposite of what it is supposed to achieve. In relation to your essay, given that I am talking (as is Carlo) about time not actually existing, this would mean that it is fundamentally wrong. Moreover, in relation to space-time, and as I've already pointed out, if time (and instants) are assumed to exist, one can forget about any evolution.

Finally, on Carlo's essay thread you said:

"And in the end, the real-world evidence that time does indeed flow is overwhelming (example: this posting was not posted till I posted it at a particular proper time along my world line); if this demands that preferred space sections exist, so be it, too bad for any theory that denies their existence in the face of this evidence."

Again, you seem to be either not grasping or ignoring what I just explained to you. As you know, proper time refers to a local clock. This clock represents the crux of the matter. The rotation of the hands of a clock can be seen to simply be a function of the capability for motion in Nature, and does not require time to flow/exist. Moreover, a clock does not actually measure time. As it only refers to itself, it itself "represents" time. As I've mentioned elsewhere, I think it is interesting to note that the quote "time what a clock measures" is usually attributed to Einstein. That Einstein would have said this puzzled me, particularly as a key feature of the dilation of time in relativity was Einstein's treatment of time as being nothing more than that what a clock showed. On locating Einstein's original quote, it came as no surprise to find that what he actually said, "Zeit ist das, was man an der Uhr abliest," translates to "Time is what one reads off the clock." Although the difference seems tiny, as "measure" says that time exists, while "reads" neither affirms or denies its existence (but leans towards the latter), the difference is actually quite big.

Best wishes

Peter

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George, you wrote, "The deep underlying philosophical issue is whether the blcok universe (evolving or not) just REPRESENTS in the best possible way the way time/spacetime is (the epistemological view), or IS the way time/spacetime is (the ontological view). I am agnostic on this issue, supporting the Evolving Block Universe in either case."

I would hope that you see from my previous comments that I agree without qualification. Evolution is definitively a time dependent phenomenon. Further, if one accepts Brouwer's intuitionistic philosophy of mathematics, the language independent of meaning already presumes a "...move in time." Even an epistemologyical view, then, demands a time-dependent representation.

Tom

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George, Peter, Tom,

The principle by which time consists of discrete units is not exclusive to the microcosmic. Think in terms of geologic earthquakes, political upheaval, or economic collapse. While the surface description is basically static, underlaying tensions are building that are not linear and thus the sudden change isn't completely predictable. Ref. Complexity Theory. So to, two points in time may not be connected in a linear fashion, but could have a hologram of the entire universe between them, but they are still connected, otherwise they would be outside each others light cone and effectively not exist to one another.

The reason block time and multi-worlds are necessary is to explain probability in forward moving time. The future is defined by probabilities and if time is a linear dimension from past to future, the need is to explain how the issue of chance is resolved. Block time is essentially determinism, where the probabilities are an illusion and ultimately time is laid out in a linear dimension. Multi worlds takes the opposing view and argues all possibilities branch out into separate realities. There are varieties of combinations of these two extremes, as evolving block time would be.

The advantage of time as an emergent description/consequence of motion is that since this series of events is being both created and erased by this jumpy/continuous motion, time is the series of events going from being in the future to being in the past. So the issue of probabilities is resolved by the collapse of potential into the actual. It is also efficient in that the same energy manifests all points in time and doesn't require additional dimensions of energy to manifest each and every moment.

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George,

You wrote (Dec. 15, 2008 @ 09:10 GMT): "I do not believe that either dark energy or dark matter have anything more particular to do with time than any other form of energy or matter, ... "

I'm afraid you're changing the subject. Here's what I wrote (Dec. 12, 2008 @ 19:56 GMT):

"Which brings us to the "dynamic dark energy" and -- inevitably -- to the "non-tangible" (Sir Hermann Bondi) gravitational energy, without which we cannot say anything on its "dark" counterpart, in both DDE and CDM."

To make your task easier, please put aside the driving force of the cosmological time (DDE), and focus on its mundane counterpart -- the "non-tangible" gravitational energy. The task is on the table since 1918.

Have you found a way to disentangle time from energy?

You also wrote (Dec. 15, 2008 @ 09:10 GMT): "If you want a more specific take on the possible relation of matter/energy to the emergence of time, please see the interesting essay in this forum by Adam Helfer, to be found at at http://www.fqxi.org/community/forum/topic/380."

Please read there my posting to Adam Helfer from Dec. 11, 2008 @ 20:14 GMT.

Dimi

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Dear Dimi Chakalov

I am not going to enter this discussion with you. The person who is continually trying to change the topic is yourself. The Appropriate Content Guidelines for this Forum include "Posts may not contain language or content that is: [...] Excessively outside of the scope of the current topic [...]". The current topic is The Nature of Time. I am not interested in a debate on the nature of gravitational energy. Please save us both a lot of bother by desisting this series of postings.

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In physics there are three types of entities, kinematic, geometrical and dynamical. A perfect example is with Newton's second law of motion F = ma which is

dynamics = kinematics times geometrical

The stuff we measure or observe in physics are kinematical and dynamical. Dynamical entities are the primary thing of interest of course. Kinematical ones are a tad strange, for in weighing a mass you put it on a scale to compare its F = mg against the F' = Mg across a moment arm. Then there are the geometrical ones, which have to be measured relative to some physical objects, say a measuring stick or by comparing the periodicities of dynamical systems, one being defined as a clock.

Whether or not tiime exists amounts to asking whether or not geometrical entities exist. If one is to be concerned about the existence of time it might be best to extend this to space as well. Do they exist? To be honest I don't think that science can answer such existential questions. They are useful constructions, and just as with F = ma they help us understand something about the things physics actually measures directly.

Lawrence B. Crowell

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P.S. to my previous post;

As the interludes between the transitions are non-linear activity, they are best described in scalar/averaging terms, such as temperature, pressure, etc.

As opposed to time being a vector.

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On Dec. 15, 2008 @ 15:22 GMT, George Ellis wrote:

"The current topic is The Nature of Time. I am not interested in a debate on the nature of gravitational energy."

Fine.

Can you solve the Cauchy problem for Einstein field equations with your 'preferred time variable in GR' or with 'the meaningful physical time $tau$ along world lines'?

Can you add something to your notion of finite infinity, from 1984 (ref. [54] in your arXiv:gr-qc/0102017v1)?

What is the intended application of your ideas?

For if they are fruitful, their inevitable and immediate application will be for sorting out the puzzle with the nature of gravitational energy, which is known since 1918.

This is, in my opinion, your 'proof of the pudding'.

I've been studying your articles, manuscripts, and monographs since 1972, and can assure you that you've always stated your objectives clearly. Not with your current essay though.

I will be happy if you do it before January 1, 2009. As I showed previously in this thread, the approach taken by Carlo Rovelli is logically inconsistent. I trust you can do better.

Dimi Chakalov

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P.S. I should have written: "As I showed previously in this thread, the approach taken by Carlo Rovelli is logically inconsistent." Please notice the link; sorry for not doing it in my preceding note. My postings to Carlo Rovelli's thread are from Dec. 12, 2008 @ 16:21 GMT, Dec. 13, 2008 @ 13:01 GMT, and Dec. 14, 2008 @ 14:01 GMT.

D.C.

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George,

Thank you.

I had never heard of the “block universe” before I entered this contest and I find its applications to quantum physics probabilistic nature fundamentally flawed. The block universe MUST be probabilistic and evolve. Thank you for beating this into the heads of the quantum curmudgeons. Unfortunately I was not able to comment earlier I just noticed your essay, but I hope that you will still reply. I no longer feel that I am the only person who is championing the fundamental nature of time, the importance of collapse and its relationship to entropy. I also agree that imaginary numbers are mathematical shortcuts because all observables are real. This is why quantum uses Hermitian matrices because their eigenvalues are always real. Understanding the fundamental nature of time requires “real” mathematics. In regards to the evolving block universe do you picture the number of possible world lines to be finite? I also think that if we were to consider all the microscopic variations possible we would discover that the vast majority of them correspond to a small number of macroscopic possibilities. Again this is the entropy argument. I do not want to self promote on your forum, but I entered this contest hoping to get some feedback from an expert eye like yourself. For the evolution of the wavefunction I used derangements (they are real) and a few other combinatorial ideas for entropy and collapse. I would be very interested in your thoughts and feedback.

THANK YOU,

Brian Beverly

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Dear Brian Beverly

Thank you for your comments; yes it seems we basically agree on the issues involved. You ask, "In regards to the evolving block universe do you picture the number of possible world lines to be finite?" Yes I do; as indicated in a posting above, following David Hilbert, I think that "infinity" (i.e. a quantity that can never be attained or measured) is a mathematical concept that cannot occur in the real physical universe. This leads to the view that the universe msy have closed spatial sections, and hence contain a finite number of particles and galaxies, as advocated particularly by John Wheeler. This finiteness has to be the case if the space sections of the universe are positively curved, and is a possibility if they are flat or negatively curved.

You then state "I also think that if we were to consider all the microscopic variations possible we would discover that the vast majority of them correspond to a small number of macroscopic possibilities. Again this is the entropy argument." Yes indeed, please see the very nice discussion of this in "The Emperor's New Mind" by Roger Penrose. Entropy is a measure of the number of microstates that correspond to a given macrostate, and the flow of time is from less probable macrostates (corresponding to fewer microststes) to more probable macrostates (corresponding to many more microstates).

While time can be expected to be correlated with the growth of entropy (this is just the second law of thermodynamics), it is not necessarily linearly related to entropy. Your idea of derangement is interesting, but it is not clear to me that it is a direct measure of time. Indeed I believe that time can flow even if a single body has no interactions with any other body, or a group of bodies move around without interacting with each other. But you maybe still be able to use your basic argument in terms of the volumes of phase space occupied by the objects as they move, even if they don't interact with each other. In a sense they are interacting with the phase space.

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Dear George Ellis,

From the examples you gave on Carlo Rovelli's thread I think by "Objectively privileged hypersurfaces do indeed exist in standard cosmology, and in all physically realistic solutions" you mean "objectively privileged" in terms of description. But that is just a specific foliation of spacetime that does not exist in reality - it is just a result of our *description* of spacetime in terms of space and time. If one assumed that that privileged hypersurface would be really objectively privileged (not just a description) then this would locally lead to a direct contradiction with special relativistic effects, e.g. length contraction as briefly explained on Carlo Rovelli's thread.

Vesselin Petkov

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I have responded in depth to Vesselin Petkov's challenge on Carlo Robvelli's thread , because that is where his detailed argument is posted. There is no contradiction with special relativity effects, basically because the surfaces of coming-into-being do not have to coincide with any specific observer's determination of surfacves of simultaneity in spacetime.

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George,

I stated above (Dec. 15, 2008 @ 18:44 GMT) that the objectives of your essay are not clear, and expressed my hope that you can do better than Carlo Rovelli.

Let me try to explain, by quoting from your postings and inserting my comments.

1. George Ellis (Dec. 11, 2008 @ 12:05 GMT):

"On this view, infinities are mathematical entities that never occur in physical...

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Dear Professor Ellis,

Shift of the origin t'=at+b is possible if we consider time an abstracted quantity. Elapsed time cannot be shifted if it relates to reality. For instance, nobody manages to get younger.

Therefore, I consider elapsed time the original physical quantity, and I am not surprised that it has a natural zero. If we try to pinpoint the nature of time, the distinction between elapsed and abstracted time is a must. I go on claiming that elapsed time is the natural and therefore measurable time.

Accordingly, I do not like to take the world-line for absolutely given. If the universe is the only closed system in the sense of being unique (without anti-worlds) and infinite, then Arnold Sommerfeld's radiation condition tells us that infinity does not reflect anything, and there is no fatum.

While any process still invites to be seen as bundling and freezing many definitely causal influences, the majority of physicists looks into the opposite and uncertain direction of unseen future ramification.

I also object to any attempt to link the question of continuity or not with perception and limitations to neurons. There is ample evidence for the moon to exists even if nobody looks at it.

My point of view concerning this issue results from what I learned at TU Dresden and then taught at Otto von Guericke university for more than 40 years. A continuous function of time corresponds to a discrete function of frequency and vice versa. Both continuity and countability are mutually excluding mathematical ideals. I will further explain this in connection with Fourier transform and cosine transform

at http://home.arcor.de/eckard.blumschein/M286.html because my posts here were repeatedly mutilated.

