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RECENT POSTS IN THIS TOPIC

C allen: on 10/27/11 at 13:53pm UTC, wrote Carlo, I was so relieved to read the truth about Time. For a long while I...

C allen: on 10/27/11 at 13:41pm UTC, wrote How refreshing that rovelli proposes that there is no time. To understand...

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FQXi FORUM
August 29, 2014

CATEGORY: The Nature of Time Essay Contest [back]
TOPIC: "Forget time" by Carlo Rovelli [refresh]
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Carlo Rovelli wrote on Aug. 25, 2008 @ 18:36 GMT
Essay Abstract

Following a line of research that I have developed for several years, I argue that the best strategy for understanding quantum gravity is to build a picture of the physical world where the notion of time plays no role at all. I summarize here this point of view, explaining why I think that in a fundamental description of nature we must "forget time", and how this can be done in the classical and in the quantum theory. The idea is to develop a formalism that treats dependent and independent variables on the same footing. In short, I propose to interpret mechanics as a theory of relations between variables, rather than the theory of the evolution of variables in time.

Author Bio

Carlo Rovelli is professor of Physics at the University of Marseille, France and member of the Institut Universitaire de France. His main research interests are in quantum gravity, where he has contributed to the definition and the development of Loop Quantum Gravity. He is particularly interested in the foundations of the physics of space and time. He has written the books: "Quantum Gravity" (2004), "What is Time? What is Space" (2004), and "Anaximander of Miletus" (2008). He has received the 1995 Xanthopoulos Award for his contributions to gravitational and spacetime physics.

Download Essay PDF File




Anonymous wrote on Aug. 26, 2008 @ 10:37 GMT
I truly doubt that thermal time satisfies the properties that we usually expect from time. It might work for thermal equilibria, but what about states out of equilibrium? Especially those which are far out of equilibrium? If one place is hotter than another, does time run at different rates then? More disturbingly, let's say we have a plasma where the electron temperature is much much higher than the ion temperature. It will take quite some time before such a system will equilibriate, and so, it's possible to prepare such a system. Do the electrons experience a different clock rate from the ions then? At the same location? We know that the universe is clumpy; there are voids, superclusters, clusters, galaxies, stars, etc. So, the chemical potential varies from location to location (and so does the temperature). This means that the thermal time evolution has to be mixed with an approximately conserved baryon and lepton number symmetry which is "gauged" in the sense that it varies from point to point.

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Anonymous wrote on Aug. 26, 2008 @ 10:49 GMT
There's another huge problem with thermal time in a timeless universe with a thermodynamic arrow of time. If we choose to describe the ensemble at an earlier time, that would be different from describing the ensemble at a later time (based only upon the macroscopic degrees of freedom) because information is lost into microscopic correlations irreversibly. Which ensemble should we then use in a timeless universe? But if you say the earliest possible ensemble, then the flow of time would be way out of whack at "later times".

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Anonymous wrote on Aug. 27, 2008 @ 11:40 GMT
I think thermal time conflicts with the philosophy that time is what is measured by the correlation of partial observables with clock pointers. In a thermal equilibrium, clocks simply can't exist!

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Ming wrote on Aug. 29, 2008 @ 08:18 GMT
It seems to me that in terms of logical priority/primitivity, Quantum Theory (QT) should precede General Relativity (GR) as the more fundamental theory of Nature. Thus I believe we should take seriously what QT is telling us about Time and its peculiarities and try to derive GR as a macro approximation instead of doing it the other way round like the author is suggesting.

The Wheeler-DeWitt equation, upon which Rovelli's arguments (and very similar ones by e.g. J. Barbour) are based, is of questionable validity in reality due to the fact that we do not yet have any consistent theory of Quantum Gravity. Thus the "Timeless" world views inferred from it are of questionable validity as well, even if we don't consider the fact that these world views cannot be further from our physical intuitions...

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Anonymous wrote on Aug. 29, 2008 @ 10:49 GMT
I take back my comments about the ambiguity in choosing the ensemble when there's a thermodynamic arrow of time. It shows that I still haven't gotten the central concept of timelessness, namely that the only instant which exists is "now", and that statements like the future or past state of a given state make no sense in a timeless universe. Timelessness is a theory of instants.

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C allen replied on Oct. 27, 2011 @ 13:41 GMT
How refreshing that rovelli proposes that there is no time. To understand this you have to imagine yourself in a universe with no matter - all is still and silent and dark. Then you see a planet and lo and behold suddenly there is movement -rotation etc. Only then when we measure it's evolution and it's becoming, only then do we employ ' time' as measurement. So there is only evolution and velocity.

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Anonymous wrote on Sep. 1, 2008 @ 16:12 GMT
"At the same time, the entry should differ substantially from any previously published piece by the author."

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Alex Nelson wrote on Sep. 7, 2008 @ 04:16 GMT
"If one place is hotter than another, does time run at different rates then?"

Yeah it would logically since the energy at that point would be greater, so spacetime would be "more curved" (according to classical general relativity) which results in time "running faster"...so there's a sort of "limit" to what we already know right there! It'd be interesting to relate this to the relativistic red shift, and so on.

Actually, this quoted criticism is a sign of a good theory of time in itself in my opinion.

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Alex Nelson wrote on Sep. 7, 2008 @ 04:50 GMT
Ming wrote: "The Wheeler-DeWitt equation, upon which Rovelli's arguments (and very similar ones by e.g. J. Barbour) are based, is of questionable validity in reality due to the fact that we do not yet have any consistent theory of Quantum Gravity."

Unless I am misinterpreting Dr Rovelli's paper, I think that he is calling the Hamiltonian constraint in general the "Wheeler-DeWitt equation" (as opposed to referring to the infamous one in the ADM forumalation of canonical general relativity).

In section V, where he discusses the "Wheeler DeWitt equation", it is merely some Hamiltonian constraint and nothing more. This is a constraint which always appears for relativistic systems, it seems to show up with relativistic particles and forces.

That's just my two cents though...

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Dr. E wrote on Sep. 29, 2008 @ 21:08 GMT
Hello Carlo,

Thank you very much for the paper, which I enjoyed.

However, instead of forgetting time, perhaps we should forget quantum gravity for a moment? For while time manifests itself throughout classical, relativistic, and quantum mechanical physics and our empirical reality, the graviton has never been seen.

Do we have to quantize gravity? Could it be that nature is...

view entire post


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Quantum Gravity is a Multi-Million Dollar Hoax wrote on Oct. 11, 2008 @ 04:09 GMT
Do a search at NSF on "time quantum gravity."

http://nsf.gov/awardsearch/piSearch.do;jsessionid=7
F7E1A09E64B392775A7855BA8211E51?SearchType=piSearch&page=1&Q
ueryText=time+quantum+gravity&PIFirstName=&PILastName=&PIIns
titution=&PIState=&PIZip=&PICountry=&Search=Search#results

Yo
u will see that using quantum gravity to understand time is nothing new.

The research has received millions upon millions of dollars, and yet has produced abosolutely nothing but for aging quantum gravity regimes. NSF is just the tip of the iceberg.

All these millions upon millions, and yet, there is no:

1) graviton

2) consistent theory of quantum gravity, nor anything even close

3) any reason to go on

And yet, as the purpose of fqxi is generally to

1) fund well-funded, institutionalized crackpottery &

2) recreate physics in old physicists' image,

I imagine any essay that mentions time and quantum gravity will receive an award or two from the ruling pseudo-physicists.

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Brian Beverly wrote on Oct. 11, 2008 @ 05:57 GMT
Quantum Gravity Conspiracy Theorist,

Your poorly copied URL link returns the following:

“Nothing found to display.”

I doubt this is your fault; instead these multi-millionaire physicists deleted all records to throw us off their trail. Congratulations you’ve earned a scooby-snack for all of your detective work. It is a shame that earlier generations fell for the “ether” hoax and wasted all that money on the Michelson-Morley experiment. Everyone should write their congressmen and tell them not to support null experiments before we spend any money on them.

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Carlo Rovelli wrote on Oct. 13, 2008 @ 12:48 GMT
I try to reply to the various posts.

A certain number of posts raise a question that in my opinion is a very good and a very important question. The question, that some of the post present as a strong objection, is that the hypothesis of thermal time is not good, because it only deals with thermal equilibrium, while we need non-equilibrium states to have non-trivial time phenomena. I...

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John Merryman wrote on Oct. 14, 2008 @ 02:20 GMT
Dr. Rovelli,

I would agree time is a measure of motion, similar to temperature, but that doesn't clarify how the effect emerges. Temperature is like a parallel processor, with lots of activity and interacting elements. Time is a serial processor, with the point of reference/observer/hand of the clock proceeding though a series of intervals/events. Observer and observed co-exist, as all elements in the thermal medium co-exist, so there is no dimensional projection out from this state. As a serial processor consists of innumerable serial processors, innumerable clocks exist in a thermal medium, as every point of reference moving in this thermal state constitutes the hand of its own clock, while all other points are face to that clock and hand of their own clock. So while all these points move from past events to future ones, the events, once created, are replaced by the next and so go from being future potential to past circumstance. Just as tomorrow becomes yesterday.

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John Merryman wrote on Oct. 14, 2008 @ 02:24 GMT
Correction: fifth sentence; As a parallel processor consists of innumerable serial processors....

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nnath wrote on Oct. 15, 2008 @ 00:42 GMT
This essay contest is wonderfully explaining how individuals have widely varying interpretations for a given phenomenon. This is parallel to a common man's observation when he listens to different eyewitnesses who happen to see the same event but their their descriptions vary substantially. Absolute truth appears a mysterious quantity and science can only describe relative truths about a process/phenomenon that change with time. There lies the mystery about time too.

Yoga is a technique to quieten the mind. It was evolved by a saint in India thousands of years back. That scripture has two relevant quotes about the search for truth. One states ' The cognizor, the process of cognition and the object of cognition must all merge in order to find the truth about the latter. Another states' there are mental distractions like ego or I-ness, ignorance, pleasure and pain which prevent the human thought processes from reaching the highest level required to get to the truth.Thus, without extreme humility and contemplation in 'silence', it is well-nigh impossible to know the 'truth'.

This comment is posted here but is too general to be applicable to all the contributors including the self!

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Carlo Rovelli wrote on Oct. 15, 2008 @ 07:58 GMT
John Merryman's post says:

"I would agree time is a measure of motion, similar to temperature, but that doesn't clarify how the effect emerges." and then observes that temperature does not have the sequencial aspects that characterize time.

I thinnk that there is something vey interesting in this post, when it says "doesn't clarify how the effect emerges". My reply: "which effect?" What is the "effect" we are talking about here, and trying to understand?

The central point about all my ideas about time is to distinguish two different "effects". One is the observed fact that there are laws of nature that fix how variables are correlated. My claim is that this perfectly captured by our dynamical theory, but these theories do not truly distinguish "time varables" or "clock variables", from the other variables. This is effect one and point one.

But this is a bit unsatisfactory, because we have an idea of time as something "flowing", something very peculiar, very different from other variables. This peculiarity, this flowing, is effect two. So, the "effect" that remains to be understood is the peculiar impression we have about the flowing of time. The thermal time hypothesis states that this effect two is of thermodynamical origin. This is not my idea: it has long been remarked that all our impressions of "flowing" time are related to thermodynamics: only in a thermodynamical situation we may have irreversibility, for instance, and we may have memory. Eddintong has remarked that a periodic clock is not truly a clock unless we can count the cycles, namely unless we break periodicity. And we introduce some sort of irreversibility. Eddington noticed that the true prototype of a clock is not a pendulum: it is a burning candle (we ourselves are burning candles). A burning candle is a thermodynamical phenomenon. Going towards the future is mouving towards thermodynamical equilibrium.

So, summarizing: all temporal "effects" that are captured by ordinary mechanics have nothing to do with thermal time. They just have to do with the fact that there are laws that govern the relations among variables. The additional peculiar "flowing" of time is an "effect" which is not the same thing as temperature, but (if we believe the thermal time hypothesis) it emerges in a thermodynamca;/statistical situation only.

Carlo Rovelli

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John Merryman wrote on Oct. 15, 2008 @ 16:10 GMT
Dr. Rovelli,

My point is that time and temperature are both descriptions of motion. Temperature is the level of activity against a given scale. Time is the rate of change relative to a given reference frame, or point. If you change the level of activity, you affect the rate of change. The candle burns faster if it is hotter. As a person in space ages slower than a person in a stronger and more active gravity field. So there is the element of time in temperature and the element of temperature in time.