Regards,

Eckard Blumschein

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George,

"I think that "infinity" (i.e. a quantity that can never be attained or measured) is a mathematical concept that cannot occur in the real physical universe."

If I may paraphrase this, it would seem to say that because infinity doesn't have measurable boundaries, i.e, is not finite, it doesn't exist?

If I may extend this logic a little further, it could be argued that nothing has finite boundaries, as everything, you, me, the moon, are nodes in some larger network. Even defining the entire universe runs up against dark energy and matter, the possibility of other universes, worlds, dimensions, etc. What came before the Big Bang, where the energy of the universe goes next etc. It would seem quite difficult to argue the entire universe, if it is defined as singular, isn't also some node in a larger network.

So it would seem that no thing has absolutely finite boundaries. Does that mean that nothing is "real"?

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Dear George,

I don't mean this to be offensive or inflammatory, but I realise that it potentially could be. I do keep thinking it within the context of this essay contest (including in relation to our discussion), however, and I think it is a pertinent point. Considering that all argument, reason, and empirical evidence points towards their not existing (and indeed, both are non-material), I see a belief in the existence of time as being almost perfectly analogous to a belief in God; believing in both simply becomes a matter of faith. To follow the analogy a bit further, as is the case with God, there are people who believe that time exists, those who sit on the fence on the issue because they are not sure or haven't given it much thought (the majority), and then there are the time atheists. This cross secton no doubt represents all of the entrants in this contest.

Empirical evidence and observables, reason, physical intuition and insight, all have an important part to play in physics. Faith doesn't. This brings me to another point. Intellectual honesty is obviously very important in science. When there are differing views, it is very important that both sides do their very best to properly consider the opposing position. If that position adds up, and contradicts one's own, one must acknowledge this and not hide one's head in the sand and continue on as though it doesn't. If something is a matter of faith for someone, however, this becomes impossible, as no amount of reasoned argument or evidence is going to change one's mind.

Best wishes

Peter

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Dear George Ellis,

I see you have a lot of posts to address; so do not worry about mine - when you have time.

Thank you for the helpful and constructive discussion. I have been trying to examine the Evolving Block Universe (EBU) view as thoroughly as possible since it is the only serious alternative to the usual Block Universe (BU) view. And I believe we are all interested in...

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George Ellis, Your book with Hawking has been an inspiration to me for 30 years so I am delighted to see your contribution here. It is also wonderful to see that you have made the time to contribute to the discussions here because i think learning from them is more important than winning the contest. I hope you have some time and energy left to answer a few more questions.

My view on time is very dfferent from yours in that I belong to the camp that says time is not fundamental and must emerge from a deeper theory. I think this because of observations based on our attempts to quantise gravity including especially aspects of topology change and finite information limits is string theory. The details are of course in my essay fo anyone interested

http://fqxi.org/community/forum/topic/277

I am not concerned about the lack of absoluteness of time in general relativity of the implicatons of the WDW equation in canonical QG. I would not make statements like "time does not exist" or "the flow of time is an illusion" because I find it hard to attach meaning to these statements. I prefer "time is not fundamental" or "time is emergent from a deeper theory". I think this puts me in a different amp from Julian Barbour for example.

If I have understood corrctly, your claim is that irreversibility is due to wave function collapse in quantum theory. The past and prseent exist but the future does not (yet). I can think of two counterarguments and would be interested to hear your defense.

(1) Irreversibility can already be understood in classical mechanics as argued by Boltzmann. If you start from a low entropy state a system evolves classically to a higher entropy. This suggests that times arrow is due to a low entropy beginning rather than the irreversibility of quantum measurement.

(2) Quntum theory does not provide any record of when wave function collapse has occurred. The wave function can be evolved backwards and it is only our memory and other records that provides any certainty of the past. So according to quantum theory much of our past must be as uncertain as our future.

Indeed I would argue that it is the low entropy of the past that gives the illusion of the irreversibility of the measurement process rather than the reverse.

all the best

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Dear Peter Lynds

Your are entitled to the opinion expressed in your first paragraph, which is indeed your personal belief. Other members of this discussion may have the opposite opinion; that belief in the non-existence of time has the nature you characterise. However the presuppositon and hope of this whole discussion is that one can move beyond simple belief to a rationally supported and scientifically based view.

As regards your second paragraph, you state "Empirical evidence and observables, reason, iphysical intuition and insight, all have an important part to play in physics. Faith doesn't.' Actually a lot of present day theoretical physics is faith based and not supported by empircal evidence and observables. However that discussion is ocmpletely off topic, and I will not pursue it here.

You further state "Intellectual honesty is obviously very important in science. When there are differing views, it is very important that both sides do their very best to properly consider the opposing position. If that position adds up, and contradicts one's own, one must acknowledge this and not hide one's head in the sand and continue on as though it doesn't. If something is a matter of faith for someone, however, this becomes impossible, as no amount of reasoned argument or evidence is going to change one's mind."

I agree. It applies to everyone involved in this discussion.

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Dear Vesselin Petkov

I thank you for your interesting further contribution. The points you raise are on target and significant. Yes please send me a copy of your Montreal talk. I will now try to address your points.

1. Regarding the Weyl quote you gave in your post and your essay: we both agree on the first part of what you say: “if it is EBU the flow of time is objective, not...

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Dear Vesselin Petkov

I thank you for your interesting further contribution. The points you raise are on target and significant. Yes please send me a copy of your Montreal talk. I will now try to address your points.

1. Regarding the Weyl quote you gave in your post and your essay: we both agree on the first part of what you say: “if it is EBU the flow of time is objective, not mind-dependent, and there is no need for what Weyl proposed … if the world turns out to be BU, Weyl's idea appears to be the only reconciliation of the BU and the fact that we realize ourselves at the moment 'now'.” Good. You continue “The brain processes are governed by the laws of physics (although not all agree), but neuroscience does not offer a certain answer to the question whether those processes constitute what we call consciousness (or what Weyl had in mind).” Certainly neuroscience does not understand consciousness, but it is a central belief of the field that brain processes, and hence the functioning of the mind, are indeed governed by the laws of physics, because these underlie the relevant genetic, molecular biology, and neuronal processes. You will be considered unscientific if you propose otherwise (you will be proposing some form of dualism or vitalism). I suggest any serious discussion of the issue nowadays must talk the present day neuroscience consensus into account.

So let me try to make the point in a strong form: if the BU picture is true, there is no special significance to the present instant, both as regards spacetime itself and as regards physical processes in spacetime. Consequently if brain processes and the functioning of the mind are indeed governed by the laws of physics, which I will assume, the BU picture implies there can be no special significance to the present instant as regards brain processes and the functioning of the mind. The mind will therefore be functionally unable to assign any particular significance to the present. I believe this is a complete refutation of the Weyl proposal.

2. You state “I think (i) whether or not something is reversible and (ii) whether or not we can predict something, have nothing to do with the alternative EBU - BU. It is not unthinkable to imagine a BU that is asymmetric and acausal (at least at the micro scale) since existence of objects in such a world is not determined by causality (I think existence is more fundamental than causality).” I acknowledge this is circumstantial rather than direct support of my view, although I myself find it quite compelling. I think it does contradict the BU proposals of some other essays, for example Rovelli’s.

3. Your state “I proposed a thought experiment that involves an *instantaneous* measurement of length contraction and no radar procedure is used.” This is an interesting proposal, but does not contradict the EBU view because while the measurement itself takes place at a single instant, as you yourself acknowledge “we can observe the results only after all pictures of A's meter stick came into existence.” All relevant physical processes take place in the part of the EBU that has already come into being. So the arguments given for a Block Universe in your interesting essay are not undermined: but they only apply to the past of the observational event, and so only imply existence of a BU to the past of that event. The EBU proposal survives that test.

The rest of your points have to do with quantum issues, and I will try to answer them in a separate posting.

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Philip,

Possibly you are open to the idea that time is simply the emergent series of events which go from future potential to past circumstance, as opposed to formulating complex theories to prove the intuition that time is a narrative dimension proceeding from the past into the future.

Several points; Time may be irreversible if entropy isn't a factor, but if these events are dependent on the same quantity of energy, they can't co-exist.

Two; The past is, in many ways uncertain, since it no longer exists and any record or memory is fundamentally affected by the process of recording it, much the same way as the Uncertainty Principle applies to measuring energy.

Three; Since linearity is a function of perception, most activity is effectively non-linear, so the concept of temperature, the scalar averaging of motion, is actually primary to time, which is linear progression of motion. It is simply our singular mobility which makes time primary to our perspective.

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Dear Vesselin Petkov

Continuing my response to your post,

3. You state an argument for the evolving block universe “being as predetermined as the block universe”, based on EPR-type experiments: “when the polarization of a photon is measured, the measurement of the other photon (spacelike separated) might not yet have come into existence, but the outcome is certain (predetermined).” That may be so for this type of experiment, but it is not true for others. The existence of ANY outcomes that are not predetermined suffices to make my case. And they do exist (decay of an excited nucleus, for example).

4. The interesting proposals in Sec. 5 of your essay as regards the double-slit experiment apply equally in a BU or an EBU.

5. You state “As "the surfaces of coming-into-being" are *objectively* privileged (the edge of EBU) only *one* such surface is possible; more surfaces imply relativization of existence (to avoid any misunderstanding - by a surface I mean a spacelike cross-section of the "whole" universe, of everything that exists).” I agree. As I stated, my view now (stimulated by the discussion with you) is that the EBU does indeed involve such a surface of coming-into-being that is absolutely privileged and breaks Lorentz invariance; and this is Ok, as it is just another case of a broken symmetry. The solution to the equations has less symmetry than the equations. That happens all the time in physics.

6: Finally, you state “I wonder, on the EBU view, what was an electron before it hit the screen in the double-slit experiment? The past is there; so the electron should be something in the already realized spacetime block.” I have no particular view on this: whatever can work in the BU case will work in the EBU case also.

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Dear Philp Gibbs

Thank you for the post. I cannot download your essay, as there is some problem with the .pdf file in relation to my computer system.

Your state “My view on time is very dfferent from yours in that I belong to the camp that says time is not fundamental and must emerge from a deeper theory. .. I prefer "time is not fundamental" or "time is emergent from a deeper theory".” I do not think that necessarily contradicts my position: in whatever way time comes into existence, it can possibly have a nature that supports an EBU. Indeed I propose that whatever quantum gravity theory eventually emerges should have such a nature.

You continue “ (1) Irreversibility can already be understood in classical mechanics as argued by Boltzmann. If you start from a low entropy state a system evolves classically to a higher entropy. This suggests that times arrow is due to a low entropy beginning rather than the irreversibility of quantum measurement.”

That is certainly part of the picture. I agree (with Penrose and others) that the cosmological arrow of time is due to low entropy in the early universe. Firstly, that does not contradict an EBU proposal. Secondly, a puzzle emerges out of this: why does the arrow of time of quantum theory (related to collapse of the wave function, see for example The Emperor’s New Mind) coincide with the cosmological one (determined by large scale statistical considerations of a classical kind)? I have no answer but it is an important question.

Finally you state “(2) Quantum theory does not provide any record of when wave function collapse has occurred. … So according to quantum theory much of our past must be as uncertain as our future.” I agree, indeed it is MORE uncertain, as I state in my essay. Quantum theory provides probability predictions to the future but not the past.

You then say ”Indeed I would argue that it is the low entropy of the past that gives the illusion of the irreversibility of the measurement process rather than the reverse.” I cannot see that you have offered a causal connection between the two, nor any reason to call the irreversibility of the measurement process an illusion.

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Thanks for your answers.

I also had problems downloading my essay via the browser at first.

I found two solutions. The first is to right click on the link and use "save as" to download the PDF (the exact procedure may vary with browser and OS of course). You can then view it in acrobat as usual. I later found that if I upgrade acrobat to latest version 9.0 there is no problem with reading it via the web browser. (This upgrade is also recommendeed because of serious security flaws in some versions of acrobat 7 and 6)

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Dear George,

Thanks. Given that, whether one believes in them or not, the past, preset, future, instants etc, are non-material, there can be no "rationally supported and scientifically based" foundation for them in physics. In relation to your comment about a lot of modern physics being faith based, I agree. Indeed, the whole of science is based on faith; faith in objective reality. However, I was clearly talking about faith in the physical existence of things that are non-material, i.e. do not actually have any physical existence!

Best wishes

Peter

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PS: "So let me try to make the point in a strong form: if the BU picture is true, there is no special significance to the present instant, both as regards spacetime itself and as regards physical processes in spacetime. Consequently if brain processes and the functioning of the mind are indeed governed by the laws of physics, which I will assume, the BU picture implies there can be no special significance to the present instant as regards brain processes and the functioning of the mind. The mind will therefore be functionally unable to assign any particular significance to the present. I believe this is a complete refutation of the Weyl proposal."

Your conclusion does not follow, because, while brain processes are governed by the laws of physics, there is no reason why such processes cannot create the experience of a present moment. Indeed, I think the brain does do this, and as I've already alluded to, I think this holds the key to understanding how conscious awareness in possible.

Notwithstanding the above, considering that the BU picture, as normally interpreted, is incompatible with continuity and change, one could forget about the function of any brain processes. As I've already pointed out, however, as long as one recognizes that instants, instantaneous magnitudes, space-time points etc, do not exist, motion and change are compatible with the block view. In respect to assuming the existence of instants etc, and not being able to evolve because if it, the same naturally applies to the EBU.

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Dear George Ellis,

Every author in this contest reflects his bias based on the nature of personality and the quality of mind. Thoughts are intuitive, analytical and inspirational. Mind is run by such thoughts. Individually we all have diferent strengths. One who works in accordance with one's strength becomes successful, otherwise one remains wayward.

Your essay i read so late but i enjoyed its logical presentation. The idea of a Block Universe does simplify the picture of evolution as Time than becomes a mere intrinsic characteristic, just like motion. Nothing in the Universe is seen to be not in some or the other kind of motion. Without any vibration, existence will not appear or take a physical shape. Thus, there appears an interesting aspect of ' consciousness ' a non-physical entity.It may well be a precursor in the creation of the Universe through the Big Bang. Vibrational consciousness becomes the physical reality and gets associated with mass/energy and fields that may well get generated through imperfections/distortions in space/ time, especially in the creative stages.. Without it remains as a sort of immense potential field with no physical exhibition! Thus, the concept of free will, initial and causational aspects can be tackled via the logical pattern of this pure/vibration free consciousness or may i dare say the Unified Field. It may well have some kind of super-intelligence or super mind. Interestingly, it decided to create in Its own image the humans, only after 13 billion years of the existence of the Universe!

Leaving aside this philosophy, may i present to you the multi-universes concept in cosmology and the consideration of multi-dimensionality aspect in relation to the 3-space and 1-time dimension. As it appears well-nigh impossible even to make reasonable cosmological measurements in our universe beyond the 13 billion years in order to examine early universe, the multi-universes appear as a far cry! It seems that science is better restricted to relative truths, better & better in degree, instead of approaching the absolute reality. I agree that it is best to persue science through some precepts and concepts based on critical analysis of available observed facts and then use mathematical tools to develop a theory so-based. Without this Maths should not have a relevance in Physics, as some theoretician like to proceed abstractly.In your post responses you have rightly emphasized Maths as just a tool. Einstein followed the same approach in whatever he did.

May i request if you care to see my essay by a 'pure' experimentalist, providing some innovative prospects in understanding the 'Mysteries of the Universe'. Without the wisedom of theorists i feel like a lame duck in this essay competition with preponderance of theoretical physicists!More can only follow your resonse!

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Dear George,

On Dec. 17, 2008 @ 12:54 GMT, you wrote:

"... why does the arrow of time of quantum theory (related to collapse of the wave function, see for example The Emperor’s New Mind) coincide with the cosmological one (determined by large scale statistical considerations of a classical kind)? I have no answer but it is an important question."

Perhaps because there is no such thing as "arrow of time of quantum theory" in the first place: please check out an essay 'Quantum Mechanics 101'. The link was also provided in the first posting to your thread, from Dec. 2, 2008 @ 07:02 GMT.

I am respectfully awaiting for your professional reply.

Regarding your EBU hypothesis, please also read my specific critical comments from Dec. 16, 2008 @ 14:43 GMT above.

Looking forward to hearing from you,

Dimi

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Dear Professor Ellis,

Instead to post at my M286, I decided to attach the first part of a more reply "How do negative and imaginary numbers relate to reality?"

I tend to blame improper dealing with this matter for some weirdness in modern physics.

What about the question if time is continuous or discrete, you will find the basics for my answer also in the attachment.

What still puzzles me is what one could call the divine or Adam and Eve model of putative causality: God switched on the light. All people are descendants of Adam and Eve. Isn't it common sloppy thinking to call a signal causal if it exists only for future time t larger than zero. In my understanding, all quantities of reality are only measurable within the past even if future can exactly be predicted.

I suspect, it was Ludwig Boltzmann whose thermodynamic probabilistic view mislead Einstein, Markov and all the others.

Regards,

Eckard Blumschein

attachments: 4_Microsoft_Word__How_do_negative_and_imaginary.pdf

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George, I'm going to use your meme for infinity whenever dealing with it and similar absurdities, "(i.e. a quantity that can never be attained or measured) is a mathematical concept that cannot occur in the real physical universe." Your essay has many posts and I did not immediately see an answer to it. Most of the criticisms against you are flawed and tiresome to read, probably even more so to respond to all of them.

My statement on microstates, macrostates and multiplicity was what I wanted you to focus on when reviewing my essay. In fact those three ideas are the foundation of my use of derangements. I'm glad that you had a question about time occuring when something is not "interacting" I had much trouble with this. I think the partial derangement in the essay may satisfy your question. Partial derangements also provided the macrostates. I know you are busy and it is appreciated that you skimmed it.

Roger Penrose is partially responsible for the approach I used. I attended a colloquium of his sponsored by my university. I had problems with his use of entropy in quantum mechanics. He used quantized "blocks" for space-time with entropy in terms of volume. He concluded that something is wrong with time and increasing entropy because his "blocks" would become smaller. I was able to ask how he accounted for the Planck length and increasing smaller intervals created by his entropy equation. His answer was, "we need a new understanding of time". My second question to him was if he would be able to donate a copy of his book, "The Road to Reality" to a poor undergrad. He replied, "it will be in paperback soon". If you personally know him please tell him I just read it at the book store.

The finite number of possibilities in your evolving probabilistic block makes me think of the saying, "a chip off the old block." I believe you will shift the paradigm.

Best of Luck,

Brian Beverly

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Dear George,

You wrote (Dec. 15, 2008 @ 15:22 GMT):

"The current topic is The Nature of Time. I am not interested in a debate on the nature of gravitational energy. Please save us both a lot of bother by desisting this series of postings."

Since you haven't so far found some spare time to answer any of my postings at your thread, may I explain the reason why I respectfully invite you to discuss the nature of gravitational energy as 'the proof of the pudding' for your EBU hypothesis (as well as BU hypothesis in C. Rovelli's "forget time" proposal).

It is well known from GR textbooks (cf. MTW, p. 467) that there are inherent difficulties in defining energy in GR, due to its so-called non-localizability (cf. L. Szabados). Once we introduce Lorentzian metric, we're incapable of capturing the *quasi-local* nature of energy in GR from the outset. There is nothing quasi-local in splitting the spacetime, as in ADM hypothesis, either.

The proponents of BU (Rovelli, Barbour, etc.) can 'sweep the garbage under the rug', because the frozen "block" of spacetime cannot encapsulate any quasi-local object, in neither time nor space. This is a kind of Stalinist approach -- kill the time, kill the problem.

But since you claim that can do better, by proposing an Evolving Block Universe (EBU), I will greatly appreciate your professional explanation of how you tackle the problem of quasi-local -- in time -- energy in GR.

To be specific: You acknowledged (Dec. 17, 2008 @ 12:54 GMT) that cannot offer an answer to the question of "why does the arrow of time of quantum theory (related to collapse of the wave function, see for example The Emperor’s New Mind) coincide with the cosmological one (determined by large scale statistical considerations of a classical kind)?"

Perhaps you can't answer this question because (i) there is no such thing as "arrow of time of quantum theory", as the "collapse" may be an artifact from our incomplete presentation of the dynamics of quantum systems (cf. the first posting to your thread, from Dec. 2, 2008 @ 07:02 GMT), and (ii) the cosmological time arrow encapsulates the quasi-local nature of gravitational energy, which you seem to be very reluctant to discuss.

Please put your cards on the table: there is very little quasi-local time left to the contest ending on January 1, 2009.

Thank you very much in advance.

Dimi

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Dimi & George,

In cosmology there are no Killing vectors defined globally. A metric with a scale factor R(t) will resist the imposition of a global Killing vector. This means that there is no universal time "vector field," for lack of a better term at the moment, which connects up spatial surfaces. It also means there is no isometry which which defines a K*E = const. So in cosmological relativity it appears that time is a local parameter, as is potentially energy conservation.

The nonlocalizability of energy Dimi mentions comes about because while one has a momentum-energy tensor T that obeys a continuity equation nabla*T = 0, this gives funny results for momentum-energy localization. For a basis element e which gives p = e*T (here indices are supressed and p can be momentum or energy). We might put a Gaussian surface around a region containing that p and integrate it but Stoke's law tells us that

int_(S}p ds = int_{vol} nabla(e*T)dv

The rub comes in because there is a nabla*e which emerges that determines a connection coefficient in general. The volume and surrounding area of space or spacetime where p is defined is evolving or a part of the field. So different observers will find different results.

Lawrence B. Crowell

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On reviewing whathas been going on, itseems ot me that the essays and postings on the various threads in this forum on the Nature of Tme have one marked divergence: that between solidly scientifically based approaches, and others that are more philosophically based. I have been considering what one might try to say that links the two to some degree, with the following result:

The nature of...

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To Dimi Chakalov:

I respond to postings that raise questions I find interesting and relevant to the topic under discussion. I do not respond to postings that try to tell me what I should do, and (apart from fqxi essays) I feel no obligation to read any matter on any webpages linked to any postings.

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To George Ellis

My support for your 3rd point of view can be put in question by

- Refutation of my admittedly unwelcome criticism

- Confirmation of the standard model by means of LHC

- Quantum computers as promised

Please find attached part 2.

attachments: 1_Microsoft_Word__How_do_part_2.pdf

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Dear Lawrence B Crowell

there may not be a timlike Killing vector field, but there is a conformal timlike Killing vector.

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Dear George,

You seem to have real difficulty acknowledging, when, or even the existence of, an argument which directly contradicts something you have said. Hourglasses were not designed for putting one's head in George.

Best wishes

Peter

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Dear George Ellis,

Thank you for the helpful summary of the presented views on time and for your comments on them. And, of course, we are all thankful to FQXi for providing this opportunity. If the discussions on the forums here are not kept permanently online, I think a volume with selected and edited posts (views) can be considered for publication.

Let me give my views too which do...

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attachments: 1_Growing_4D_World.pdf

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Dear Peter Lynds

I thought I had already adequately acknowledged that your and my positions differ. If not, here it is: I acknowledge that you have arguments that directly contradict what I have said. However the disagreement is philosophical rather than one based in empirical scientific issues, and you have no papal or other authority to impose your philosophical position on anyone else. ...

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Dear Peter Lynds

I thought I had already adequately acknowledged that your and my positions differ. If not, here it is: I acknowledge that you have arguments that directly contradict what I have said. However the disagreement is philosophical rather than one based in empirical scientific issues, and you have no papal or other authority to impose your philosophical position on anyone else.

In regard to your philosophical position: you state "Given that, whether one believes in them or not, the past, present, future, instants etc, are non-material, there can be no "rationally supported and scientifically based" foundation for them in physics." I disagree. A lot of modern physics is about immaterial entities: for example the electromagnetic field and the spacetime metric. Indeed one view from quantum field theory denies that particles really exist: it is only fields that are real, on that view.

You continue "I was talking about faith in the physical existence of things that are non-material, i.e. do not actually have any physical existence!" That sentence is a tautology because of the word "physical". If you try a more sensible version: "faith in the existence of things that are non-material", then my position is very clear: certainly such things have a demonstrable existence. Example: thoughts exist but are immaterial. What is my criterion for existence? An entity exists if it has demonstrable causal effects on the world of particles and material entities; thoughts indeed have such effect (for example the computer you are using exists because of the causal efficacy of human thoughts).