Time has this sense of "flowing" because we exist as individual points of reference in a larger context, just as individual atoms of water move about in their fluid context, the whole of which is measured as temperature. Just as economic statistics function as a temperature reading of masses of human activity. So to the extent we "move" or "flow" within our medium, it moves the opposite direction. To the hands of the clock, the face moves counterclockwise. This manifests in the larger scale by the events which all these points of reference collectively create go from being in the future to being in the past, as each is replaced by the next, while those references go on to future events. Tomorrow becomes yesterday.

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John Merryman wrote on Oct. 15, 2008 @ 16:33 GMT
Molecules of water.

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Narendra Nath wrote on Oct. 16, 2008 @ 14:17 GMT
Dr. Rivoli,

Your idea to discard time as a variable appears fine. However, the concept of time appears hard to discard. It seems to me that the quantum conjugation of time with energy provides a possible way out of the problem of time. Initial distortions of time may have resulted in the release of the energy content of the Universe. Similarly, the space distortions provide the momentum, a combination of mass with motion. Without any motion or vibrations, the Universe will become meaningless. Pure, vibration free consciousness can not give rise to either mass or energy.

Conceptually, it may be possible to replace the time with some other physical quantity and still retain the physical explanations for various observed phenomena. you have proposed some kind of thermodynamical variable to replace time. However, i am unable to comprehend the basis and depth of your argument. I am an experimentalist among most of the essay authors who are theory experts! However, science is neither theory or pure experiment. It starts with some precepts based on observation and experience of the scientist. These are then translated into some viable logical concepts. After this gets done come the question of choosing the variables. The nature of variables again depends on what we take as dependent or independent entity. There can be a subjective element here. As Einstein often expressed that in spite of proposing the quanta of energy, he was unhappy with the quantum mechanical explanations of the phenomena that is entirely probabilistic in nature.

The nature can not be purely governed on such a consideration as it exhibits order, logic and symmetries, besides elements of random nature o/c impossibility of measurement on single event to study a process! Thus, the need for measurement requires averaging over several independent events. Order contains disorder but not vice- versa. Also, silence contains noise but not vice-versa. How to work out this dilemma, appears to be challenging in order to work out a single theory to explain everything!

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Peter Morgan wrote on Oct. 16, 2008 @ 17:48 GMT
Dear Prof. Rovelli,

Your invocation of Tomita flow requires that the algebra of operators be, as you say, a von Neumann algebra, as well as requiring a state over the algebra. A von Neumann algebra has a Norm, by definition, which, I claim, must have a *timeless* meaning for your argument to go through.

The Norm of an algebra of observables decides what measurements are close to each other -- that is, the topology -- which allows us, by continuity, to decide whether we expect, in a given state, that the results of one measurement will be close to the results of another experiment. We can only verify that two given experimental procedures are close to each other by applying them to many different states, thereby determining that we get almost the same results (according to some Norm on the space of results) in every state. Given the statistical nature of a state -- as much in classical statistical mechanics as in quantum theory -- this requires us to construct many ensembles. Now, how are we to construct these multiple ensembles timelessly?

As an ideal world, of course, you are quite entitled to posit any mathematical structure you like, but I would like to see a Physical interpretation include at least a schematic for an operational correspondence with the world for every significant mathematical structure. In any case, given its significance to your account of time, I would like to see a relatively full account of how to understand the Norm of the von Neumann algebra in a timeless way, whether operational or not.

I apologize if this question is well understood. I don't follow the literature on quantum gravity closely at present. Please feel free just to cite a reference.

I'm perhaps simply at cross-purposes with you, since in the last sentence of section VI you assert that the world is "in" a given state rho, which suggests that you understand QFT in terms of a non-ensemble interpretation of probability. However, I would personally take a non-operational definition of probability also to be problematic for your program.

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Eleni wrote on Oct. 17, 2008 @ 23:45 GMT
Thank you very much for the essay. I enjoyed reading it, I expect you will expand it more.

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T.H. Ray wrote on Oct. 18, 2008 @ 12:34 GMT
Carlo Rovelli's statement, "Research needs courage, wasted time and money, false directions. The history of our civilization is the proof that all this money is not wasted, in my opinion..." is a point well made.

Nature shows in all ways that waste and redundancy are assets to creativity. Efficient evolution is guaranteed by conservation laws, and not by the efficiency that we vainly try to build into a system.

Tom

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John Merryman wrote on Oct. 18, 2008 @ 17:32 GMT
No chaff. No wheat.

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Carlo Rovelli wrote on Oct. 19, 2008 @ 08:15 GMT
Thanks Eleni, Ray and John for the last nice posts.

Peter Morgan raises an extremely good issue, with both a technical and a conceptual side. I refer here to his post above, without trying to repeat here his points, since these are several, interconnected, and nicely expressed by Peter.

First, a technical point. It is true that Tomita theory wants a von Neumann algebra, and...

view entire post


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F. Le Rouge wrote on Oct. 19, 2008 @ 16:53 GMT
The way Dr Carlo Rovelli is questioning Time is may be new in 'Quanta Theory' but not in Antique Greek Metaphysics that does analyses the connection of Time with Space in Motion precisely. This is the case of 'Eleates' (6th bc - although Eleates deduce there is no motion at all!) and Eleates are not lonely.

No doubt that the analogy between the dynamism of Time and the dynamism of Heat is one of many comparisons that are leading to new 'kinesis'. One can find that in Boltzmann's science of gas pressure for instance. Therefore the 'Question of Heat' is as 'mysterious' as the 'Question of Time'.

Such a link between Heat and Time is established by some Antique Greek scientists too.

So the good question is not in my opinion if the Antique Greek Metaphysics is up to date or not; Dr C. Rovelli's essays are just proving it is still alive.

The right question is: do Greek old masters go beyond in time analysis than actual physicians? The goal is not to rise up old Methaphysics against modern Science but to know if the Greek Metaphysics can impulse a better logic to a technological Science that seem to be possessed by doubt in the field of logic.



(I am student in an Art-School and making an writing an essay about Geometry and Newton's chromometric scale. My interest goes to the problem of Time too. Even if I am not focused on number four and 'Quanta theory' which recalls the famous trial consisting in squaring the space of the circle, I intend to publish a chapter of my own iconoclastic artistic vision in a few days on www.fqxi.org).

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John Merryman wrote on Oct. 19, 2008 @ 21:38 GMT
Dr. Rovelli,

I agree that the issue of consciousness distracts from the question of time. I think both time and temperature are elemental to motion. That said, our mental facilities are a consequence of feedback between the source of this consciousness and motion. E.O Wilson described the insect brain as a thermostat, while the neuroscientist J. B. Taylor provides interesting insights between the 'serial processor' of the left hemisphere of the brain and 'parallel processor' of the right hemisphere;

http://blog.ted.com/2008/03/jill_bolte_tayl.php#m
ore

I would argue that the right brained parallel processor amounts to a thermostat, in its measuring and reacting to the energies of the moment, while the left brained serial processor amounts to a clock, in that it analyses the sequential cause and effect of events.

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John Merryman wrote on Oct. 19, 2008 @ 21:45 GMT
In traditional lore, this dichotomy was between the head and the 'heart.'

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F. Le Rouge wrote on Oct. 19, 2008 @ 21:47 GMT
*Another analogy: keeping as separated as possible the physics and the science about cognitive capacities is probably as difficult as for the Greek scientists keeping physics and metaphysics separated.

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Narendra Nath wrote on Oct. 20, 2008 @ 15:03 GMT
Does Dr. Rivolli think my posting unworthy of a response! i am however curious to know why he consider it to be so, just because it doesn't involve detailed discussion on the mathematical treatment used or the points raised are irrelevant!

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Anonymous wrote on Oct. 20, 2008 @ 21:28 GMT
This is more like a paper than an essay. It also seems to be way over 5000 words.

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Carlo Rovelli wrote on Oct. 21, 2008 @ 16:47 GMT
Dear Narendra Nath, I am sorry, I did not think that your post unworthy of a response! I just did not know what to answer. Your suggestion that "distortions of time may have resulted in the release of the energy content of the Universe" is interesting, but I think is still to vague to be useful is physics. (By the way, my name is Rovelli, not Rivolli. But "Rivolli" sounds nice and funny to me... I might adopt it!)

Regarding the anonymous post "This is more like a paper than an essay. It also seems to be way over 5000 words.", I am also not sure what to say. Is this somebody interested in a scientific discussion or a contest competitor? :-) Anyway, the text alone without math gave less than 5000 words on my word counter. And I think the essay is an essay, not a "paper", whatever this means. It uses some technicalities, because I think they make the point concrete, but the main point is entirely a conceptual view about time, its absence, and its emergence.

Carlo Rovelli, (or Rivolli)

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narendra nath wrote on Oct. 22, 2008 @ 10:24 GMT
Rovelli or Rivolli,

i enjoyed your pun, my mistake arose o/c the name of a cinema hall i use to visit in New Delhi to see western movies!

I have posted a latest one on the essay of Kyle Miller 'here and now'. That post is actually meant for we all the essays' authors. Kindly see it and then you and i will have no problem if you and i understand or not anything that any one else is saying or writing!!

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F. Le Rouge wrote on Oct. 22, 2008 @ 11:07 GMT
Biology is crossing Physics in motion, either you take the Dynamics of Time or the temperature's one.

And both 'Quanta theory' - think of the motion of gas depending from temperature - and Relativity are based on reflexions on the arrow of Time AND the pillar of Temperature.

Light is the 'check point' of 'Quanta theory', Einstein's theories, without forgetting Newton. And the idea of Temperature and the idea of Time are included in ambiguous light.

This is the knot. And in my artist opinion, 'pulling the time over', Dr Rovelli is cutting the knot as Alexandre did (Although Aristotle was Alexandre's advisor and not Anaximander of Miletus).

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Narendra Nath wrote on Oct. 22, 2008 @ 13:51 GMT
About your comment on energy coming from distortion in time, it is already covered under Heisenburg uncertainty relations, between two conjugate pairs E & T and X & P. Both energy and mass get created as uncertainty rise in time & momentum respectively. The former provides the classical way to explain overcoming of potential barrier the alpha particle experiences inside the unstable nuclei concerned.Near zero uncertainty in time means infinite energy uncertainty!Time may have begun this way!

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Peter Lynds wrote on Oct. 22, 2008 @ 16:15 GMT
Dear Carlo,

I very much enjoyed your essay. Naturally, I very much agree with its general drive too. I have a question though. As a proponent (and founder) of Loop Quantum Gravity, are you not assuming the existence of time by asserting that time (and space) are quantized, and come as minimum, indivisible atoms in LQG? I think one can see this just in general, but also that by asserting the existence of indivisible, minimum time and space intervals, one is also assuming the existence of instants in time and spatial points (things that would constitute the building blocks of time and space and which certainly do not exist) to bound and determine such intervals. I naturally have no problem with Planck time and distance - intervals beyond which clocks and rulers can no longer have meaning – but this does not mean that continuity ceases beyond this point, not does Planck time and distance require the existence of instants and spatial points.

Best wishes

Peter

PS: I should note that, considering its emphasis on background independence and its adherence to 4-d, I find LQG the most promising current approach to quantum gravity. It is just the "atoms of time and space" that I have a real problem with. I'm not sure if LQG could be reformulated without this feature and still be "LQG" however.

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Carlo Rovelli wrote on Oct. 24, 2008 @ 17:53 GMT
Dear Peter,

thanks for rising this key point. You say: "Are you not assuming the existence of time by asserting that time (and space) are quantized, and come as minimum, indivisible atoms in Loop Quantum Gravity"? Very good point. Here is what I think:

Einstein great discovery, of course, is that the two things are in fact the same. The two things are: on the one hand, the...

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Peter Lynds wrote on Oct. 24, 2008 @ 21:46 GMT
Dear Carlo,

Thanks. I thought that was an excellent response. I agree with everything you said as well. It's also nice as, with your interpretation of time and space in LQG, we both get to come away happy; no time, no space, no quantizaion of "time" or "space" etc. If only physics worked out this way all the time!

Best wishes

Peter

PS: I use that Einstein quote in my essay. It is remarkable how this point has been lost on so many.