You state "while brain processes are governed by the laws of physics, there is no reason why such processes cannot create the experience of a present moment. Indeed, I think the brain does do this, and as I've already alluded to, I think this holds the key to understanding how conscious awareness in possible." Yes indeed I agree; but that position is not consistent with a Block Universe view of spacetime which excludes the flow of time at all scales, for then the brain processes that lead to such experience cannot take place, as *nothing* actually takes place on that view, where the present is indistinguishable from the past and the future and all of existence just is.

Finally you emphasize your position thus: "as long as one recognizes that instants, instantaneous magnitudes, space-time points etc, do not exist [....]" This stance places you at loggerheadsa with virtually all other postings on this forum. You are entitled to that philosophical position, but you should recognise that it is not shared by almost anyone else taking part in this debate, and I repeat that you have no authority to impose it on anyone else.

Actually as I have stated in various places, and thought I had stated here, I am agnostic about whether both the BU and the EBU are epistemological or ontological in nature: the argument is about whioh description gives the more accurate view of reality, whatever one's position on the ontological issue regarding the nature of the BU and the EBU.

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Dear Vesselin Petkov

Thank you for the carefully considered further discussion. I have to confess however that I find what you say quite puzzling: you seem to acknowledge an EBU can fully explain the experimental evidence, and then you say the evidence contradicts the EBU. I don't follow that.

In more detail: you say

"1. Let me start with what you wrote "It follows that all...

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My last posting got cut off. Please add at the end: Good, at least we agree on this.

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On Dec. 19, 2008 @ 21:15 GMT, George Ellis wrote:

"To Dimi Chakalov:

"I respond to postings that raise questions I find interesting and relevant to the topic under discussion. I do not respond to postings that try to tell me what I should do, and (apart from fqxi essays) I feel no obligation to read any matter on any webpages linked to any postings."

1. Given the lack of professional response to any of my postings on your thread, it seems to me that you do not find the issues raised by me "interesting and relevant to the topic under discussion". You failed to explain which particular issues raised by me were not relevant, however.

2. I was not trying to tell you what you should do, George.

I was quoting from your statements for the sole purpose to show you that they are not better than those produced by your colleagues supporting the "block universe" viewpoint.

I only wanted to help you do better than your opponents. For example, I mentioned your notion of finite infinity from 1984 (Dec. 15, 2008 @ 18:44 GMT), which I believe can be updated and improved, if only you could sort out the tasks set by you: check out the quotes from your numerous postings above (Dec. 16, 2008 @ 14:43 GMT).

3. The fact that you "feel no obligation to read any matter on any webpages linked to any postings" is very sad, in my opinion. As you acknowledged (Dec. 3, 2008 @ 16:47 GMT): "I have puzzled over the Conway-Kochen 'Strong Free Will Theorem' paper, without really understanding what if anything it has to do with free will".

If you follow the link in my first posting (Dec. 2, 2008 @ 07:02 GMT), I suppose you will understand the crux of Conway-Kochen argument. If not, it will be entirely my fault, so please write me back with your specific questions.

Wishing you and all colleagues at this forum a very merry Christmas,

Dimi

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George,

Agreed that under conformal factors the cosmology reduces to a Minkowski spacetime, and so the conformal factor defines conformal killing vectors on a cosmology. There is a subtle issue IMO about the topology of the cosmology, so if the cosmology is a spatial sphere conformal time appears conformally equivalent to flat time "modulo" either one point or any loop or orbit around that point.

To throw in my bit about the cases 1, 2, 3, I agree that #1 is not realistic. I find it hard to imagine how my little brain and everyone else's little brain somehow manages to construct this illusion called time. When it comes to #2 and #3 I am somewhat between them. I do think it is likely that time on the micro-level may not exist as we think of it, but I suspect the same is the case with space as well. In my approach with noncommutative groups in associator rings space and time are similar to Sakharov's notion of pregeometry. What we think of macroscopically as space and time emerge due to coarse graining over these elements on a large scale.

Lawrence B. Crowell

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Dear George Ellis, I am pleased that you distinguish three viewpoints rather than the two that some people recognise. My viewpoint is closest to your viewpoint 2 which, as I said, is different from e.g. Julian Barbour who is closest to your viewpoint 1. It is a worthwhile distinction

Your objection to viewpoint 2 is that it is difficult to see how it can be made to work. I would just say that at this time we do not have a full theory of quantum gravity despite much effort, so this has already proven to be a diffcult task. Demonstrating the emergence of time in a convincing way is likely to require much if not all the understanding that a theory of quantum gravity provides. Therefore the fact that the emergence mechanism is difficult to see at present is not a strong argument against its possibility.

Nevertheless, those of us who support this view use analogies where (for example) time and space emerge from discrete pregeometric theories in the same sense that thermodynamics emerges from the kinetic theory of gases. These may not be the complete and final solution but they do give plausbility to the concept of emergence.

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Phil, I fully agree with you (Dec. 20, 2008 @ 13:20 GMT) that "the fact that the emergence mechanism is difficult to see at present is not a strong argument against its possibility".

Wouldn't it be better if we start with the basic unresolved issues in QM (the measurement problem & STR) and in GR (the quasi-local gravitational energy)? George seems to be reluctant; hope your attitude is different.

Dimi

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Larry, you claim (Dec. 20, 2008 @ 13:17 GMT) that "under conformal factors the cosmology reduces to a Minkowski spacetime, and so the conformal factor defines conformal killing vectors on a cosmology."

There is a crusial issue IMHO regarding the physical time evolution in FRW cosmology: see the quote from Thomas Thiemann's astro-ph/0607380 v1 at, in my posting (Dec. 13, 2008 @ 20:55 GMT) at

Gavin Crooks's thread.

Dimi

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Dimi, I think it is healthy that we all have different ideas about what are the important issues are, and what are the best ways to treat time etc. It is fun and useful to discuss the relative merits of our preferred philsophical approaches, but the only way to determine who has the best idea is to see how far they take us towards a well formed theory and learn from the results.

Like many others I do not worry about the measurement problem when I try to think about quantum gravity because I dont think quantum gravity will solve it. I dont have a solid reason to believe that so I could be wrong, but I dont have time to try out every possibility. I am happy that there are others who think differently so that approach wont be neglected.

On the subject of gravitiational energy, a few years back I worked through a direct application of Noether's theroem to derive the covariant form for the energy conservation law in GR. I deposited the result in the arXiv at http://arxiv.org/abs/gr-qc/9701028. There is a lot that can be said about the nature of the solution but again I am not left with any particular issues that I think are of significance to quantu gravity. Perhaps someone else will be able to derve a useful clue from such considerations but that wont be me.

The best thing I can say is that you should also seek out those with the most similar ideas to yours because you will learn more from them than from people who are trying a different direction.

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Phil, thank you for pointing out your arXiv:gr-qc/9701028v3, in which you wrote (p.9): "We are now in a position to consider the case of energy in a closed cosmology." Your manuscript appeared well before the advent of the "dynamical dark energy" (DDE), and I can't find any clues as to how one could include DDE in some 'closed cosmology'. Please advise.

I also appreciate your advice "you should also seek out those with the most similar ideas to yours because you will learn more from them than from people who are trying a different direction", and am I indeed following it, at my web site.

The reason for my postings here is this. Suppose you, George, Carlo, and all the rest on this Forum, myself included, were collecting different paper items, just as a hobby. If I was collecting paper napkins, while you and George were collecting bottle labels, then of course I cannot pursue you to switch to my hobby, nor the other way around.

I am definitely certain this is not the case, and I will patiently wait for the professional response from George Ellis, by January 1, 2009. I can't miss this unique opportunity, since his opinion is very important to me, and I am definitely certain that he does not treat theoretical physics as some hobby.

Dimi

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Dimi, Given an invariant lagrangian for the DDE you could apply Noether's theorem in the same way. The derived total energy for a closed cosmology would still be zero.

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Phil, "an invariant lagrangian for the DDE" (Dec. 20, 2008 @ 19:21 GMT) presupposes some theory of quantum gravity, which would treat the energy density of the quantum vacuum -- the first choice for cosmological "constant" -- in the framework of such brand new quantum gravity. Perhaps it is a better idea to start with some far more modest task, such as George Ellis' finite infinity proposal from 1984, and see where we will end up. What do you think?

Dimi

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Dear George,

Thanks for your comments. I see it as a step forward, so I appreciate that. Thanks. I see that it sort of comes with an out-clause, however, as you seem to now want to dismiss my arguments (and the contents of my essay) as philosophy.

As my essay deals with questions of the existence of time, instants, instantaneous magnitudes, space-time etc, a lot of it naturally is of...

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Dear George Ellis,

Thank you for the helpful and constructive discussion. Let me (i) clarify what puzzled you in my previous post, and (ii) summarize the arguments for and against the BU and the EBU and see whether you would agree. I believe such agreements are crucial for any advancement especially in fundamental physics.

1. I think you were puzzled because of our different views on...

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Dear Vesselin,

With the quotes you mentioned, I think you are confusing the lack of differentiation between past, present, and future in relativity/times all being mapped out together (the central feature of the block universe resulting from the lack of absolute simultaneity), with the view that the block universe means that change and even our "sense" of the flow of time are illusions. I do not think that any of the quotes are referring to the latter. I'm happy to also find myself in a position where I can completely agree with George about something really significant and pertinent! (i.e. that such a view is completely incompatible with not only observation, but all reason too. Indeed, I think that so many people accept it is truly bizarre). In connection to this matter and the BU vs. EBU, if you have possibly been following my discussion with George, you will be aware by now that there is a third option (i.e. lack of absolute simultaneity/BU compatible with change).

Best wishes

Peter

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Dear Dimi Chakalov

In my view the key unsolved problem in classical General Relativity Theory (GRT) is not gravitational energy, it is the definition and nature of gravitational entropy, and the related issue of coarse graining in GR.

Issue 1: Gravitational entropy and gravitational attraction

Almost all the statements usually made about entropy and the second law of...

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Dear Vesselin

I don't have time to give a detailed response to your last posting now, and indeed may not manage it before time is up as I depart for overseas tomorrow. However there is one paragraph in your reply I must comment on.

You state "I definitely agree with you that "physics should be able to describe the real world" and what we have been discussing is precisely the question "What is the real world according to relativity?" So, the very question is what is the real world. I think we have to be very careful not to take for granted a given view of the world and then say the physics should be able to describe that specific picture of the world." If you exclude from the real world the experiences of ordinary every day life, then you and I have completely incompatible philosophical views. It is that world of ordinary every day life that I wish to at least partially explain through my understanding of physics.

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Dear George Ellis,

Your receny response post covered response to my query partly. i feel satisfied as i noticed a rationality in your response coupled with frankness and humility too. When one discuss 'established'concepts that like of space and time, one need not quickly jump to discard one or the other merely on the basis of an alternate concept explaining some phenomenon in Physics well. It is the totality of Physics that needs to be kept in mind. i agree when you indicate that an alternate approach can well appear to explain black holes behaviour than the present necessity to consider quantum nature of Gravity. If one looks at personal views of einstein and some other scientists of recognized authority, quantum mechanics may well be considered to provide explanations for the phenomena of atomic/nuclear and particle physics, the macro-level physics demand by the unique behavior of black holes may well find an alternate explanation from other than quantization of gravity. Garvity is the first interaction that the Universe has seen to emerge, followed by strong nuclear , e.m. and the weak nuclear. These all followed the demands of nature as the universe evolved. It is quite possible that gravity has some uniqueness we still need to identify that makes its union with a unified field difficult in the present day Physics.

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George,

Four hours ago (Dec. 21, 2008 @ 12:55 GMT), you wrote: "It is that world of ordinary every day life that I wish to at least partially explain through my understanding of physics."

Then please do not ignore the first posting to your thread, and the rest of my comments and critical remarks.

I understand that you're leaving for overseas tomorrow. Wish you a nice journey, and hope to hear from you when you come back to your office. Please try, at least once, to reply professionally.

Dimi Chakalov

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Dear Vesselin Petkov

one further important point I will briefly raise regarding your last post: the EPR and Aharanov discussions are all based on the Schroedinger non-relatistic equation. There is therefore no reason whatever to expect their results to be compatible with Special Relativity ideas and effects, indeed it would be extremely odd if they were. The Dirac equation was developed precisely in order to extend the analysis of the Schroiedinger equation to be compatible with special relativity theory.

So please note that an EPR type argument only has a chance of becoming decisive in the present context of debate when it is based on the Dirac equation, not the Schroedinger equation. When you mix relativity based arguments with effects coming from the the Schroedinger equation, you are mixing incompatibles.

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Dimi Chakalov

please explain carefully to me what was unprofessional about my posting of Dec. 21, 2008 @ 12:42 GMT.

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With general relativity the Lagrangian for the motion of a particle is mc^2 int ds, where ds is the invarant interval. The action, would in general be Lds = pdq - Hdt, if we think of there being potentials and the like. This is a curious thing, for the action of GR motion including potentials, or mc^2 = k^2 - E^2 etc with DG equations, then we have an intertwiner between the proper time s and...

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Dear Peter,

I am not confusing anything. We have been talking about what the real world is (not about descriptions) - what you separated as two things is the same BU view. On this view, which follows from relativity of simultaneity and the other relativistic effects, the world is not separated into past, present, and future, which means that it is a forever given four-dimensional block...

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Dear Peter,

I am not confusing anything. We have been talking about what the real world is (not about descriptions) - what you separated as two things is the same BU view. On this view, which follows from relativity of simultaneity and the other relativistic effects, the world is not separated into past, present, and future, which means that it is a forever given four-dimensional block with no motion in it (since the *macroscopic* physical objects there are a network of worldlines, or rather worldtubes).

What you wrote "that such a view is completely incompatible with not only observation, but all reason too" is plain wrong. The only explanation for such a claim could be the fact that you have been conveniently ignoring (let me stress it) the *irrefutable* arguments that the relativistic effects discussed here would be impossible if the macroscopic physical bodies were *not* worldtubes. On the BU view these worldtubes are entirely given, whereas on the EBU they are growing.

Now let me invite you to prove your claim by considering *experiments* (ultimately, the only thing that can confirm or refute a claim) not philosophical considerations:

1. See in Sec. 3 of my post of Dec. 17, 2008 @ 05:47 GMT the thought experiment version of the real experiment that confirmed length contraction. Try to explain whether the length contraction of a meter stick at rest in observer A's reference frame would be possible if the worldtube of the meter stick did not exist. More specifically, whether observer B (moving relative to A) would measure A's meter stick as a different three-dimensional meter stick whose different parts are green, red, blue, whereas A measures a red meter stick.

At this moment it appears that such experiments cannot rule out the EBU since both - BU and EBU - explain length contraction as a manifestation of the reality of the meter stick's worldtube. But since BU and EBU represent two drastically different worlds it is clear that other experiments should be considered in order to rule out one of the competing BU and EBU. Such an experiment, I think is the following.

2. The EPR-experiment described in my post of Dec. 20, 2008 @ 04:39 GMT (and the diagram there):

"Now, consider the following (I think serious) situation. Let events (P_B) and (Q_B) on the same diagram be the measurements of the two photon polarizations in an EPR experiment. And let (P_B) be the experiment that determines the outcome of (Q_B). So, on the EBU view, what is measured on (Q_B) has been determined by an event that has not yet come into being!? I hope, you now understand one of the reasons of why I have difficulty accepting the EBU view."

Can the future influence an experiment if the future does not exist? And it exists only in a BU. You can also test the "third option" you mentioned in view of the above experiments.

When you understand just these two arguments based on *experiments* specifically designed to test theoretical predictions of physical theories (not on observations directly taken from our daily experience) you should at least stop claiming "I think that so many people accept it [the BU} is truly bizarre". The very fact that so many people accept it should have made you seriously ask yourself "Why?"

Vesselin Petkov

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George Ellis wrote (Dec. 21, 2008 @ 17:30 GMT):

"Dimi Chakalov

"please explain carefully to me what was unprofessional about my posting of Dec. 21, 2008 @ 12:42 GMT."

You ignored my critical remarks -- all of them.

You wrote (Dec. 21, 2008 @ 12:42 GMT): "In my view the key unsolved problem in classical General Relativity Theory (GRT) is not gravitational energy, it is the definition and nature of gravitational entropy, and the related issue of coarse graining in GR."

I respect your viewpoint, but please notice that you completely ignored all critical remarks in my posting from Dec. 16, 2008 @ 14:43 GMT.

You also wrote (ibid.): "These (pseudotensor definitions - D.C.) have not yet been used to give a satisfactory definition of gravitational entropy, as far as I am aware."

Perhaps because it isn't possible to explain one mess (pseudotensor definitions) with another one (gravitational entropy).

I am not aware of some precise definition of 'low geometric entropy', but if we trust the calculations by Penrose (cf. Singularities and Time-Asymmetry, in General Relativity: An Einstein Centenary Survey, ed. by S W Hawking and W Israel, Cambridge University Press, 1979), it seems to me that the initial gravitational entropy had to be *as low as possible*, which in turn means that we cannot begin by assuming a FRW form for the metric -- even approximately.

See Slide 3 from R. Penrose's talk "Before the Big Bang?" (7 November 2005) here.

Big mess. Which is why I asked you to get to the bottom of this 'gravitational energy' and its quasi-local -- in time? -- nature.

But again, the main puzzle in your EBU idea are produced by your own statements, as quoted in my posting from Dec. 16, 2008 @ 14:43 GMT above. As you acknowledged (George Ellis, Dec. 4, 2008 @ 10:00 GMT):

"So a key element is how proper time relates to coordinate time as we move to the future, ... "

If you believe can resolve this 'key element', please test your solution with the problem of gravitational energy, from 1918.

Thank you for your (quasi-local?) time.

D.C.

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Dear Prof George F R Ellis,

Increase in the inertial mass and the time dilation in the special theory of relativity are simple kinematic effects. These effects in the essay The Theory of Time, Space and Gravitation are a consequence of the gravitational action. Both physically and philosophically it is more suitable.

Yours faithfully

Robert Sadykov

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Dear Colleagues,

I'm afraid we've been tearing apart George Ellis with our very diverse questions. I for one wish to apologize to George for my violent curiosity.

Perhaps we can put aside our questions, and focus on one issue, which I believe is the crux of his EBU proposal:

I look at my wristwatch, and record some linearized variable called 'coordinate time'. How does my wristwatch read it, given the premise that any finite interval from it belongs to the cosmological time?

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Dear Vesselin,

Thanks for your comments.

"On this view, which follows from relativity of simultaneity and the other relativistic effects, the world is not separated into past, present, and future, which means that it is a forever given four-dimensional block with no motion in it (since the *macroscopic* physical objects there are a network of worldlines, or rather worldtubes)."

Again, if you had perhaps been following my discussion with George you will be aware that I do not think that the last 4 words of your sentence ending before the brackets need apply to the BU (I will get to worldtubes shortly). That is, if interpreted correctly, the BU is not incompatible with motion and change, and this can be seen to be a separate issue from the lack of absolute simultaneity. Moreover, I do not think that any of the quotes you provided refer to this issue (lack of change). They are all direct references to the lack of differentiation between past, present and future in relativity/all times being given and laid out. I'm pretty sure that there are no quotes by Einstein saying that motion and change are illusions. One will find a small handful of ones saying that space-time and time and space have no physical existence though.

"you should at least stop claiming "I think that so many people accept it [the BU} is truly bizarre". The very fact that so many people accept it should have made you seriously ask yourself "Why?""

Considering that I was referring to the standard interpretation of the BU (no motion, no change), but clearly accept lack of absolute simultaneity and the BU compatible with motion/change, I don't really appreciate your inserting the bracketed BU above.

In relation to worldtubes, I have by no means been "conveniently ignoring" your argument. Although I disagreed with it, I did not see it as representing a direct challenge to mine. In relation to worldtubes, though, although bodies can naturally be described as 3 dimensional (any massive body will be by default), and they can move (4-d, and because continuity, including the rotation of the hands of a clock, can be shown to simply be the result of the capability for motion in Nature, this dimension needn't be called time), worldtubes do not exist. Moving bodies do, and this is all that relativity requires. If your thought experiment holds, I think this is simply what it shows. That is, I think you are misappropriating the existence of 3-dimensional dynamic bodies with the existence of worldtubes.

Best wishes

Peter

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Dear George Ellis,

Thank you for your quick comments and have a safe trip and all the best for the holidays and the coming 2009. I will also reduce my postings here since a very important deadline in January is fast approaching and I will have to do most of the work before the next semester, which starts here on 5th of January.

I will briefly comment only on this sentence: "If you exclude from the real world the experiences of ordinary every day life, then you and I have completely incompatible philosophical views."

In any case you will have the paper (on the debate BU vs EBU) based on my talk at the third spacetime conference in Montreal last June. I believe it will be published, which will make it available for criticism. Every winter semester I have been teaching a course on space and time and this year the present debate will be even more emphasized.

I do not think we "have completely incompatible philosophical views." You take for granted that "the experiences of ordinary every day life" can be explained and understood only in terms of an objective flow of time. As the stakes are at the highest possible level - our view of reality - I do not like to take anything for granted. All (even purely logical) options should be on the table.

We have nothing to lose if we do that, but we may have a lot to lose if we do not do it. Then rigorous analyses of all relevant or potentially relevant *experimental* facts confirming predictions of the modern physical theories should tell us what is the dimensionality of the world (at least according to relativity) and whether *macroscopic* bodies are completed or growing worldlines (or rather worldtubes since those bodies are spatially extended objects). That is why, in my postings here I have tried to concentrate only on experiments; in line with that I had in mind the real EPR *experiments*; so I have not mixed anything.

Vesselin Petkov

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Dear Peter,

Let me propose something that I think is both constructive and fair - publish your objections against the BU view. If you do not wish to criticise other people, you are welcome to criticise my position - you can choose some of my publications on the BU view and start with them. Then I will be able to respond.

Despite that I have followed the debates on this forum I have failed to see your arguments; to me, any of your claims was supported by another claim. For instance: "If your thought experiment holds, I think this is simply what it shows. That is, I think you are misappropriating the existence of 3-dimensional dynamic bodies with the existence of worldtubes." I do not see an argument here - just claims.

Since I guess you may disagree I think the fairest thing is to publish your arguments and prove me wrong.

All the best for the holidays,

Vesselin Petkov

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Dear Vesselin,

Thanks. In relation to my arguments, and although the BU vs. change issue isn't the main focus of it, you really just need read my essay (and notes).

All the best for Christmas too. If you possibly see this George, all the best to you as well.

Peter

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On Dec. 22, 2008 @ 01:55 GMT, Vesselin Petkov wrote to Peter Lynds:

"Let me propose something that I think is both constructive and fair - publish your objections against the BU view."

The BU hypothesis suffers from an incurable logical error: Non sequitur.

Neither STR nor GR can detect the Heraclitean flow of time, because the latter is supposed to *emerge* along with the *emergence* of 3-D space. These unresolved issues are clearly outside the applicable limits of GR.

If the flow of time were some 'observable in GR', there should be some kind of material content left from it as 'observable in GR', and Einstein’s field equations (EFE) would NOT guarantee "the conservation of total energy-momentum": see Eq. 2 in [George F R Ellis and Henk van Elst, arXiv:gr-qc/9812046v5], and notice that it is valid only if the cosmological constant [lambda] "is constant in time and space" [ibid.]

R. Penrose explicitly stressed (The Road to Reality, p. 777) that "any non-constancy in [lambda] would have to be accompanied by a compensating non-conservation of the mass-energy of the matter."

It should be agonizingly clear that GR cannot address these "dynamic dark energy" (DDE) issues of the Heraclitean flow of time. If GR could detect DDE as some Dirac observable, the latter would make the *perfectly smooth* DDE 'observable in GR', and the ether would come back.

Any definite statement about the flow of time, derived from STR and/or GR, is logically inconsistent. GR is still too "far away" from quantum gravity and quantum cosmology.

If you claim that 'fish cannot ride bicycles, therefore we should "forget" about bicycles', you will make the same logical error, non sequitur. C. Rovelli, J. Barbour, and many other people already made it in their publications.