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John Merryman wrote on Oct. 25, 2008 @ 10:32 GMT
Dr. Rovelli,

One question with regards to space; Is this gravitational field ultimately a singular entity, as in Big Bang theory, or is it ultimately distributed, as in a fluctuating vacuum?

Given you describe it as "flat," I assume you think it is distributed.

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Narendra Nath wrote on Oct. 26, 2008 @ 06:21 GMT
Drs. Rovelli, Merryman and other postings from public,

my comments here will concern the theme 'TIME'.Giving a meaning to life introduces time as a concept. It is at the root of life. Timelessness means that there is total freedom and complete randomness around. The latter is the scenario for all the physical processes/phenomena, as these have been understood only on probabilistic considerations. No individual event can be pre-detemined in time!

Now let us see what space is. If no location is desired, we have the spaceless situation. Only if one exists, it is enough for it to know it exists, no need for location. However, if two or more exist simultaneously, there is need for location in space. If we all agree to say that we are one then where is the need to assign different locations.

In psychology/logic, we deal with just 0 & 1 as the numbers. In fact, all other so-called digit numbers are obtainable through some manipulation of only these two digit numbers.The existence and non-existence can thus be treated as two sides of the same coin, both equally significant or insignificant. Such is the problem before us o/c the duality nature of all worldly things/matters.

An interesting combination of two set of terms and traits may be provide us with some humor! Let us take a set of service, love, knowledge and life. Then, let us take another set of attitude. reason, intellect and time. If we combine the corresponding terms and traits with words 'with' and then 'without' in turn, the net result comes out to be selfish,false,ego and finite in the first option. The other option provides us with selfless, true, ego-free and eternal. The latter is a desired ( theoretical) set of objectives while the former results in a factual( practical) situation.

Hope i have posted something down to earth with regard to TIME and its sister SPACE!!!

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T H Ray wrote on Oct. 26, 2008 @ 09:29 GMT
I appreciate your careful distinction in previous works between partial observables (results of events in measure theory) and complete observables (number predicted by a mathematically complete theory).

Insofar as mathematically complete classical theories, such as special and general relativity, are time-dependent (even if time is only a theoretically useful fiction), it seems that indeed...

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F. Le Rouge wrote on Oct. 26, 2008 @ 14:34 GMT
Let's forget the Time, then the Space, and why not the Matter after all? Let's move into a cadastral survey instead of real houses if the quantities and the variables are preceding the things and the matter and not deduced from them. That would be an original solution to housing crisis.

One can notice that, starting from the same mixing of Time and Space variables (which is not what Newton and Einstein are doing), Superstring theoricians are making n-levels buildings.

In my opinion, Rovelli's theory and Superstring's one are both 'interstitial' sciences. Translated in Aesthetics I would say they are 'musical'.

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Dr. E (The Real McCoy) wrote on Oct. 27, 2008 @ 14:20 GMT
Hello Carlo,

Thanks for all the detailed responses above.

You write, "The "atoms of space" and the "atoms of time" of LQG are only figures of language, to indicate that certain physical observables aspects of the gravitational field have a discrete spectrum."

As gravity has never been quantized, and as gravitons have never been seen, and as neither time nor space has been quantized, and as "atoms of space" and "atoms of time" have never been seen in the lab nor universe, and as there is no consistent, finite, accepted theory that predicts atoms of space and time, I think it is erroneous to conclude that "certain physical observables aspects of the gravitational field have a discrete spectrum."



Perhaps I am misundertanding what you mean, but what are the "physically observable aspects" of the gravitional field which have a discrete, quantized spectrum?

Thanks Carlo!

Best,

Dr. E (The Real McCoy)

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Peter Lynds wrote on Oct. 27, 2008 @ 17:40 GMT
Dear Dr. E,

I think he is referring to the "readings" of clocks and meters. Although these are observable, I should note that I disagree with Carlo that clocks and rulers measure anything. As they do not refer to anything except themselves, they themselves "represent" intervals of time and space. I think it is very reasonable to argue that the gravitational field is quantized, while the constitutes of clocks and rulers certainly are quantized. From this, one must operationally conclude that readings of cocks and rulers are quantized too. I think the crucial (and somewhat subtle) point, however, is that all one is essentially saying here is that matter is quantized - not that "intervals" of time and space are. Again, there is nothing "there" to be quantized. The problem obviously pops up when people then start talking about "time" and "space" actually being quantized, the existence of atoms of time and space, Chronons etc. This also means that, although Planck time and length represent an operational roadblock for clocks and rulers, there is no reason why continuity shouldn't be possible on possible smaller scales.

Best wishes

Peter

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Dr. E (The Real McCoy) wrote on Oct. 27, 2008 @ 19:38 GMT
Hello Peter--'tis an honor to hear from you! I have been a fan ever since I read your paper on Zeno's paradox a few years back on slashdot. I reference your work in a longer treatment of Moving Dimensions Theory.

Yes--you write, and I agree, that "Although these are observable, I should note that I disagree with Carlo that clocks and rulers measure anything. As they do not refer to anything except themselves, they themselves "represent" intervals of time and space."

I think you will greatly enjoy the attached informal treatment of clocks and rulers given by Moving Dimensions Theory, which accounts for the gravitational redshift and the gravitational slowing of clocks, while also showing that there is no need to quantize gravity. Space is seen as continuous, and quantum phenomena (wave-particle duality/nonlocality/probability) is seen to descend from the fundamental wavelength of the fourth dimension's expansion, from which relativity is derived in my paper. dx4/dt = ic, and the wavelength of this expansion is Planck's length. And every timeless, ageless photon, which remains stationary in the fourth expanding dimension, agrees! It also deals with Planck's length in a novel, sensical manner.

The tautological definitions of time and the velocity of light, rest upon MDT’s fundamental invariant of dx4/dt=ic, which ensures that c is always measured to be c, even though the rate of time changes close to gravitational masses. MDT’s invariance underlies Einstein’s observation, “My solution was really for the very concept of time, that is, that time is not absolutely defined but there is an inseparable connection between time and the signal [light] velocity.”

Thanks for the words! Enjoy the attached brief paper--an updated version of what I posted on my own topic earlier today.

attachments: MOVING_DIMENSIONS_THEORY_EXAMINES_THE_GRAVITATIONAL_REDSHIFT_MCGUCKEN.pdf

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Narendra Nath wrote on Oct. 28, 2008 @ 02:23 GMT
Dear Carlo, you have the distinction of having the highest postings thus far. It is fine as the essay is invoking wide response. However, may be, don't we all need to broaden our overall outlook on the subject, rather than sing our individual 'songs'. The truth is never confined to an individual. It encompasses us all and unites us with the creation itself! i still await your specific comments on the posting made on Oct 26. it appears naive in nature but we need to contemplate deeper, beyond our individual scientific achievements may be!

In a strange layman's way, i hint at dispensing with both space & time but not 'gravity' as a concept! i also seem to have reservations about Quantum Mechanics, in a small way similar to what Einstein himself opined at its possibly better alternative to emerge one day!!

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Clinton "Kyle" Miller wrote on Oct. 28, 2008 @ 21:01 GMT
Dear all,

I wanted to make some comments about this "essay" along with the comments I have seen above.

I wanted to point out the comment made by Narendra (which has seeminly gone unnoticed):

"An interesting combination of two set of terms and traits may be provide us with some humor! Let us take a set of service, love, knowledge and life. Then, let us take another set of...

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John Merryman wrote on Oct. 29, 2008 @ 02:30 GMT
Kyle,

The knowledge of our being recedes into the past, but it propels the essence of our being into the future.

Without knowledge there is no past. With no past, there is no future.

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Narendra Nath wrote on Oct. 29, 2008 @ 02:58 GMT
Dear Kyle and Carlo,

Our essay discussions are joining the voices of young 20 yrs with elders over 75 yrs. The wide spectrum provides the wealth hidden in our deliberations. We all need to assimilate the differing points of view and then comprehend them as mere complementary to one another. Thus, humanity gets enlightened.

If we try to work a bit harder and concise our presentations in discussions, the impact will be greater. Details are mere words that are used to expand the basic points of view!

i still await the response of our learned author, Carlo to the postings made on 26 and 28 Oct. by me!

As 'consciousness' is being used and invoked quite often in our discussions, i will attempt to add a few points:-

1. Actions take place through consciousness while our thoughts are with or without the same.

2. Energy for It comes from knowledge

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Narendra nath wrote on Oct. 29, 2008 @ 03:21 GMT
unfortunately, my posting got on the site, without my completion, sorry for interruption!!

2. Energy comes from knowledge and enhancement comes from the 'wisdom' component.

3. Motivations lie in self will and desires. However, one needs to be careful to maintain smooth coordination between wisdom, will & desires, as these traits build ego too. It is

good to temper acts with a spirit of continuity, giving and observing the apparent opposites with calmness and reconciliation.

4.Waking, dreaming and sleep are the three known states, to which 'meditation' may be added. It is a state where we know 'we exist' but we become unaware of 'where we are'.This help provides freshness, sensitivity and all-encompassing beauty to the train of thoughts within. One is awake restfully!

5.Each body cell has life-force independently. Normally, a person has many cells in decay mode or even dead. Meditation helps individual cells to get strengthen and provide 'bubbly' enthusiasm in our actions.

6. Power of observation, differentiating discrimination and clarity gets enhanced.

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Dr. E (The Real McCoy) wrote on Oct. 29, 2008 @ 20:15 GMT
Thanks for the rockin' words Kyle!

You write, "However, I want to make it clear that science is my greatest passion. Yet I see science today as an faint glimmer of what it could be. We lack the heroic attitude as Dr. E has made quite evident in his postings and essay. We also have 'sold' nature short--instead of letting children witness the awe and wonder of the cosmos, we placate them with...

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Narendra nath wrote on Oct. 30, 2008 @ 05:23 GMT
Real McCoy (Dr.E), Kyle & Carlo Rovelli, the author,

i am getting confused with author's wise silence while Dr. E continues with his lengthy comments. The young Kyle put in some freshness as expected from the young but most of us continue to sing about ourselves. May we all join to bring cohesion, preciseness to our large number of postings on this essay. i firmly believe science can only talk about relative truths and none of us need bother philosophically to project the ultimate truth. Theories have names tied just as each of us have a tie with a name. Neither seem to hold for long. Only when one has the capacity to broaden to the level of cosmos and then comprehend the phenomenon being attempted for explanation,the right direction is likely to be missed!

IT IS TIME CARLO COMES UP WITH RESPONDING POST and clear the mess from building up!

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Paul N. Butler wrote on Oct. 30, 2008 @ 08:37 GMT
Carlo and all previous responders;

I find it amazing how one can dance completely around a point without seeing it, but we are all somewhat subject to that problem so I can’t say too much. First many picked up that time seems to be connected to motion, which is true. It is also interesting that you desire to replace time with thermodynamics, which can generally be considered to be a...

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John Merryman wrote on Oct. 30, 2008 @ 11:00 GMT
Paul,

"Time then is not a separate entity that somehow flows in one direction, but the measurement of motions through distances. It is the motions themselves that give us the sense of flow as they flow all around us. When you understand that it is the continuum of motions that are flowing, it is easy to see why they only go in one direction because a motion goes in one direction until it is acted upon by another motion and then it may go in a different direction or at a different motion amplitude as a result of the interaction. This pattern of motions and interactions between motions is continually happening all around us. The only way to go back in time (or at least appear to do so) would be to simultaneously reverse all motions in the universe and then reverse them again when they were back to the positions that they were in at the previous condition of all motions that you wanted to get back to. "

So time and temperature are emergent descriptions of motion.

As such, it seems the real confusion over time is that by modeling it as a fundamental dimension, the tendency is to view it as going from past to future. While Einstein disproved it is a fundamental dimension, he still seemed to model it as going from past to future, yet as an effect of motion, where each event is replaced by the next, what we view as this linear dimension of cause and effect is actually going the other way, from future potential to past circumstance.

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Narendra nath wrote on Nov. 1, 2008 @ 13:57 GMT
Many comments have come during the past week and Carlo Rovelli is keeping a wise silence among some lengthy narrations. Let us make him feel easy to respond to what he feels like responding. The next post may be reserved for the author to clear the 'mess' getting generated on such a nice essay that attempts to simplify rather than complicate matters in understanding what Nature has done for us by creating the Universe, then our Earth and then trees/plants, animals and finally we humans with ability to comprehend it all!