If you, Peter, or anyone else at this forum cannot understand the text above, it will be entirely my fault, so please don't hesitate to ask questions. Then please tell your students all about the logical error in BU: kids have the right to know everything we know. I hope you all agree.

D.C.

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This will be my last posting, for a number of reasons: I believe I have said all I have to say, and my postings are now in effect just repeatng what I have already said. There are a number of different positions held by different people making postings on this thread; they have been adequately expressed, and are apparently not going to change. At the root are philosophical rather than scientific...

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This will be my last posting, for a number of reasons: I believe I have said all I have to say, and my postings are now in effect just repeatng what I have already said. There are a number of different positions held by different people making postings on this thread; they have been adequately expressed, and are apparently not going to change. At the root are philosophical rather than scientific differences; those philosophical positions shape the scientific discourse, but are not themselves testable.

I am also ceasing because I am tired of the level of aggression that is apparent in some of the postings, combined with a considerable lack of humility. The essayist who answers postings on this forum is exposed to a considerable degree of unpleasantness if they continue answering: so why should they do so? Carlo stopped answering a long time ago, I suspect for this very reason.

My last substantial comment is the following: my very useful debate with Vesselin has brought out into the open a key issue as regards how we do science. He states

"You take for granted that "the experiences of ordinary every day life" can be explained and understood only in terms of an objective flow of time. As the stakes are at the highest possible level - our view of reality - I do not like to take anything for granted. All (even purely logical) options should be on the table." I agree.

Vesselin continues "We have nothing to lose if we do that, but we may have a lot to lose if we do not do it. Then rigorous analyses of all relevant or potentially relevant *experimental* facts confirming predictions of the modern physical theories should tell us what is the dimensionality of the world (at least according to relativity) and whether *macroscopic* bodies are completed or growing worldlines (or rather worldtubes since those bodies are spatially extended objects). That is why, in my postings here I have tried to concentrate only on experiments; in line with that I had in mind the real EPR *experiments* ". It is the "only" which I simply cannot accept. Yes we must take into acount rigorous scientific exsperiments; but I regard all of ordinary life also as an "experiment" revealing important aspects of the nature of the world and the universe. Indeed the mind works by a process of making and testing hypotheses about the way the world around us functions; this is made explicit for example in the book "On Intelligence"by Jeff Hawkins. We have to subject that daily experience to rigorous anaysis, as it is well known that our senses and understandings can deceive us, but nevertheless in the end they are all we have; they are in particular what we rely on as we do scientific experiments.

Furthermore, as I have stated, above, I wish to understand how science underlies ordinary daily life, and one can hardly do that on a philosophical basis that excludes as evidence the nature of that ordinary daily life. There is a real problem with scientifically based treatises that take that stance, and then proceeed to make magisterial statements about the nature and meaning of life, as often happens. If one wants to understand the full depth and nature of ordinary life, including its relation to its scientific underpinnings, one must take into account *all* the evidence: and in particular one must take as evidence the way our daily life experiences can occur.

The upshot is that I regard the experience of daily life as conclusive evidence about the nature of spaceetime: if one's theory does not adequately explain this as well as the full range of scientific experiments, one should go back to the drawing board. The scientific basis needs to be rexamined to see how it can be developed so as to be compatible with ordinary life experience, as well as with the scientific experiments.

Happy Christmas to all.

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This is my first and last reaction to your never ending posts. It seems you never try to understand what the other people write. In this sense I admire George Ellis for his enormous patience with you.

You even quoted above what I suggested; so follow it. If you really think you have something to say professionally, publish it and you will have my answer.

Vesselin Petkov

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The first part of my posting (above) was not displayed - that is why I am posting the text again.

______________________________________

Dimi Chakalov wrote on Dec. 22, 2008 @ 04:51 GMT

On Dec. 22, 2008 @ 01:55 GMT, Vesselin Petkov wrote to Peter Lynds:

"Let me propose something that I think is both constructive and fair - publish your objections against the BU view."

The BU hypothesis suffers from an incurable logical error: Non sequitur.

______________________________________

This is my first and last reaction to your never ending posts. It seems you never try to understand what the other people write. In this sense I admire George Ellis for his enormous patience with you.

You even quoted above what I suggested; so follow it. If you really think you have something to say professionally, publish it and you will have my answer.

Vesselin Petkov

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Vesselin Petkov wrote (Dec. 22, 2008 @ 06:02 GMT): "If you really think you have something to say professionally, publish it and you will have my answer."

About twenty years ago, I had a long discussion with two members of Jehovah's Witnesses, and because it was going nowhere, I asked them to formulate the conditions under which they will accept my viewpoint and convert to Catholicism. Never heard from them.

But since Vesselin Petkov is doing science, and is responsible for teaching students (=kids), I respectfully ask him to formulate the conditions under which he will accept that the "block universe" (BU) viewpoint is indeed logically inconsistent, being formulated on the logical error 'non sequitur'.

To the best of my knowledge, Carlo Rovelli and Julian Barbour haven't done it. In the context of the fish & bicycles metaphor (cf. my posting from Dec. 22, 2008 @ 04:51 GMT), they propose to "forget" bicycles, but fail to acknowledge that the "sea" has to have some kind of "boundaries" which nobody has so far managed to *derive* from the "sea" alone (references available upon request).

Stated differently, the first off task toward rejecting the Heraclitean flow of time is to show rigorously the "boundaries" of spacetime. If you can't solve it, you have no logical grounds to expand the applicable limits of STR and GR, and speculate about some "block universe".

Please put *your* cards on the table, and also promise that if I prove BU logically inconsistent, you will tell your students all about it -- kids have the right to know everything we know.

I wonder if you have the guts to do it. You will be the first person to receive my manuscript.

If you can't meet this requirement for scientific research, please note that I am too tired to discuss issues based solely on faith and emotions.

D.C.

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George Ellis wrote (Dec. 22, 2008 @ 05:42 GMT):

"There are a number of different positions held by different people making postings on this thread; they have been adequately expressed, and are apparently not going to change."

Please exclude me from this set of people who "are apparently not going to change." I am ready to change my viewpoint, and am flexible enough to accept yours, if only you can make it clear by responding to my critical remarks, hence convince me that I got it wrong.

Merry Christmas to you and all participants in your forum.

D.C.

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Dear George and Dimi Chakolov,

Firstly, George, I enjoyed your essay very much - and many of the comments you have contributed in this forum - since as always you put your finger on the essentials. Indeed, my viewpoint on the nature of time accords very much with the evolving block universe idea you put forward, as you are probably already aware. I understand that you won't be contributing...

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Dear George and Dimi Chakolov,

Firstly, George, I enjoyed your essay very much - and many of the comments you have contributed in this forum - since as always you put your finger on the essentials. Indeed, my viewpoint on the nature of time accords very much with the evolving block universe idea you put forward, as you are probably already aware. I understand that you won't be contributing more to this forum; and I think the correspondents here have been extremely lucky to have had you give so generously of your time, and to have exercised such a degree of patience. I think that in itself deserves a prize.

My other reason for this post is to address Dimi Chakolov, who has been pestering you quite excessively here. Dimi: the subjects you raise are ones that are treated to some extent in my essay, though for more details, such as my working definition of finite infinity you will have to look at my paper Cosmic clocks, cosmic variance and cosmic averages, New J. Phys. 9 (2007) 377. I believe that the subject of gravitational energy, and its quasilocality - a consequence of the equivalence principle - is indeed important for a detailed quantitative understanding of the nature of time on cosmological scales.

I agree with George on almost every point, and in particular with his reply to you of December 21 in which on he identified the key unsolved problems of general relativity as being the definition and nature of gravitational energy and the related issue of coarse graining in GR. The only place where I differ somewhat is that contrary to some of George's statements under "3. Gravitational entropy and gravitational energy", it is my view that a successful quantitative description of gravitational entropy, which fully deals with coarse graining in GR, will necessarily entail a first law of thermodynamics. A first law must relate the difficult notion of gravitational entropy to the difficult notion of gravitational energy. While one can legitimately try to approach the problem other ways, as George suggests, I think any of these approaches can only work if they confront the issues raised by the "phenomenological approach" since the equivalence principle and general covariance are the core concepts of GR.

The fundamental unpredictability of quantum mechanics, and its consequences as depicted in Figure 1 of George's essay, are an essential justification for the EBU. Equally important for any approach to coarse graining in this context is the fact that GR is a causal theory. The geometry in a region near any event can only depend on events within the past light cone at that event: the events which have been made real among past possiblities and have actually occured within the finite realm of that evolving block. Regions of the universe which are not in causal contact evolve independently until they come into causal contact, and then some process of self-averaging takes place as the domain of the causal past increases. Rather than assuming a simple exact geometry for the whole universe (whether a single solution of cut-and-paste exact solutions), it is my view that we have to understand the statistical coarse graining and self-averaging, given observed structure and the limitations of the initial conditions at last scattering when the universe was very smooth.

I do not have an answer to the definition of gravitational energy or gravitational entropy - nobody does - but I believe that progress can be made by returning to the foundations and thinking harder about the equivalence principle, as I have done in my essay and related work. (My hypothesis is that the proper time on your wristwatch, Dimi, is not identical to one one universal cosmic time parameter measured by all isotropic observers, though they are correlated.) A criterion for a physical theory is that one comes up with testable and falsifiable predictions; which I have done. Thus my proposal can certainly be ruled out by future cosmological observations. However, whether this proposal is ultimately successful or not, I believe that the fundamental issues about the nature of time, and ultimately of quantum gravity, can only be addressed by isolating key conceptual holes in our understanding and attempting to address them with quantitative physical models. George asks all the right questions, and his work has inspired me I think more than anyone else's.

Dimi - should you read my work and have any further questions - then since George has closed his discussion, I guess you should continue over at my not-so-active thread. I am afraid I do not have quite as much time and energy as George, but will try to answer any reasonable question.

Merry Christmas to all.

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PS - sorry; thers's a silly typo in my post above; where I wrote

"he identified the key unsolved problems of general relativity as being the definition and nature of gravitational energy..."

should read

"he identified the key unsolved problems of general relativity as being the definition and nature of gravitational entropy..."

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Dear David,

On Dec. 23, 2008 @ 10:22 GMT, you wrote: "My other reason for this post is to address Dimi Chakolov, who has been pestering you quite excessively here."

There is a typo in your sentence. And if you wish to address the arguments and critical comments I posted here, please do it at your thread, and I will respond there.

Please feel free to "pester" me as much as you wish.

I only expect from you to respond professionally to the specific critical comments I made here. George has failed to do it, nor has he responded to any of my email messages sent privately in the past *eight years* (there is no typo here).

Please go ahead, and make your best shot.

Dimi Chakalov

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P.S. Please see my posting at your thread from Dec. 23, 2008 @ 19:32 GMT.

D.C.

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At first Merry Christmas to George Ellis.

I voted for him while I do not share his the idea of an EBU.

At least he did not sacrify time and the "flow" of time for the sake of possibly flawed theories.

To me Christ(mas) and (John McTaggert) Ellis stand for eternalism, presentism, BU, etc.

What I am claiming to have found out is radically different, and it requires to abandon very deeply rooted belief.

Nonetheless my family also enjoys Christmas.

To Dimi Chakalov:

Can you please point me to your own essay. I did not find the name Chakalov in alphabetic order.

Eckard Blumschein

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Dear Dr. Blumschein,

I learned accidentally about FQXi Contest on December 2nd, and was too late to submit my essay. I emailed you about an hour ago, with details about my essay on QM (cf. my first posting from Dec. 2, 2008 @ 07:02 GMT.

Best - D.C.

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George Ellis wrote: "This will be my last posting,..."

The evolving block thread has stopped to evolve. All the postings now exist in an unchanging block thread :)

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RE: the meaning of imaginary numbers & MDT & quantization

Hello George,

I just now saw your post from Dec. 4th, where you write, " George Ellis wrote on Dec. 4, 2008 @ 10:00 GMT

Dear Dr. E (The Real McCoy)

I agree with the spirit of what you do in your essay, which as you point out is going in the same direction as mine. The main point where I differ is in...

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attachments: 2_MDT_PERVADES_NATUREIMAGINARY_NUMBERS_IMPLY_PERPENDICULARITY.pdf, 1_5_MOVING_DIMENSIONS_THEORY_EXAMINES_THE_GRAVITATIONAL_REDSHIFT_SLOWING_OF_CLOCKS.pdf

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I honestly regret that George Ellis choose to leave this Forum. It is still completely unclear to me how one could falsify his hypothesis about "evolving block universe" (EBU), as compared to the hypothesis about some "block universe" (BU).

I was hoping to see some written statement by George, in which he says something like 'if my conjecture [A] turns out to be wrong, then my EBU hypothesis will be indistinguishable from BU hypothesis'.

In this context, perhaps it is worth considering his statement from Dec. 20, 2008 @ 00:42 GMT above, in which he wrote, in response to Lawrence B Crowell:

"there may not be a timlike Killing vector field, but there is a conformal timlike Killing vector."

The issue of 'conformal timelike Killing vector' has not been mentioned in George Ellis' essay. I will refrain from making any comments, and will instead suggest to the Moderator to ask Claus Kiefer to pass his professional comments on two issues:

(i) the applicability of the 'conformal timelike Killing vector' in cosmology, from the perspective of his latest manuscript "Quantum geometrodynamics: whence, whither?", arXiv:0812.0295v1 [gr-qc], and

(ii) George Ellis' claims that "proper time along world lines is indeed a preferred time variable in GR" (Dec. 12, 2008 @ 20:27 GMT) and "objectively privileged hypersurfaces do indeed exist in standard cosmology" (Dec. 15, 2008 @ 05:16 GMT).

D. Chakalov

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Dear Dimitri Chakalov,

Unfortunately, I did not find your email because I suddenly got a huge amount of spam. Maybe I overlooked it. Anyway it would perhaps be better if you made it available to all as an attachment preferably to post in my thread 369 "Let's benefit from special mathematics for elapsed time", provided you do not absolutely deny any relation to what I am considering.

So far I did not at all with the notion BU which sounds to me like possibly unintended mocking about illusions by Dedekind, Cantor, and Hilbert. I rather prefer Galilei's point of view: The relations >, =, < are invalid for infinite quantities.

Just spectral analysis (FT as well as CT) requires all of infinitely much.

Best,

Eckard Blumschein

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Dear Eckard,

I'm also getting a huge amount of spam recently. Please see attached my email address (DC.gif).

George: Please excuse me for this irrelevant, to your EBU hypothesis, note. I hope Claus Kiefer (FQXi Member since 2006) will agree to comment on your ideas, as suggested on Dec. 26, 2008 @ 01:44 GMT.

Dimi Chakalov

attachments: DC.gif

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Dear George Ellis,

In your essay you propose that time flows and spacetime evolves in an irreversible way as the wavefunction collapses. However, you say that this happens pointwise at space-time events, not on spacelike surfaces. This is an apparent contradiction because wavefunction collapse is a non-local process. Can you elaborate on how you reconsile the local vs non-local characterists of the EBU?

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In addition to the issue raised by Philip Gibbs above (Dec. 28, 2008 @ 09:36 GMT), notice that, according to George Ellis, "... a key element is how proper time relates to coordinate time as we move to the future" (George Ellis, Dec. 4, 2008 @ 10:00 GMT). This is a big can of worms, because, according to Carlo Rovelli (gr-qc/0604045 v2, p. 4):

"The proper time [tau] along spacetime trajectories cannot be used as an independent variable either, as [tau] is a complicated non-local function of the gravitational field itself. Therefore, properly speaking, GR does not admit a description as a system evolving in terms of an observable time variable."

Recall Bill Unruh's claim, posted on his academic web site, that there should exist some "explicit (but unmeasureable) time". Twenty years ago, Unruh and Wald suggested that any reasonable quantum theory should contain a parameter, called by them 'Heraclitian time', whose role is to set the conditions for measuring quantum variables and to provide the temporal ordering of such measurements (cf. W.G. Unruh and R.M. Wald, Phys Rev D40 (1989) 2598).

It is not clear to me how George Ellis' EBU hypothesis contributes to these ideas. Since he chose to leave his thread, I suggested to the Moderator (Dec. 26, 2008 @ 01:44 GMT) to ask Claus Kiefer for his professional opinion.

D. Chakalov

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You can relate proper time to co-ordinate time by choosing synchronous co-ordinates, but I they are too problematical for quantum gravity. See wikipedia

http://en.wikipedia.org/wiki/Synchronous_coordinate
s

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Synchronous coordinates are related to the conformal geometry of the universe. If we have g_{ab} --> Q^2g_{-ab} the Minkowsi spacetime scales as ds^2 = -Q^2(dw^2 - dx^2 +...). Then for Q = e^{Lt/6} and dw/dt = Q^{-1} you get the deSitter cosmology which is a case of synchronous coordinates. and ds^2 = -dt^2 + F(t)(dr^2 ...) type of metric has this property, though it is not a case of a coordinate condition.

The frame this hones in on is the Hubble frame, though this is not a case of a gauge choice. Physically we can just imagine that what ever universe there is filled with a hot gas the equilibrium condition will define a Hubble-like frame.

When it comes to quantum gravity we might ponder a number of possibilities. Since the coordinate time t is the time paramter for quantum fields with internal symmetries, and ds is the propertime for gravity, then for supersymmetric (supergravity) theories we might expect that some relationship exists between them which leads to synchroized coordinates in cosmology. Either that or there is some generalization of the whole notion of time.

Lawrence B. Crowell

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I may do it, but I don't want to. This kind of reference system is called synchronous, because "the t coordinate defines proper time for all comoving observers", as stated in Wikipedia at the link above. All this reminds me of the "cosmic equator" (cf. attached), and its discussion by Craig J. Copi et al. in arXiv:astro-ph/0605135v2.

I wonder if George Ellis' EBU hypothesis can explain the alleged "spin" of the observable universe, given his claim that "objectively privileged hypersurfaces do indeed exist in standard cosmology" (Dec. 15, 2008 @ 05:16 GMT).

D. Chakalov

attachments: cosmic_equator.gif

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The WMAP image with the equator I think reflects the presence of the Milky Way galaxy. The photons which come from the galaxy are filtered out and this apparent equator is removed. It is not clear to me there is a preferred direction in the universe, at least based on these data.

Lawrence B. Crowell

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Some while ago I withdrew from the discussion as I had had enough of the bad tempered behaviour on this thread [posting on Dec. 22, 2008 @ 05:42 GM]. A number of technical issues relevant to my paper have however arisen in the subsequent postings, and in order to acknowledge them I will now respond to them in one global response, tackling in sequence the four main themes arising that I see as...

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Correction: instad of dx^a/ds = 1, I meant u^a = dx^a/ds.

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Thank you, George, for your comprehensive reply, in which you wrote (Dec. 29, 2008 @ 17:53 GMT):

"... the surfaces S:{s=const} are the globally preferred surfaces of time (“constant proper time since creation of the universe”) on which coming into being will take place."

I also notice that you define proper time along all world lines in "small local neighbourhoods" on which "coming into being will take place", and I promise that will never ever ask more questions about your research. Good luck.

D. Chakalov

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Dear George Ellis. I am pleased that you responded further to the questions raised. I have another :-)

You defined preferred surfaces s=const where s was determined in a particular way using the curvature tensor and the intial singularty. Is there a proof that these surfaces would be everywhere spacelike for realistic cosmologies with local inhomogenieties? (and if not, does it matter?)

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Dear George Ellis,

As only the BU and EBU do not contradict the relativistic experiments, which involve macroscopic bodies, I have no choice and have to express my disagreement with your conclusion:

"I could go on, but that should suffice to show there is excellent experimental and observational support for the EBU as against the BU."

I think this is not correct on...

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Please add at the end of 2.1 of my post above:

Moreover, it is not unthinkable to imagine that the probabilistic behaviour of quantum objects and the relativistic forever given spacetime picture of the world do not contradict at all (see Section 5 of my essay).

Vesselin Petkov

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Reasoning and faith are two opposites. Just as there is a limit to reasoning so also we have limitations in faith. That is what life is all about. Time sets our birth and death and so the absolute truth or final truth can only be approached but is actually not reachable. Let us all( includes me too)learn to recoincile and be always cheerful even when faced with opposition or violence. Our mental balance and peace of mind are the most treasured, to remain useful towards humanity as a whole.

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Dear Philip Gibbs: your comment is an interesting one. “Is there a proof that these surfaces would be everywhere spacelike for realistic cosmologies with local inhomogeneities? (and if not, does it matter?)” No there is no such proof, and indeed in principal they could become null or timelike; and this probably does not matter. However in the smooth context of a macro description of cosmology, this will not occur. By the way I did not emphasize it, but the choice of world lines I make is that of the Landau reference frame, representing the velocity given by the local average of all energy and mass fields in a small neighbourhood..

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Dear Vesselin Petkov, thank you for another penetrating reply. I will not reply line by line but rather make two overall guiding statements for my view: namely,

(A): Potentialities from the past are realized at the present;

(B) Potentialities for the future are with us at the present.

Everything argument you give as to why one should believe in the Block Universe (BU)...

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Dear Vesselin Petkov, thank you for another penetrating reply. I will not reply line by line but rather make two overall guiding statements for my view: namely,

(A): Potentialities from the past are realized at the present;

(B) Potentialities for the future are with us at the present.

Everything argument you give as to why one should believe in the Block Universe (BU) rather than only 3-dimensional spaces evolving with time, applies also for the Evolving Block Universe (EBU). However, except perhaps for the EPR case which I come to in a minute, according to principle (A), it applies at the present due to the effect of the past at the present: in other words it applies in the 4-dimensional EBU domain which is already in existence. Causality operates as you state it, but only in the EBU region that already exists. This domain is coming into being at the present instant; and what is the present instant now will in another fraction DT of time be in the past. As I believe spacetime is quantised, I am happy to assume DT cannot be taken infinitesimally small but rather has a finite lower limit (associated with the Planck time); so there are no paradoxes associated with the present having zero time extent. I am happy if it has a very small but finite duration. .

You state “On the EBU view, only *one* spacelike surface (which may have a very complex shape) exists and nothing else. In this sense, according to the EBU, the relativity of simultaneity that exists in special relativity is an artifact that does not reflect anything objective.” It represents a construction of what was simultaneous in our past according to our measurements made here and now in the present. This construction (together with the concept of length contraction) helps us understand the 4-dimensional causality that has taken place in the EBY domain that already exists. However of the basic special relativity effects, the only one that is actually physically effective is time dilation, which can be experimentally verified at a single spacetime event. That effect is deeply embodied in the view I am proposing, as it is what underlies the formulae for proper time along a particle world line. What further matters crucially from the 4-d BU spacetime picture is for example the way the electromagnetic field transforms in 4-dimensions; that applies also in the EBU, in the domain that already exists (as a causal effect helping determine the present outcome) and in the potential future (as a way of predicting what will happen if certain future conditions are fulfilled).

You state “Concerning Figure 1 in your essay, the scenario (involving *macroscopic* objects) you describe on p. 3 is perfectly explainable by the BU view - the *existence* of events in spacetime is a *separate* issue independent of whether or not they are unknown and unpredictable at a given earlier event. So the example depicted in Figure 1 is not an argument against the BU.” But in your own essay, you explain “I mean a real four-dimensional world, not substantivalism. In such a world physical objects exist at once at all moments of their histories in time as four-dimensional worldtubes (spatially extended objects) or worldlines (point-like particles)”. They cannot exist at all moments in this way if their outcome is not determined until it happens, as is the case for the 2-slit experiment. The view you put is valid for what I call the Final Block Universe: the state of things that one can contemplate when everything that will ever happen has already happened: the EBY has evolve ditto a final state as a BU and time has ceased to roll on. But it can’t be a good view until then: you can’t depict the way things will be at all times at once, while physical causation is still in progress, if the outcome is not determined until it occurs. I refer again to the 2-slit experiment.

As regards the quantum case, say the double-slit experiment, I have not attempted a description of how particles exist or not in quantum theory. Whatever works for you in the BU words for me in the EBU according to principle (A), except for cases involving entanglement, which I come to in a minute. I hold by the statement that quantum theory only predicts probabilities, not specific outcomes.