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Paul N. Butler wrote on Nov. 2, 2008 @ 06:25 GMT
John;

You are exactly right. Temperature is the measurement of the average free motion in an isolated system containing a large number of energy photons and, or matter particles and since these motions all have motion amplitudes and travel through distances they exhibit the property of time. It is just a more average statistical time structure than if you could look at each individual...

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John Merryman wrote on Nov. 2, 2008 @ 15:32 GMT
Paul,

I'm in general agreement with what you are saying. I'll add a further idea that's been rattling around my head on your thread.

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Dr. E (The Real McCoy) wrote on Nov. 2, 2008 @ 19:37 GMT
Hello Carlo,

We miss you!

You write above, "Then there is a post on the waste of public money on research about time in quantum gravity. I take this seriously. Often at conferences I listen to talk after talk, and I wonder "is public money wasted here"? Maybe yes. But was it wasted public money the money that the Ptolemy's Kings put in Ptolemy's astronomy? Or that the Church put in...

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Narendra Nath wrote on Nov. 3, 2008 @ 06:52 GMT
Paul Butler, John Merryman and Dr. E have dominated the scene since my posting of Nov. 01 seeking response of dear author, Prof. Carlo Rovelli to similar lengthy postings prior to November 01. He is still keeping his silence for reasons best known to him.

In the series of essays on 'Nature of Time', we have had two unique theories presented, one TGD by Dr. Matti Pitkanen and the other by the other MDT by your self. Where do we stand to understand the physical universe with respect to the non-physical entity called 'consciousness'. i will appreciatively request Prof. Rovelli to come out with his responding post ,clearing the air filled with lots of historic quotes and lengthy comments, no offence meant towards such postings either!

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Bob wrote on Nov. 9, 2008 @ 10:23 GMT
Carlo, I have a question about unitarity. In the timeless picture you propose there is no unitarity, right? Does this mean that probability conservation can be violated? Bob

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Carlo Rovelli wrote on Nov. 9, 2008 @ 10:42 GMT
Dear Bob,

thanks for the question, which is very appropriate. Let me give a dry answer first, and then explain:

> In the timeless picture you propose there is no unitarity, right?

Right: more precisely, there is no unitarity in the usual sense.

> Does this mean that probability conservation can be violated?

No: probability conservation is not violated.

Let me explain. In usual quantum theories, unitarity is the request that the change of the state *in time* is given by a unitary operator. It follows that probability is conserved *in time*. In a theory in which there is no preferred time variable, this request obviously looses its meaning. This is why unitarity in the usual sense is not present in the timeless formulation. Nonetheless, probability must be "conserved". This means that the probabilities of all the possible specific-measurement's outcomes predicted by the theory must sum up to one. Unitarity in *this* sense must of course be implemented by the timeless theory, and it is.

The answer is different in the statistical context. In this context, thermal time emerges, and therefore we have a unitarity requirement again. In this case, the evolution in thermal time turns out to be unitary by construction.

Thanks also for bringing back the discussion to the actual content of the essay. I do not think that this forum is the proper place for discussing alternative points of view, especially if discussed in other FQXi essays, or issues which are too general.

Carlo Rovelli

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Narendra wrote on Nov. 9, 2008 @ 15:15 GMT
Nov.03 post awaits your response, Carlo. Hopefully , u consider it appropriate for your essay! Parallel between TIME & temperature seems a significant issue. Will you like to give weight to space/time concept over the reality of gravity?

Probability considerations require complete randomness in physical processes. What do you feel if i say ' Order contains randomness but not the reverse of it '?

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Dr. E (The Real McCoy) wrote on Nov. 9, 2008 @ 19:18 GMT
Hello Carlo,

Above you write, "Then there is a post on the waste of public money on research about time in quantum gravity. I take this seriously. Often at conferences I listen to talk after talk, and I wonder "is public money wasted here"? Maybe yes. But was it wasted public money the money that the Ptolemy's Kings put in Ptolemy's astronomy? Or that the Church put in supporting Copernicus...

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Yuri Danoyan wrote on Nov. 9, 2008 @ 23:20 GMT
For best understanding how the Universe working need some time switch of the Time.TIME OUT FOR TIME.

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F. Le Rouge wrote on Nov. 10, 2008 @ 15:11 GMT
I do agree with J. Merryman's refutation above that temperature is not a different kind of scale compared to others based on motion, sun-dial, space, mechanical clock, seasons, Galileo's drops of water, etc.

And I do agree with Narendra Nath objection against randomization. Multiplying static events is not more predictive than dividing them would be past or memory. Dynamics cannot be based on an algebraic 'function'.

Therefore the comparison between 'time' and 'flow' is not 'intuitive' as Dr Rovelli says but a reflexive specific idea on Time that is not shared by many old or new scientists from the Greek Science until today. If this reflexion of Dr Rovelli on time phenomenon is not coming from metaphysics, as it is not physical either, what is it? Just his opinion?

Three quotations of C. Rovelli's essay to prove that Dr Rovelli is mixing physics with arithmetics or algebra:

- CR: 'Familiar physical quantities that disappear when moving to a deeper level of description'

- FLR: Quantities are not physical but legal; they do not 'disappear' but they just change as Fahrenheit are becoming Celsius degrees when you cross the fronteer; the example taken is a 'surface of a liquid': water is 'physical' but not its abstracted 'surface' which is only a poetic or algebraic idea of liquid matter.

- CR: 'Experience shows that we can find mathematical laws characterizing sequences of events (This is the reason we can do science.)

- FLR: 'Sequences of events' are still mathematical laws. Here the argument is redundant and Science based so on tautology. I am not surprised because Central Limit Theory is obviously a tautology too.

- CR: 'In nature, there is no preferred physical time variable t'

- FLR: For sure because there is no 'variable' in Nature. Here is the reason why some scientists think that the problem is to find the adequate scale to make predictions.

The good question is not to use a better ratio, to find the adequate arrow or scale including time but the problem is adequation or equivalency. Why is the Modern Science using so (blindly) interchangeable ratios that drive to exchange Nature or matter with variables like a video-game player hesitating between the virtual reality of his screen and the 'real reality' backwards.

The time subtle 'phenomenon' has become in Modern Science obviously a 'happy hour' for this puzzle of carrots and turnips and their packings together, in Einstein's Theory as in Quanta Physics based on a pre-determinated factor time too.

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Yuri Danoyan wrote on Nov. 10, 2008 @ 20:45 GMT
Time- anesthesia help better understanding anatomy of the Universe.I think is right time and right place forget about time.

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Narendra wrote on Nov. 11, 2008 @ 06:47 GMT
Dear FLR & Carlo,

i tend to agree with most of the points made above by Flr. Huge posts by John Merryman & Paul Butler are mere elaborations of their respective view points in their essays.i personally feel that this competition is not about individual egoism but more about expanding paradigms in science. Also, the latter is not possible if we make scientific methodology static for all times to come. Thus, there is need to broaden one's outlook and possibly make it tend towards the all-encompassing nature, the storehouse of total knowledge. Taking assistance of the non-physical concept of 'consciousness' needs to be welcomed, as our brain/intellect is more than pure physico-biological system.

There are indications about its power in the ancient literature that now requires systematic evaluation based on scientific tools developed. in my essay, i have indicated about such holistic considerations based on my own personal cum professional experience.

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Paul N. Butler wrote on Nov. 15, 2008 @ 06:14 GMT
Narenda;

I see that you have mastered some of this world’s propaganda techniques that are often used by those in low level civilizations to marginalize and attempt to discredit the works of others that one feels threatened by, or does not agree with, or does not understand. These techniques are usually used by those who do not have a good counter argument because those who do have the...

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Narendra wrote on Nov. 15, 2008 @ 06:58 GMT
Dear Paul,

As this is a post on Carlo's essay, may i just go to your essay to respond pleasantly and cheerfully to you comments on the above posting on Nov., 15.You appear to object to the comment i happen to make on very long postings by some authors/commentators!

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Paul N. Butler wrote on Nov. 17, 2008 @ 08:02 GMT
Narendra;

Yes you may (as I mentioned at the end of my previous comment to you, in order to minimize any offence to Carlo)Sorry Carlo. This is me doing a very short comment.

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Narendra Nath wrote on Nov. 17, 2008 @ 12:53 GMT
Carlo's wise silence continues, may well be for the good of us all, provided we contemplate!

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Myke wrote on Nov. 18, 2008 @ 16:35 GMT
Hi all, contemplate indeed! I can see where Carlo is coming from, but the relational elements still require creation in a real (non-virtual) context. The creative cascade from my quantum pseudokinematics (QPK) can be seen as giving either spatial or temporal locations in a constructive context. It just depends on how you like to define the concepts. Even if a quantity is ratiometrically hidden (caused to vanish) it still intrinsically exists, to ghost its consequences...

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F. Le Rouge wrote on Nov. 24, 2008 @ 17:51 GMT
'Non-virtual' or 'No Time': same idea. One can define on this forum three kinds of people:

-Those who do admit the idea of virtual matter and are 'ready to travel in Time';

-Those who think Matter is both virtual and material and have as many subjective ideas to make the link between their 'informational matter' and their 'strong matter'. Rovelli's subjective idea is 'thermic scale' because it gives more solid feeling than the informational Space and speed-scale that Einstein introduced in Physics;

-Those (me) who think that matter can be seen as an informational thing but is not at all. So that it is necessary to let the binary Algebra on one side because it is responsible of the mixing of real Physics with virtual Physics that cannot allow to understand Matter better.

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Narendra Nath wrote on Nov. 25, 2008 @ 07:49 GMT
Dear Carlo,

Considering the merit of your essay on' Forget Time ', i posted many posts between Oct 22 and Nov.11. These were all short ones but in my view it had points directly relevant to your theme essay. However, you preferred not to respond to the specific queries raised therein. May be, you prefer to adhere strictly to your own contents of the essay and any alternate line of approach meets with your silence! May i request finally that you kindly consider the alternates mentioned with your own reasoning for rejecting them all. That will add to the spirit of this open essay contest on ' The Nature of Time '. Otherwise it so appears that you want to reject the theme itself!

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Cristi Stoica wrote on Nov. 29, 2008 @ 14:44 GMT
Dear Dr. Rovelli,

I enjoyed reading your essay.

1. A century ago, physicists tried to make the laws of Physics compatible with the principle of relativity. To do so, they had to “forget time” as a special direction in space-time, to obtain the covariance.

Now, you remember us to “forget time”, proposing an interesting way to do this for Quantum Mechanics.

2. In General Relativity, the time can be easily recovered. Any localized enough system has already a proper time – the natural parameter on that curve. What is missing is the direction of time (positive or negative), and we use for this the thermodynamic time arrow.

3. You propose a thermal time, which also comes with a thermal time arrow. Sometimes, this thermal arrow points in the same direction as the thermodynamic arrow, while in other cases, it doesn’t.

A. For instance, in your example, the Friedmann universe has a special symmetry, which singles out a time direction anyway. Because of this symmetry, I think that is hard to give a general definition of time which differs, on this particular example, from the Friedmann time.

B. But we can easily provide counterexamples. A particle moving through a medium has a proper time, while the thermal time of the total system may be very different from it.



Cristi

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

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F. Le Rouge wrote on Dec. 1, 2008 @ 18:08 GMT
- ‘Relativity Theory’ is not a ‘Revolution’ as Dr Rovelli says and the new idea that the algebraic conventional reference is more real than reality itself was introduced by I. Newton, R. Descartes, C. Huygens, P. Fermat before Planck, Poincaré and Einstein.

The idea that ‘Subjectivity is stronger than Objectivity’ is the same idea. Symmetry, Infinity, Eternity are as many subjective approximations of Nature that is not symmetric, infinite, eternal, contrarily to Einstein theory, CLT, Quadratic equations, cells and vectors of time/space…

This is the reason why the subtle Time, so ‘intimate’ that Dr Rovelli wants to let it on one side with a lot of decency, this is the reason why the Time took bit by bit the lion’s share from C. Huygens until the Travel in Time illusion.

In Descartes 'Natural Philosophy' for example you still have all the stuff: ‘Squaring the circle’, ‘Paradox’, ‘Trigonometry’, ‘Translation of Geometry in Algebra’ and guess what? ‘String Theory’ too.

- Galileo’s or Newton’s pendulum/is not giving any 'special direction' as C. Stoica is suggesting here. Clock is just a rythm, a symmetric oscillation phenomenon and a speed too, that is not the same if you are in the mountain or in the flat country. Galileo used a pendulum for a practical reason in his ballistic experiences although Newton seem to ‘believe’ in the clock reference somewhere.

About the thermic scale: water is not boiling at the same temperature depending from the altitude too.

- Let’s take the Snowboard image: as a group of snowboarders would love to ski. Some want to forget the board material, others the snow matter, but no one the idea of snowboard itself! I do not even speak about dreamers that believe that video games are more real than evrything...

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Dimi Chakalov wrote on Dec. 2, 2008 @ 06:41 GMT
Hi Carlo,

Your Conclusion #4 is "to forget the notion of time all together, and to define a quantum theory capable of predicting the possible correlations between partial observables", which perhaps is related to your statement that "general relativity challenges strongly our intuitive notion of a universal flow of time."

But you stressed in gr-qc/0604045 v2 that "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."

Ergo, GR cannot reject something that is beyond it. Perhaps it would be a good idea if you consult Prof. Karel Kuchar.

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Dimi Chakalov wrote on Dec. 2, 2008 @ 08:21 GMT
P.S. Following the line of reasoning adopted by C. Rovelli, in a fundamental description of nature we must "forget" 3-D space as well, because there is noting in GR to reveal some mechanism producing a spacelike hypersurface with respect to which people talk about "time", as in ADM hypothesis on "the dynamics of GR". In this sense, GR cannot reject something that is beyond it, as stated in my preceding post. Nor can GR explain the apparent time-orientability of spacetime, which also is beyond its applicable limits.

It is completely unclear to me how Rovelli's "patrial observables" can shed light on something that is beyond both GR and QM.

It seems to me that Rovelli's recipe for quantum gravity is this: take Quantum Mechanics and General Relativity in their current formulation, with all their well-known problems, blend them into some new theory with "patrial observables", and hope that the problems of QM may be solved from GR, and the problems of GR may be solved from QM. Don't try to solve any of the initial problems of QM and GR beforehand. Just hope and pray that the "good parts" from QM and GR will cure all problems.

Picture this: you have a car (QM) which runs quite well on some roads, but fails miserably on some essential roads, and a helicopter (GR) that also runs in some favorable weather conditions, but is totally useless in bad weather. Take the car and the helicopter, and build a brand new vehicle, which will run better than the car and fly better than the helicopter, and will also allow you to dive deep into the ocean, as a perfect submarine.

Is this Rovelli's recipe for quantum gravity?

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F. Le Rouge wrote on Dec. 2, 2008 @ 17:08 GMT
'Pray' is the good word in this 'Time Chapel', Chakalov.

I suggest another metaphor: Time is God but Carlo R. does not believe in God and saint Einstein anymore. So he kills the God but keep the ornaments and the Folklore, the saint statue, not to offend people around too much.

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Eckard Blumschein wrote on Dec. 2, 2008 @ 23:02 GMT
Dr. Rovelli,

Please do not mistake it as a personal attack if I ask you to explain step by step how the imaginary unit in your equation (5) relates to our real world.

While we seem to agree on rejecting the widespread belief in an a priori existing time extending for good from eternity to eternity (-oo < t < oo), my suggestion "Let's Benefit from Special Mathematics for Elapsed Time" intends to focus on fertile rather than futile stuff. Maybe I am wrong?

Look at http://home.arcor.de/eckard.blumschein/M283.html for more refutable details.

Regards,

Dr.-Ing. Eckard Blumschein

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Petr Frish wrote on Dec. 3, 2008 @ 12:40 GMT
One thing I like about this Fx contest is certain time inversion: Normally, you read what was published on the topic, and You may find that you can add an original bit to it. Here it seems, one can submit something, and then find out (as a pleasant surprise) that someone already had a similar impression. It may be an illusion, since the terms used do not seem to be strictly defined, but it still feels good. En example:

When you say in your essay (page 3) '.. and notions such as “the quantum state of the system at time t” are quite unnatural in a general relativistic context...' I am happy, to realize I am not the only observer who feels that way.

You suggest an opposite remedy, 'to forget time' then me 'to split it in two' in "One time is not enough" but I am still pleased.

I am still reading all the comments, but I already find another 'pearl of wisdom' - I man something I agree with :-)

'"flowing" time are related to thermodynamics: only in a thermodynamical situation we may have irreversibility, for instance, and we may have memory.'

I would like to make it stronger = a conjecture: Flowing of time a a property of the observer. Any decent observer

of course has a memory. An object (complex particle with no memory) does not experience a flow of time. etc

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Luigi Acerbi wrote on Dec. 3, 2008 @ 23:35 GMT
I completely agree with the basic idea expressed in this essay. Let us forget about time!

In fact, I believe that if we want to understand the deepest laws of physics we have to get rid of all the unobservable quantities -- finding all the "illusory" macroscopic degrees of freedom and then quotienting them away (just like GR and gauge theories do).

Quoting Zurek, this may be called a part of the "epiontic" approach to physics (which I review in my essay).

Thanks for your inspiring work.

L. Acerbi

(The Epiontic Principle..., http://fqxi.org/community/forum/topic/333)

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F. Le Rouge wrote on Dec. 4, 2008 @ 11:42 GMT
Including conventional Time as Superstring theoricians or C. Rovelli do can be seen as much as 'forgetting Time' than 'prescribing Time'.

Second expression is more logic until String Theoricians or Dr Rovelli do not prove that Time is not only a conventional idea but a material one that is grounding the dose of Time. A proof that is obviously lacking here, although the question was -remember- about the NATURE OF TIME.

If a 'pure theorician' does not want to prove that Time is 'something', what I can understand, in this case he MUST prove that conventional Time is dynamics.

Are Boltzmann or Planck telling us anything about the dynamism of Energy or Matter? No, they are just 'quantifying it' that is to say 'squaring the circle'.

We do not know anything more about temperature, energy or matter after Planck than before. Worst than that:idea is growing from here that ballistic measurement (the Wave) is part of Matter although it is only part of ballistic.

To make a comparison: exactly as Walras thought that his economic Diagrams grounded on thermodynamism were part of the Economy.

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Eckard Blumschein wrote on Dec. 5, 2008 @ 23:02 GMT
May I hope for an expert answer, maybe by someone else?

I consider my suspicion serious and - if justified - rather important.

Eckard

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F. Le Rouge wrote on Dec. 6, 2008 @ 11:27 GMT
No expert, please! (Experts are blind soldiers of Empiricism E. Blumschein, taking the differential for the common principle.)

I translated for you a quoting of R. Descartes, father of Empiricism as much as Newton, a quoting that proves that C. Rovelli or Lee Smolin are about three hundred and fifty years late if not more:

"First thing one have to be worried out is that many [Scientists] are mistaking Space idea with Time idea or Speed idea... If I would have link Speed idea with Space idea, I should have give necessarily three dimensions to Force, although I gave to Force only two dimensions to leave out Time.(...)" R. Descartes, September 12th 1638.

All the problems of today Physics are still included in this letter of Descartes who does not solve them but is rationally forgetting Time in Empiricism, that is to say Force, Energy, Inertia and ballistic problems. Rovelli says he is doing it like Descartes but he is keeping Time as a convention! Nothing is more subjective.

Notice E. Blumschein that Descartes is 'anticipating' A. Einstein or H. Bergson attempts to put Time again in Empiricism (probably for cultural reasons, love of poetry and music that are changing the subtle Time in something stronger).

The question of Time and the question of what does Planck say about Einstein and Einstein about Planck, those questions we are turning around and turning around since three hundred and fifty years are in Descartes quoting.

Even if it is difficult to fight against Empiricism or Algebraic Geometry because it gives the illusion of seriousness (3,14 looks more serious than 4 or 3), my opinion is that "experts are dead already". It is still like they are speaking from the Past.

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Eckard Blumschein wrote on Dec. 6, 2008 @ 23:16 GMT
F. Le Rouge,

Even if we are at risk to forget Carlo Rovelli instead of forgetting time, your hint to Descartes reminds me of the fact that Descartes hesitated to introduce coordinates with

not just positive but also negative values. Admittedly I did not read it in the original but in a small booklet on Albert Einstein by Cornelius Lanczos (Loewy) which was translated in Russian language.

I also read somewhere that Fourier was pondering whether or not to integrate not from minus infinity to plus infinity but from zero to infinity.

Furthermore I read an argument of contemporary physicists: Restriction to past time would not be reasonable because prediction is the main goal of physics.

Hopefully you will understand my point of view from 369.

My question to Carlo Rovelli was how do we - step by step - arrive at the complex frequency domain when we start from a measurable, i.e., past function of time? Can complex frequency domain simultaneously include complex time domain?

Descartes did not have any chance but to make the first step by introducing the still ubiquitously accepted notion of Christian time which is also Christin's time. The void future "semigroup" is redundant. That's my message.

Could the consequences be like a purifying lightning? Hopefully I will still witness the failure of LHC to confirm the standard model. I guess, Nimtz will nonetheless continue to claim having proven superluminal propagation of signals.

Physicists are too proud as to take an old engineer serious.



Eckard Blumschein

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Tevian Dray wrote on Dec. 8, 2008 @ 06:59 GMT
As a physical mathematician (the converse of a mathematical physicist), my view of mathematics often differs from my pure mathematician colleagues. Nowhere is this more noticeable than when I teach calculus, which, as traditionally taught, is about functions. But science is about equations, that is, about relations between physical quantities, not about dependent and independent variables.

Never in my wildest dreams did I imagine that all those related rates problems in fact contained a possible resolution to one of the universe's most vexing questions, namely what the nature of time is, or perhaps what it is not.

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amrit wrote on Dec. 8, 2008 @ 14:11 GMT
Dr. Rovelli

yes, time is not a fundamental physical reality

time is an observer effect

yours amrit

attachments: 1_THE_THEORY_OF_ATEMPORALITY__SORLI_2008.pdf

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Eckard Blumschein wrote on Dec. 9, 2008 @ 00:45 GMT
Tevian Dray,

Maybe, you didn't write an essay, maybe I overlooked it. My essay is nearly the opposite of what prefers the majority from Baez to Wheeler. The majority is strong enough. It does not need your support. Why do you deny the distinction between cause and effect in physics?

A key argument of mine is the limitation of original physical quantities to quantities that cannot change their sign.

I am calling it not an equation but an inequality if for instance pressure is always positive except when measured on log scale while sound pressure alternates around the dc component, and the elementary electric charge is negative. Likewise one can not measure negative distance and also not negative duration.

I asked Carlo Ravelli to explain step by step how the i in his equations 5, 19, 24, 26 can be derived from reality.

I was not surprised that he refused to do so because already Charles Francis in spf was also unable to do so.

While they could do it quite easily, they were forced to admit that some strangeness of quantum mechanics could be explained as consequence of improper interpretation of complex quantities.

Apparently they prefer taking quantum mechanics a gospel and deny the elapsed time instead. Carlo Ravelli even suggests to forget time in general. Mors certa, the clock is uncertain.

Eckard Blumschein

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Yuri Rylov wrote on Dec. 9, 2008 @ 10:19 GMT
Dear prof. Rovelli,

I liked your radical approach to a description of physical phenomena. You suggest a timeless description. I believe, that your approach is insufficiently radical. In my opinion, one should use coordinateless description for the space-time geometry. Such a description is used in the Euclidean representation of the geometry, which is used for a teaching in the middle school.

However, the main problem of contemporary physics lies in the fact, that our knowledge of geometry is poor. We cannot describe discrete geometry. We cannot describe geometries with restricted divisibility. We know only axiomatizable geometries, which can be deduced from some system of axioms. However, the axiomatizable geometries form only negligible part of all possible geometries, which are mainly nonaxiomatizable. In particular, the true space-time geometry admits one to consider the principles of quantum mechanics as needless.

Let me explain the situation in a simple example. Let us imagine a person N, who does not know, that the quadratic equation has two roots. (He thinks, that the quadratic equation has only one root). I understand, that such a situation is rather unreal, but nevertheless, let us consider this situation. Constructing theories, the person N may meet such a situation, when one needs two roots of the quadratic equation. In this case he should think about his knowledge of algebra.

But the person N is self-opinionated. He invented new hypotheses, which admit him to compensate his poor knowledge of algebra. These new hypotheses are simple fittings, but in some cases these fittings work successfully. In other situations these fittings cease to work, and the person N is forced to search for other fittings.

Principles of quantum theory and, in particular, the quantum theory of gravity are such fittings, generated by our poor knowledge of geometry. There is a lot of papers on this subject (look in Aricheves, searching my name “rylov”. It is enough). There is also my essay on this contest.