Finally, as regards the issue of the EPR-type *experiments*: you state “those experiments are perfectly explained by the BU because the future exists there. But they cannot be explained by the EBU since, on that view, it follows that the non-existing future can determine the outcome of an experiment.” You are referring to

how the EPR experiments relate to Lorentz transformations, and I am not clear on that topic. But at present I think that those experiments do indeed involve a preferred rest frame: the one associated with the average motion of matter involved in the experiment. It is in this frame that the “spooky action at a distance” is “instantaneous”; it will not be instantaneous in any other reference frame. And that fits completely with my picture of the EBU. Insofar as it looks like the future influences the Past in other frames, this will be according to principle (B) above. But as already stated in a previous post, the EPR analysis is not a relativistic analysis: it is based in the Schroedinger equation.

As long as any experiment whatever gives a future outcome that is not at present determined even in principle, the EBU description trumps the BU. And we have plenty of such experiments in quantum theory. The relativistic interpretation of the EPR experiments will have to adjust to this fact.

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Dear Narendra nath, I agree with your sentiments. Its possible realisation depends on an EBU picture being correct, where humans have a hope of influencing the future, because the future outcome is not yet decided. This is what the BU picture denies.

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Thank you all for the interesting and helpful discussions.

I believe you all will agree that we owe special thanks to George Ellis for his amazing care and patience in replying to so many posts.

Best wishes for a happy, healthy, and very successful 2009,

Vesselin Petkov

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Responding to Philip Gibbs, George Ellis wrote (Dec. 31, 2008 @ 05:50 GMT):

[1] "By the way I did not emphasize it, but the choice of world lines I make is that of the Landau reference frame, representing the velocity given by the local average of all energy and mass fields in a small neighbourhood."

Responding to Vesselin Petkov, George Ellis wrote (Dec. 31, 2008 @ 05:52...

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Dimi Chakalov wrote on Dec. 29, 2008 @ 22:05 GMT "I promise that will never ever ask more questions about your research. Good luck."

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Dear Ellis,

Thanks for the comment. i agree that our actions do determine the future, but there continues a major element of uncertainty. it is good that it exists otherwise things will become totally deterministic. i believe that all such dualities are a part of the physical realities of nature. Absolute reality is neither sought in Physics nor it is desired, as one need to confirm everything predicted experimentally and instruments as sensors of Physics will remain limited inspite of technological upgradation. Mathematically also, ther exist limitations as one can never be sure that all variables required in explaining a phenomenon have be given the due weightage and nothing significant has been left out advertently or otherwise.

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In response to the anonymous posting from Jan. 1, 2009 @ 10:31 GMT: I have not posed any questions in my comments from Dec. 31, 2008 @ 14:32 GMT.

I could, for example, ask George Ellis to explain his vision on the non-tensorial gravitational energy in a "fraction DT of time" (cf. Comment #1), but I didn't. The task is known since 1918, if not earlier.

Metaphorically speaking, G. Ellis' EBU hypothesis is like opening the cover of a piano and showing its the moving parts, and then trying to *derive* the actions of the player from the dynamics of these moving parts. Only the player is not there: it is "dark", and we can explain roughly 4 per cent from the composite system 'player + piano'; the rest if a mixture of cold dark matter (CDM) and dynamic dark energy (DDE).

D. Chakalov

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The running of this competition gives a nice example of why the EBU model trumps the BU. In the latter case, what will happen at all times (future and past) is determined by the system dynamics plus initial conditions at any one time. In the case of this competition, the initial conditions set up the system dynamics, including the sztatement "The voting deadline has been extended to January 1, 2009." It is now January 3rd and it is still possible to vote (I just tested it, and cast a public vote successfuly). So what is actually hapening is not the same as what was determined as the stated system dynamics. It is precisely the reality of the existence such unpredictable system responses in the real world (none of us knows when the voting ands commenting will actually be closed down) that makes the EBU a preferable model to the BU.

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George, nice try but it is already predetermined in the BU where the prizes are going no matter how the voting is conducted. I have looked at all the permutations and in fact the BU model predicts that only existing FQXi members will be awarded prizes. LOL o_O.

Happy New Year and many thanks to George for responding in good spirits to so many questions here. I hope that in future contests more of the high profile entrants will find the time to follow his example because it adds a lot of value to the overall project.

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EBU model is preferred over BU and Ellis needs commendation for his exhaustive attention to the largest number of posts. All the very best to everyone. None should worry about the final results as one can only do one's job the best one can. The results should not be in the hands of the doer otherwise people may become workaholics, dangerous if one is not thoughtful enough!

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The fact that the FQXI organizers changed their minds about the last voting date does not proof that this was not pre-determined. Also, in the MWI you would have many branches, so the BU is a collection of different histories.

I think that the EBU is pretty much ruled out by the many theoretical end experimental "no go" results against hidden variables in quantum mechanics. If the EBU picture as proposed in this essay were correct, then the outcome of some past event would be determined after a while, even if you were completely isolated from the rest of the universe. But then that implies the existence of hidden vraibles which point out which terms in the superposition that describes the starte of the rest of the universe are real and which are not before you perform any measurement.

Ellis has argued in this thread that you cannot completely isolate yourself from the rest of the universe. But the arguments presented by Ellis in his essay do not depend on any such arguments.

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I cannot agree with George that his EBU hypothesis could be "a preferable model to the BU" (Jan. 2, 2009 @ 08:13 GMT).

The current BU hypothesis is adopted in basic GR textbooks. Consider, for example, Robert Geroch (General Relativity from A to B, University of Chicago Press, Chicago, 1978):

"There is no dynamics within space-time itself: nothing ever moves therein; nothing happens; nothing changes. [...] In particular, one does not think of particles as "moving through" space-time, or as "following along" their world-lines. Rather, particles are just "in" space-time, once and for all, and the world-line represents, all at once the complete life history of the particle."

LIGO Scientific Collaboration (LSC) have adopted this "block" view, and deeply believe that there is no difference between (i) observing the effects of GW radiation in the *past* (as calculated by Russell Hulse and Joseph Taylor in the case of the pulsar PSR 1913+16), and (ii) the detection of GWs "online", as they tweak the interference pattern at LIGO.

LSC have spend so far hundreds of millions of dollars and euro -- taxpayers' money -- yet all their "runs" have so far produced stunning failures. Yet they are determined to spend even more, perhaps billions, if the three satellites of LISA are indeed launched.

I think this is far more important than the flexibility of choosing the final date for voting. If George Ellis is right, then LSC might have been on a wrong track from the outset.

Perhaps it will be a good idea if George Ellis proves that EBU hypothesis could be "a preferable model to the BU" by calculating the localization of GW energy along the proper time of the wristwatch of LIGO's operator.

Good luck, George.

Dimi

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Hello George,

Above you write, "As long as any experiment whatever gives a future outcome that is not at present determined even in principle, the EBU description trumps the BU. And we have plenty of such experiments in quantum theory. The relativistic interpretation of the EPR experiments will have to adjust to this fact."

Yes! The block universe denies the inherent probabilistic...

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That nothing happens in a spacetime or cosmology is due to the fact that time is a part of the field of gravity. This is what makes time, or at least coordinate time, something which is similar to vector potentials, in particular A_t, with internal gauge symmetries. These things do not exist in a physical sense. Of course gravity is an external symmetry. The gauge, or frame, dependent...

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That nothing happens in a spacetime or cosmology is due to the fact that time is a part of the field of gravity. This is what makes time, or at least coordinate time, something which is similar to vector potentials, in particular A_t, with internal gauge symmetries. These things do not exist in a physical sense. Of course gravity is an external symmetry. The gauge, or frame, dependent quantities in spacetime physics are something we "hang our boots on." This then a motivation for the idea of the block universe. Then quantum mechanics enters the picture and things become troublesome.

The question is whether there is a way to replace the classical block time universe with a quantum block time universe. General relativity does support the notion of there being a single spacetime which is fixed set of geodesics and curvatures. Quantum physics adulterates this view with there being events which correspond to the reduction of states in a measurement or decoherence. Within the Copenhagen interpretation these state reductions are purely random. As a result the block universe is not longer this one set of possible geodesics and curvatures fixed by a single set of mathematical diffeomorphisms. The block universe still remains in some sense from a GR perspective, but where geodesics are connected by points which are determined by wave function collapses that have no causal deterministic principles. Hence we have an uncertain block world. Assume one knows all the Cauchy data on some spatial surface of the world at a time t, where this assumes synchronous coordinates

ds^2 = -dt^2 + g_{ij}dx^idx^j,

such as with FRW and deSitter spacetimes, so coordinate time can be identified with the proper time. This data is then insufficient to determine the state of this world at some later time due to state reductions and the inherent randomness induced by QM, measurement and randomness of decoherence. So as observers moving in the block world we are unable to construct the block from even a complete Cauchy data set we might have available.

So in what way can QM do this? Through the activity of wave function reductions Cauchy data is reduced, or the information it holds at one time is removed from the universe or unavailable at a later time. So the Markovian picture of moving in a block world no longer holds. If we consider this with gravity, this means that there is some physics which is able to adjust Cauchy data, which requires changing the appearance of masses (particles etc), in spacetime that is independent of gravity. Gravitation is a strange field, for it is not like electromagnetism where one can prepare a system in some specific way to communicate an EM wave from one region to another where those preparations can be independent of field data. I can set up an EM wave by introducing acoustical energy into a device or microphone, which is not strictly an EM field process, and use that data to establish an EM wave. To configure masses here and there in GR requires the application of energy which is itself a source of the field. Hence one can't encode new information onto the gravity field which is independent of the prior Cauchy data of the field. Yet, with state reductions it appears that QM in its random way might indeed do just that! The appearance of a particle "here" instead of "there" in a state reduction requires there to be some metric back reaction where the gravity field responds to this randomness. This is the basis for some of the strange physics with black hole radiation.

The block universe might be thought to remain in a pure form with the many worlds interpretation. However the block now includes a vast number of spacetimes which branch out with each wave function reduction. For the QED field the Compton wavelength of an electron is lambda = hbar/mc ~ 10^{-12} cm, and these branchings can occur for every QED process with a fermion on a time t = lambda/c ~ 10^{-22} sec. So for approximately 10^{80} leptons and baryons in the observable universe this could mean that on the synchronous time frame (Hubble frame) the universe branches out in an MWI sense 10^{100} times every second. Then given inflation and our observable universe is just 10^{50}th of the whole thing this indicates the whole universe branches in a huge number of paths every second ~ 10^{150}, and these branches continue and this has been going on since the big bang. I can't say whether this is correct or not, for quantum interpretations appear to be almost undecidable, but this is a lot to swallow.

Rovelli and others appear determined to banish time into dust. This is of course entirely possible. General relativity gives a meaning to proper time, where coordinate time is something determined by a gauge choice. A conformal time, or proper time can lock a choice of coordinate time with proper time, so called syncrhonous time. Yet all one has done is to make an appropriate gauge-like choice so that certain symmetries of the spacetime define a Killing time vector field. As such the notion of a global time is something which is observer dependent and not "real." We could just as well think of this the other way. A geodesic proper time is all that exists, and path integral deviations (quantum fluctuations etc) around that propertime define a local spatial coordinate frame. Then all such possible geodesics define local frames that patch together in a Cech cohomological sense to define a spatial surface. In this case what we call space is now the "fiction!" In that setting the phase imposed (again a gauge-like choice) on the wave functional over all such geodesics (or metric configurations) determines the spatial surface.

It is likely that time, which in a Euclideanized sense is t = hbar/kT is related to temperature. It is due to an averaging over many states or quantum transitions on a fine grained scale. Now, my thesis is that the universe exists at a quantum critical point, where just as with the onset of superconductivity a scale invariance is set in. This means that at the temperature T ---> infinity the physics remains the same, but somewhere below "infinity" what we call time is replaced with something else. That something else is are phase overlaps between unitariy inequivalent quantum groups as defined by nonassociative maps. For two quantum groups G and G' which are not unitarily equivalent, eg there exists no unitary map U:G ---> G', the elements of these groups g and g' are mapped to each other by an associator A:G ---> G', which is nonunitary, by Ag = g' and so a state transition within the group G can overlap with G' by g^{-1}Ag = g^{-1}g'. The associator map A also preserves quantum information! If time disappears something must take its place! These maps are what I think underlie what we call time, and frankly space as well.

In that setting the system of nonassociative maps on a fine grained scale are determined, a sort of block-map world view if you will, and where on a larger scale where time exists there is some ensemble of pos