My slogan is: “Find and correct mistakes! New ideas are needless!”

Sincerely yours,

Yuri Rylov

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Adam Helfer wrote on Dec. 10, 2008 @ 23:35 GMT
Dear Carlo,

I've been reading your essay with interest. There are some points I'd like to understand. (Sorry about the long post -- that's what you get for writing a stimulating essay!)

(a) Am I right in thinking that you adopt the Schroedinger rather than the Heisenberg picture in order to try to pass to a theory of quantum gravity? (If we limit ourselves to, say, quantum fields in curved space-time, then the Heisenberg picture is more naturally relativistic, does not distinguish a particular time parameterization, and seems to meet most of your concerns -- although it does not explain the nature of time.)

(b) My main question is, What is the significance of thermal time? Your hypothesis is that this is "what we call 'time'" and "physical time." Since, however, as you emphasize, no relativistically invariant notion of "time" in general, it seems it must be some sort of cosmic time, or time somehow collectively generated by a system. Under what circumstances could we expect thermal time to approach one of our other notions of time?

Suppose I have a simple spin 1/2 system, which I prepare in a (constant) state

epsilon |up>

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Adam Helfer wrote on Dec. 10, 2008 @ 23:39 GMT
[The following seems to have gotten cut off my last post.]

epsilon |up>

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Adam Helfer wrote on Dec. 10, 2008 @ 23:44 GMT
[O.K.; the blog parser seems to be selecting against my states! Here goes again, with less technical notation.]

rho = epsilon (pure up) + (1-epsilon ) (pure down).

After preparation, the system does not evolve (it is insulated). What meaning, then, am I give to thermal time? It does not, with H_rho, generate evolution (the state remains constant). Does it connect with another, familiar, sense of time?

(c) Your program turns on the idea that the system considered is in a statistical state, which reflects "our ignorance of the microstate." How objective is the concept of "our ignorance of the microstate?"

I am guessing that you intend that there is at least a semi-objective way of quantifying this. Two possible approaches occur to me. One is some sort of coarse-graining (as in conventional thermodynamics). If that is what is intended, is it possible to give an idea of what this coarse-graining is?

The other possible approach to objectify knowledge of the microstate would be to consider the effects of quantum measurements as restricting the state. But those lead, not just to statistical restrictions, but to actual projections of a state vector (rather than a density matrix). (One could also consider some sort of mixed approach.)

One reason I am wondering about this is that the thermal Hamiltonian, being - log rho, would be very sensitive to the precise probabilities assigned to very unlikely states. Thus it seems that one has to spell out fairly precisely how to determine the statistical state in order for the thermal Hamiltonian to be well-defined.

Thanks,

Adam Helfer

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F. Le Rouge wrote on Dec. 11, 2008 @ 18:25 GMT
To Blumschein:

-I will read your essay as soon as possible.

-Even if it is more serious from Descartes, father of the Algebraic Geometry to 'forget Time' when you say you want to forget it, although Rovelli is keeping it as nothing less than a dimension!?, nevertheless Descartes is trapped by the Potential Infinity postulate (see my forum) where Black Holes ideology is diverted. There is a Discontinuity in the Standard Model and where Descartes is speaking about 'slipping', Quanta Physics is speaking about 'black holes'.

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mathtew kolasinski wrote on Dec. 12, 2008 @ 02:36 GMT
Hello Dr. Rovelli,

while i can fully appreciate an apparent confusion in identification of relationships in time with time itself and an interest in recognizing that what is referred to as time in physics is typically relative associations and wishing to do away with 't' in considering the relationships (essentially, i see no problems inherent in the math with conclusions 1 and 2), but,...

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Dimi Chakalov wrote on Dec. 12, 2008 @ 03:58 GMT
Regarding my posting from Dec. 2, 2008 @ 08:21 GMT above: Let's recap on the facts.

As of today, Carlo Rovelli's essay "Forget time" got 6 Registered Votes, and 103 Public Votes.

Yet he hasn't made any effort to explain what may happen to 3-D space in case we choose to "forget time". I do hope he will do this until the contest ending date, January 1, 2009.

Please correct me if I got it wrong: In the canonical formalism of today's GR, the foliation of spacetime into 3-D spacelike hypersurfaces enables the distinction of two infinitesimally neighboured hypersurfaces, so if we "forget" about [delta]_t, we must "forget" about the whole 3-D spacelike hypersurface as well. It's a package -- see the drawing attached.

Carlo Rovelli has been manifestly silent on this fundamental issue.

He wrote (Oct. 24, 2008 @ 17:53 GMT): "... I think that in order to have a clear picture the easiest thing is to "forget space" and "forget time", and only to talk about relations between observable quantities."

And in his latest posting (Nov. 9, 2008 @ 10:42 GMT), he added even more confusing remarks: "... the probabilities of all the possible specific-measurement's outcomes predicted by the theory must sum up to one. Unitarity in *this* sense must of course be implemented by the timeless theory, and it is."

It is totally unclear why would the "observable quantities" care about each other's relational stance, nor what would be the driving force that implements the unitarity principle.

For if Nature chooses to "forget time", the "observable quantities" would need human consciousness to get their job done. Or maybe Carlo Rovelli should re-write his essay?

If he chooses the latter, there is a simple way to convince us that we should indeed "forget time": The very mechanism which shapes '3-D space' should be proven non-existent.

Carlo: If you believe can kill the Heraclitian Time, you should first kill the generation of 3-D space.

Please do not "forget" the event of contest ending, January 1, 2009.

Dimi Chakalov

attachments: adm.jpg

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Carlo Rovelli wrote on Dec. 12, 2008 @ 13:11 GMT
Many questons to reply to!

Let me start from the last one, by Dimi Chakalov. Dimi asks "what may happen to 3-D space in case we choose to forget time". And comments "I do hope he will do this until the contest ending date, January 1, 2009." Here I am.

I think that the fate of space is precisely the same as the one of time. I think we better forget both space and time, in order to...

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Eckard Blumschein wrote on Dec. 12, 2008 @ 13:12 GMT
Dear all,

Since Carlo Rovelli has been "manifestly silent", I will take issue concerning some positions by Le Rouge and Yuri Rylov uttered here and comments on Carlo and others made elsewhere. Please goto http://fqxi.org/community/forum/topic/369

You are welcome,

Eckard Blumschein

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Anonymous wrote on Dec. 12, 2008 @ 16:21 GMT
Hi Carlo:

You wrote (Dec. 12, 2008 @ 13:11 GMT): "The result is that some say I am too radical; others, like Dimi in this post, say I am too conservative... I don't know what I am; I am just trying to find tentative solutions to the problems on the table .... "

1. I never said that you are "too conservative". What I actually suggested (Dec. 12, 2008 @ 03:58 GMT) was this:

If you believe can kill the Heraclitean Time, you should first kill the generation of 3-D space.

2. We all are trying to find tentative solutions to the problems on the table, but I'm afraid your approach is logically inconsistent: you "derive" statements about time and space from a theory -- GR -- that cannot say anything about those same statements. Your whole essay is tantamount to speculating on the precise conditions "inside" a singularity, knowing very well that GR cannot be extended outside its applicable limits.

I also suggested you to consult Prof. Karel Kuchar. If he is busy, I can quote from his research papers.

As to your relational ontology, please check out the so-called Buridan donkey paradox.

Dimi

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George Ellis wrote on Dec. 12, 2008 @ 20:27 GMT
Hi Carlo,

Your essay is of course beautifully written and argued. Thank you.

Now in this essay competition, there is an important split between a number of papers putting the view that time is an illusion/does not exist, yours being a prime example, and a number saying time is not an illusion/does indeed exist, mine being in the latter category. Recently I have been under some...

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Chi Ming Hung wrote on Dec. 12, 2008 @ 20:39 GMT
Kudos to George for his accurate and succinct criticism of the timeless view from the quantum gravity camp - you really nailed the issues! Would love to hear what Carlo and others in the timeless camp have to say in response...

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Saibal Mitra wrote on Dec. 12, 2008 @ 21:41 GMT
Professor Ellis wrote about Hamiltonian time evolution: "...there must for example be no dissipative processes happening, including no friction..."

but everyone knows that friction forces arise when we describe microscopic degrees of freedom with which the system is interacting with statistically.

About unitary time evolution, it is not necessary to postulate a collapse to account for any experiments. Unitary time evolution alone is enough, see .eg. here:

http://arxiv.org/abs/quant-ph/0204129

http://arxiv.org/a
bs/quant-ph/0205108

If such a thing as a real non-unitary collapse were to exist, then one sohuld be able to falsify the standard decoherence results based on unitary time evolution in experiments of closed systems.

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Chi Ming Hung wrote on Dec. 12, 2008 @ 22:14 GMT
Saibal,

You wrote:

"it is not necessary to postulate a collapse to account for any experiments. Unitary time evolution alone is enough".

I think this is a common misconception about decoherence. Decoherence by itself does not give a complete solution of the measurement problem, since all components of the mixed state still exist in a global superposition. To account for how this superposition jumps into one of the components in the final step, one has to invoke non-standard interpretations like the many-worlds interpretation.

Thus unitary time evolution alone is NOT sufficient to explain non-unitary quantum collapse, contrary to popular belief.

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Saibal Mitra wrote on Dec. 12, 2008 @ 23:58 GMT
Ok, but the MWI lets the global superposition be as it is, while other "collapse interpretations" need to appeal to new unknown physics that would explain exactly how the collapse happens.

If you assume that measurements leads to a real non-unitary collapse of a wavefunction, then the whole system observer plus measured system inside a hypothetical closed box would evolve in a non-unitary way even if not measured by an external observer outside this closed box.

Since an observer is nothing more than a many particle system, one should expect that closed systems will, in general, not evolve according to the Schrödinger equation. It could be that the deviations from unitary time evolution become large only if the system is large and then the interactions with the environment get large too, making it impossible to measure such an effect.

Now, the fact that only a few papers have appeared that attempt to explain such a non-unitary time evolution from fundamental physics, suggests to me that the people who work on fundamental physics do not take it seriously.

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Adam Helfer wrote on Dec. 13, 2008 @ 03:28 GMT
I am going to break in here because I believe that this exchange between Saibal Mitra and Chi Ming Hung (stimulated by George Ellis) brings to a point some key issues:

(1) In practice people who do calculations in quantum theory rely essentially on projecting the wave vector -- call it collapse or not as you please;

(2) In any conventional interpretation of quantum theory it is only through measurement that we actually learn anything objective about the world (we can only predict probabilities without this);

(3) No conventional interpretation by itself tells us when measurements actually occur or are likely to occur (although various proposals supplementing interpretations have been made);

(4) Decoherence can explain correlations of measurements, but it cannot, by itself, explain the measurements;

(5) The desire to avoid taking up the physics of what precipitates measurement seems to come partly from the fact that it has been little studied, so people are somehow unsure if it is a real question, and partly from a view that if the entire world is really described by quantum theory, then where is there room for a classical measuring apparatus?

It seems clear that physicists should be able to give a physical criterion for when measurements occur, however. This criterion evidently cannot come from within a standard interpretation of quantum theory; it must be a new element. (That does not mean one needs a radically new interpretation; it does mean one needs to figure out what physics is going on.)

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Dimi Chakalov wrote on Dec. 13, 2008 @ 13:01 GMT
Hi Carlo,

I am also going to break in here, because I believe George Ellis made a crucial remark.

George explained his understanding of your claim that there is no preferred time variable in GR (George Ellis, Dec. 12, 2008 @ 20:27 GMT):

"This is correct as regards spacelike surfaces that can represent constant time. But proper time along world lines is indeed a preferred time...

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Peter Leifer wrote on Dec. 13, 2008 @ 15:51 GMT
Dear Carlo,

I've read in some of your replies that you are ready ``forget space-time". In SOME sense it is possible. Please see technical detailes in

http://www.fqxi.org/community/forum/topic/327.

Best regards,

Peter

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Chris Kennedy wrote on Dec. 13, 2008 @ 19:11 GMT
Hi Carlo,

Great essay. I think you do a great job of providing a historical reference frame for this topic before you introduce your own ideas. Very enjoyable.

You argue that the origin of time variable features are not mechanical, rather – emergent at the thermodynamical level. Do you have any thoughts as to how velocity or gravity affect the time dilation of these thermodynamical activities? It seems to me that despite all of the essays, with so many different opinions of time’s true nature – we have only two possible fundamental starting points:

1) That the thermodynamical activity, or motion (or what I refer to as fundamental behaviors in my essay) is used as a measurement of “time” but plays a more passive role because these behaviors exist “in” time and their behaviors are just a visible symptom of what “time” they existed in due to their local environment.

Or

2) What we perceive as time is a macro effect of the most fundamental behaviors among particles, forces and fields. These behaviors define time and in fact are time. Now, if the most fundamental behaviors can all be accurately described as motion, then – okay. But if some behaviors on the quantum level no longer make sense to be described as motion, then it is safer to refer to the fundamental activities as “behaviors.”

For those who commit to the first possible starting point, they would not appear to be in conflict with special relativity – namely Galileo’s principle. The existence of time would be part of the metric that particles and forces exist “in.” There would exist Einstein’s inseparable connection between time and light signal velocity. There would be no “mechanism” - instead, the relative nature of time would just be a co effect of velocity and/or changing gravitational position. Time would exist as a mysterious entity (or co entity) and more questions would certainly need to be asked as to how we could get closer to determining its true nature.

For those who commit to the 2nd possible starting point (which is the one I am committed to) that motions or behaviors define time and in fact are time: Let’s take a system with all of its fundamental behaviors and increase its velocity. These behaviors slow down. If the behaviors themselves “are” time and then become altered as a consequence of their increased velocity- then we need to revisit special relativity. Something is happening on the physical level that we currently don’t have a description for.

Thank you,

CJ

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Vesselin Petkov wrote on Dec. 13, 2008 @ 20:36 GMT
Dear Carlo,

While I tend to agree with George Ellis' objections to your view on how time might be recovered, I do not see how any notion of objective time flow can be saved (let me note that the notion "timeless universe" is misleading; I think it should be "timeflowless universe").

It has been already realized that the traditional view of time flow - as an evolution of a three-dimensional world - is in a direct contradiction even with special relativity (the notion of a three-dimensional world is based on the idea of absolute simultaneity). Then versions of the growing block universe introduced by C. D. Broad in the twenties started to emerge - Ellis, Christian (gr-qc/0610049), Sorkin (gr-qc/0703098). All these versions claim that they do not allow any form of a preferred structure. However, I do not see how this claim can be supported if it is explicitly assumed that the existence of physical bodies is absolute. Then 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. To avoid such an objection Christian proposed that existence should be relativized. To my knowledge, no one has succeeded in providing convincing arguments to defend such a notion.

I have failed to see the justification of what George Ellis wrote that the "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" and also (Fig. 2): "The particular surfaces have no fundamental meaning and are just there for convenience (we need coordinates to describe what is happening)". If existence is absolute, the birthing of events in spacetime does constitute a given hypersurface (again, no matter how complex it might be). Let me stress - I do not mean how we describe the evolving spacetime; the point is what actually happens (and then we can talk about a description) - how the whole network of worldlines grow along the proper time of each worldline (or a family of worldlines). One can also ask additional questions about such an evolving spacetime - e.g. light-like worldlines should also evolve (obviously not in terms of proper time).

Vesselin Petkov

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Narendra nath wrote on Dec. 14, 2008 @ 07:08 GMT
As many people,that many ideas about such fundamental concepts as space and time. Prof Carlo has his and so also the others. To understand the significance of both space and time, let us work out Physics without consideration of these concepts. The reality will remain elusive until we explain the observed facts with alternate concepts. After all the humans evolved these concepts and they are capable of evolving alternate ones. However, there will not be any science without some sort of precepts that lead to some logical concepts. Only then one works out the detailed explanations using mathematical tools to represent the observed facts as also to predict some that still need to be proved experimentally. As measurements will always be limited in sensitivity and accuracy, we still remain bound by such limitations. Thanks to it , we will continue to persue science as a professional activity. However, let us all always remember that we need to continue to build a better human society through our scientific endevours. If we are unable to do so, science may also collapse with humanity. The latter has got a priority over science which is just a professional activity tied to human welfare and basic curiousity about the environment around. Foundational aspects of science are closely linked to human development in a positive direction. Sorry, if it seems like a 'sermon', as i can't claim any such authority!

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Dimi Chakalov wrote on Dec. 14, 2008 @ 14:01 GMT
Addendum to my request for clarification, posted on Dec. 13, 2008 @ 13:01 GMT:

George wrote (George Ellis, Dec. 12, 2008 @ 20:27 GMT):

"But proper time along world lines is indeed a preferred time variable in GR."

May I ask you to clarify the exact meaning of your "preferred time variable in GR" by elaborating on the affine connection. Let me quote from Wikipedia:

"... parallel transport along the curve preserves the tangent vector to the curve, so

nabla_{dotgamma} dotgamma= 0

at each point along the curve, where dotgamma is the derivative with respect to t."

George: Is your "preferred time variable in GR" keeping track on *each point along the curve*? If yes, what is the mechanism of this tracking?

Also, is dotgamma the derivative with respect to some gauge-dependent coordinate time, t, or is it with respect to the proper time [tau] along spacetime trajectories?

Regarding the latter, Carlo wrote (C. Rovelli, arXiv:gr-qc/0604045v2, 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."

I trust Carlo will elaborate on the (timeless?) affine connection as well.

As Alan Rendall acknowledged:

"In elementary textbooks on general relativity we read that the Einstein equations imply that small bodies move on geodesics of the spacetime metric. It is very hard to make this into a mathematically precise statement which refers to actual solutions of the Einstein equations (and not just to some formal approximations)."

Perhaps Carlo Rovelli's suggestion to "forget" time and space is rooted on some 'formal approximations'. Recall Murphy's Law No. 15: Complex problems have simple, easy-to-understand wrong answers.

Dimi Chakalov

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George Ellis wrote on Dec. 15, 2008 @ 05:16 GMT
Discussion of my paper should prefereably be over in my thread, not here, nevertheless as there are two postings over here ask for answers from me, I will answer them here.

Dimi Chakalov, you ask "is dotgamma the derivative with respect to some gauge-dependent coordinate time, t, or is it with respect to the proper time [tau] along spacetime trajectories?" It is with respect to proper time $tau$: which is the meaningful physical time along world lines, and is also the curve parameter for which the geodesic equation has a zero on the right hand side (which is how it relates to parallel transfer).

Vesselin Petkov, 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.

Finally what about evolution along lightlike world lines? yes this can in principle take place; but in my paper I tried to indicate that while this is a possibility, in real situations such as cosmology, signficant effects almost always propagate along timelike world lines rather than null ones. The only physically significant case where influences along null curves are important are in relation to lasers; but they themselves are physical objects that move on timelike world lines.

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Robert Sadykov wrote on Dec. 15, 2008 @ 05:59 GMT
Dear Carlo Rovelli,

Very interesting approach: there is no time - there is no problem. Remaining within the bounds of the special theory of relativity, we cannot refuse the relativity of simultaneity, which concerns to events at a quantum level also. In the general theory of relativity the time plays a key role, therefore the quantum theory of gravitation without time in principle cannot be constructed on the basis of the general relativity. However, hopeless situations do not meet. The quantum theory of gravitation can be constructed as the alternative theory of gravitation. One of many alternative approaches to time and gravitation is presented in essay The Theory of Time, Space and Gravitation.

Regards,

Robert Sadykov

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Lawrence B. Crowell wrote on Dec. 15, 2008 @ 13:33 GMT
I suppose I will throw in my 2 cents on this. I don't think that science can tell us about the existential status of geometric entities. If one considers a point x in spacetime, one can chose two different spatial surfaces S and S' where one pushes this point x to x' and x" which are not equal. General relativity is not about geometric entities, such as points, but it is about the relative motion of particles, such as the goedesic deveiation equation

x^a_{ss} = R^a_{bcd}U^bV^cU^c,

where x_{ss} = 2 derivatives with respect to proper time. So GR does not tell us about the existence of points, or as in the old perspectie "events," but it does tell us about intervals between them (proper time) and permits us to compute the dynamics of particles.

Quantum mechanics and general relativity involve two different notions of time. In quantum mechanics a Hamiltonian is defined by specifying a coordinate time. The Hamiltonian in a Neotherian perspective is the generator of time translations. Yet in general relativity this coordinate time is just a bookkeeping device we impose.

So we are caught with two different concepts of time in our two pillars of physics. There is a third pillar which is thermodynamics, and the so called arrow of time due to the second law of thermodynamics.

In #370 I suggest that time is a scaling principle. Imaginary time t = hbar/kT, for T = temperature in an AdS/CFT setting plays the role of a possible renormailization group. If we think of spacetime as composed of Sakharov oscillators (pregoemtry) the temperature T tells us how many of these modes are excited, which in turn can determine the scaling principle for the phase of spacetime.

I don't know if physics can ever tell us whether time exists or not, but it is an aspect of model systems that is useful.

Lawrence B. Crowell

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Dimi Chakalov wrote on Dec. 15, 2008 @ 14:14 GMT
George,

Thank you for your partial reply from Dec. 15, 2008 @ 05:16 GMT.

Is your "preferred time variable in GR" identical to what you just dubbed 'the meaningful physical time $tau$ along world lines'?

Is the latter observable (=read by a physical clock), or is it "the explicit (but unmeasureable) time" suggested by Bill Unruh?

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

What is your 'test of the pudding', actually?

Dimi

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Alexander Silin wrote on Dec. 15, 2008 @ 17:34 GMT
Lawrence B. Crowell wrote " So we are caught with two different concepts of time in our two pillars of physics. There is a third pillar which is thermodynamics, and the so called arrow of time due to the second law of thermodynamics".

May be, GR operates with ensemble of particles only. On the one hand, the ensemble has statistics of interaction (i.e. it has thermodynamic time); on the other hand it has gravitational mass.

The QM examines wave function microparticle on a background of temperature time of this ensemble.

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Dimi Chakalov wrote on Dec. 15, 2008 @ 20:05 GMT
On Dec. 12, 2008 @ 13:11 GMT, Carlo Rovelli wrote:

"I apologize for the posts I am not answering to. I am tryng to catch up..."

No rush, please take your time. I believe have showed that your approach is logically inconsistent -- please check out my postings above from Dec. 12, 2008 @ 16:21 GMT, Dec. 13, 2008 @ 13:01 GMT, and Dec. 14, 2008 @ 14:01 GMT, and follow the links.

In a nutshell, your logical error would be similar to the following claim: Fish cannot ride bicycles, therefore we should "forget" about bicycles.

More on the intrinsic limitations of GR in my posting to Gavin Crooks from Dec. 13, 2008 @ 20:55 GMT.

Dimi Chakalov

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Adam Helfer wrote on Dec. 15, 2008 @ 20:45 GMT
Dear Carlo,

Thanks for clarifying your use of the Heisenberg representation. (I now see I had too quickly jumped to a misinterpretation of some of your notation.)

I also appreciate your comments that thermal time is meant to get at concepts of flow and irreversibility. If it is possible to be more precise (for example, to say how thermal time is measured, or to what systems the concept of thermal time applies), that would be helpful.

In this connection (trying to understand just what thermal time was) I raised some other questions (about the objectivity of the concept, and about its application to simple systems) in my previous post, and if you get a chance I'd be interested in the answers.

Thanks,

Adam

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Vesselin Petkov wrote on Dec. 16, 2008 @ 02:58 GMT
What does "the real-world evidence" support - an objective flow of time or the block universe view?

As what George Ellis wrote above "the real-world evidence that time does indeed flow is overwhelming" is quite relevant to the topic of this contest and especially to Carlo Rovelli's position I will comment here. But my comments on his statement "Objectively privileged hypersurfaces do indeed...

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attachments: Growing_4D_World.pdf

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Vesselin Petkov wrote on Dec. 16, 2008 @ 03:14 GMT
Correction

I am sorry for this correction (the error was caused by editing at the last moment). The last two sentences of the third paragraph from the bottom should read:

Would this be possible if the rod were a three-dimensional object? Would this be possible if the rod were a growing worldtube (see the attached diagram)?

Vesselin Petkov

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George Ellis wrote on Dec. 16, 2008 @ 12:01 GMT
Dear Vesselin Petkov,

Thank you for the most interesting and thoughtful challenge to the Evolving Block Universe idea that I have yet received. With apologies to Carlo I will answer it on this thread, as you have posted your challenge here.

First you state, “If the evidence is analyzed rigorously it becomes clear that it boils down to the fact that we realize ourselves and the...

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Lawrence B. Crowell wrote on Dec. 16, 2008 @ 14:20 GMT
Vesselin Petkov:

Thanks for your comments. Time and space are what I call relationship structures. They are geometric entities which tie kinematic entities to dynamical ones. As such I tend to suspect that science is unable to tell us in much on whether these actually exist. For that matter the term exist or existence is a bit of strange, and ontological categories appear to have a measure of "relativity" to them.

Fotini has an interesting paper which appears to be getting less attention on how time exists and space does not. I have yet to comment on this paper, mainly because I need to come up with something substantial, but it is curious that one would choose to say time exists but space does not --- an apparent complementary view to Rovelli's. To be honest I wonder if the apparent Carlo-Fotini dualism here suggests something.

The evolving block world might be captured within my Escher disk perspective on AdS. Each tessellation of the AdS is a particular tiling of the spacetime. How each "cell" joins other cells is a way in which a quantum path might split. So a particle which leaves the BTZ black hole horizon the AdS contains, or leaves the boundary at v ~ c will follow an arc or path, but there are at each vertex a set of crossing paths. These are other amplitudes, which in a decoherence or measurement etc may push the particle onto. So in that setting the "block" is the set of all possible paths, but the "evolute" is the particular path a particle may take as it approaches the boundary with v ---> 0.

Lawrence B. Crowell

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Dimi Chakalov wrote on Dec. 16, 2008 @ 15:56 GMT
[My apologies to Carlo for breaking into his thread]

On Dec. 16, 2008 @ 02:58 GMT, Vesselin Petkov wrote:

"Yes, of course, the evidence that time flows is indeed overwhelming, but that evidence is not physical."

If the evidence were physical, there would be some bona fide (Dirac) observable in GR, which would reveal the source and the origin of the "dynamic dark energy", and the ether will come back.

Therefore, we should not expect to catch any *physical* evidence for the flow of time.

You also wrote (ibid.): "... the macro scale evidence supporting the block universe view is overwhelming."

Please see a startling confession by Thomas Thiemann in astro-ph/0607380 v1:

"The puzzle here is that these observed quantities are mathematically described by functions on the phase space which do not Poisson commute with the constraints! Hence they are not gauge invariant and therefore should not be observable in obvious contradiction to reality."

More in my post to Gavin Crooks from Dec. 13, 2008 @ 20:55 GMT.

Dimi Chakalov

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T H Ray wrote on Dec. 16, 2008 @ 16:04 GMT
Lawrence B. Crowell wrote,

"Fotini (Markopoulo) has an interesting paper which appears to be getting less attention on how time exists and space does not. I have yet to comment on this paper, mainly because I need to come up with something substantial, but it is curious that one would choose to say time exists but space does not --- an apparent complementary view to Rovelli's. To be honest I wonder if the apparent Carlo-Fotini dualism here suggests something."

I am curious about that myself, because way back in this thread I commented on that apparent duality coming from the Perimeter Institute, based on Carlo's previous papers on partial and complete observables. I wrote:

"...there may exist theories of complete observables and theories of partial observables that are dual to each other. That is, where a mathematically complete prediction corresponds to the partial observable event probability 1.0. I think that, consistent with Smolin’s theme of 'the present moment in quantum cosmology,' it is the principle of least action that preserves the present moment ..."

I never got a reply, and maybe it isn't worth one. However, I remain curious.

Tom

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Lawrence B. Crowell wrote on Dec. 16, 2008 @ 17:23 GMT
I will try to read Markopoulo's paper again this week. It takes a bit to pick through the list of them here. As I have said there are two different views of time in GR and QM. GR considers the interval as the relevant defintion of time, while QM requires the use of the coordinate time to define wave equations. Of course it might be argued this is an artifact of our representation of quantum states in spacetime more than anything fundamental to QM. On my little #370 space I argue how on a GR frame that proper interval must be measured by some oscillating system which executes some small non-geodesic motion, possibly requiring the use of a coordinate time.

The dualism between our two concepts of time, GR v. QM, might manifest itself under some categorical or functorial map as a matter of either time or space disappears.

Lawrence B. Crowell

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Chi Ming Hung wrote on Dec. 16, 2008 @ 21:57 GMT
Just want to add my 2 cents to the debate between the Block Universe (BU) and the Evolving Universe (EU) viewpoints.

It should be quite obvious that the BU viewpoint is indefensible once quantum phenomena are taken into account. More specifically, the objectivity of indeterministic and probabilistic transitions in quantum mechanics is completely at odds with a BU viewpoint (as pointed out by George Ellis).

On the other hand a EU viewpoint is not at odds with special relativity (SR), because all that's required is that the space-time events, after they've become determinate (through quantum measurement), obey the kinematics of SR, at least in the macro scale. Thus, contrary to popular misconception (e.g. claims by Vesselin Petkov above), SR does not demand the existence of 4-dimensional objects, it only demands that the space-time events which constitute macroscopic objects (like rods and clocks) should obey the kinematics of SR, SR has nothing to say about whether these space-time events are part of a 4-D object, or an evolving 3-D object, or something else entirely.

It is perhaps understandable why Einstein and other classical theorists who denied the reality of quantum phenomena should accept the BU viewpoint, but it's rather inconceivable to me why any theoretical physicist today can still subscribe to the BU viewpoint...

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Vesselin Petkov wrote on Dec. 17, 2008 @ 00:30 GMT
1. My comments on George Ellis' post above will be posted on his thread later today (Montreal time).

2. On Chi Ming Hung's label placing. I believe we all have been enjoying the generally constructive discussions on this forum. Unfortunately, your latest post cannot be regarded as constructive. I would suggest that before criticizing (in your post it is worse - placing labels) a view try to...

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Chi Ming Hung wrote on Dec. 17, 2008 @ 03:03 GMT
Vesselin,

I wasn't "label-placing", merely stating what I think is a misconception, and I wasn't trying to offend anybody, sorry if you took it that way...

And no I didn't ignore your arguments, but I thought I already answered them in my comments... Perhaps I need to elaborate more on what I meant.

Your arguments about length contraction and relativity of simultaneity are classical special relativistic arguments, and based on just that, your conclusion about a block universe (BU) viewpoint is not subject to controversy, but they don't take into account quantum phenomena.

Specifically, rods and clocks are nothing but correlated collections of space-time events. You're correct that nobody knows exactly what goes on in the quantum world which gives rise to these correlated collections of space-time events we call rods and clocks. But it's safe to assume that whatever is going on, we should end up with correlated collections of space-time events which look and behave like rods and clocks in special relativity (SR), because otherwise we can't have faith in either SR or quantum mechanics (QM).

But can we infer from this that rods and clocks are 4-D objects? No I don't think we can, or at least it doesn't serve any useful purpose to do so. The reason I said SR has nothing to say about this matter is because the end results would be the same: there are no 4-D or 3-D objects, only correlated collections of space-time events.

It's true that my arguments are of the hand-waving sort, but until we have a better theory of the transition from quantum to classical phenomena, that's the best we can do for now.

On the other hand, your arguments about length contraction and relativity of simultaneity are also of the hand-waving type because they didn't take into account the quantum nature of rods and clocks.

As for the objectivity of indeterministic and probabilistic transitions in quantum mechanics, the evidence should be abundant: radioactive decay, single-photon double-slit experiment, Stern-Gerlach experiment etc. etc. Yes there have been attempts to explain these as outcomes of deterministic theories (like Bohm's) but only at the cost of introducing yet more hidden unobservable stuff (like pilot waves), so in this case I invoke Occam's razor and just take the evidence at face value...

P.S. While I haven't read your essay in detail, I've read the section "Worldlines and Quanta", and believe it or not, some of your ideas resonate with those of mine, though I don't think they prove the compatibility of BU with QM... But I guess I should comment more about this (and your other arguments like that of the EPR-type experiemnts) later on your essay's forum, not here... In fact I think we should continue this discussion (if you like) in your essay's forum, because it's getting off-topic here...

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Vesselin Petkov wrote on Dec. 17, 2008 @ 06:14 GMT
Chi (or Chi Ming please correct me),

I also think this discussion should continue on my essay's webpage. Here I will briefly comment just on:

"Your arguments about length contraction and relativity of simultaneity are classical special relativistic arguments, and based on just that, your conclusion about a block universe (BU) viewpoint is not subject to controversy, but they don't take into account quantum phenomena."

This is precisely what I mean. Quantum mechanics tells us nothing about the relativistic effects; these are macro scale effects confirmed by experiment. And as Minkowski anticipated these effects and experiments are manifestations of the four-dimensionality of the macro world.

Now, the interesting question is whether the quantum world is a block universe. I think it is, but in order to have a definite answer we need the answer of another question - what is the quantum object?

Vesselin Petkov

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Robert Sadykov wrote on Dec. 17, 2008 @ 10:16 GMT
Dear Carlo Rovelli,

On a way to creation of the quantum theory of gravitation except for time other obstacles can meet. For example, a zero energy density of the gravitational field, as it is presented in an essay The Theory of Time, Space and Gravitation. Gravitational quanta with zero energy will be very strange. Before creation of the quantum theory of gravitation or before creation of the theory of everything the fuller research of properties of the gravitation is necessary.

Yours faithfully

Robert Sadykov

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amrit wrote on Dec. 17, 2008 @ 15:41 GMT
Dear Dr. Rovelli

You say: In short, I propose to interpret mechanics as a theory of relations between variables, rather than the theory of the evolution of variables in time.

I would say: Relations between variables run into atemporal space. We describe them in time as a mind model.

yours amrit

attachments: 1_Phenomenology_of_Time_and_Quantum_Gravity.pdf

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Dimi Chakalov wrote on Dec. 18, 2008 @ 11:22 GMT
Vesselin Petkov wrote on Dec. 17, 2008 @ 06:14 GMT

"Now, the interesting question is whether the quantum world is a block universe. I think it is, but in order to have a definite answer we need the answer of another question - what is the quantum object?"

Regarding this "interesting question", please notice my posting from Dec. 15, 2008 @ 20:05 GMT, about fish and bicycles.

As to "what is the quantum object?", please check out the fist posting at George Ellis' thread, from Dec. 2, 2008 @ 07:02 GMT, and my latest posting there, from Dec. 18, 2008 @ 10:59 GMT. It's all about an _arrow of spacetime_ . We should not separate time from space -- recall Hermann Minkowski.

Dimi Chakalov

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Dr. E (The Real McCoy) wrote on Dec. 20, 2008 @ 22:27 GMT
Hello Carlo,

Hope all is well!

In this BBC video, Lee Smolin states, "Einstein taught us that space is not a background that things move in. Spoace is a network of relationships that are ever dynamical, ever evolving, part of the world. The geometry of space evolves and changes--WIGGLES--just like anything else==just like electromegnetism, just like...

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Chris Kennedy wrote on Dec. 22, 2008 @ 15:04 GMT
Do I smell a potential confrontation brewing here? I haven’t seen anything like this since Apollo Creed tried to get Rocky Balboa back in the ring for a rematch. Can you imagine the excitement that a debate would bring:

Ladies and Gentlemen – Now for the main event. In this corner, we have our challenger:

He’s the master of moving dimensions – Elliot “The Real McCoy” McGuckennnnn!

And in this corner: With the best overall combination of restricted and public votes so far - The Thermodynamical Wonder – Carlo “Leave your wristwatch at home” Rovelllllli!

Okay guys, normally, I would recommend a twelve round debate(three minutes each) but since none of us are sure of what the nature of time is yet - just come out typing when you hear the sound of the bell and keep going until we have a winner.

Good luck!

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Narendra Nath wrote on Dec. 22, 2008 @ 16:43 GMT
Vasseline, George and Rovelli,

What is deterministic in this Universe is the Universe itself with whatever it unfolds before us. Science of Physics is not deterministic , as it attempts to evolve some concepts to understand what is observed to be happening in this universe of ours. We only try to understand how the things are happening and not the why's. The observed facts are supreme and any theoretical model that we may evolve based on limited facts and not the entirety of observed facts. That is we need consistency when we explain one phenomenon, with explanations provided for other observed phenomena too.

As i understand it, the block universe and the Expanding Block Universe are one and the same. It is just a difference that in the former time is a parameter while in the latter it is intrinsically built into the explanation. Thus, i don't see any scope for personal confrontations, as our individual opinions have little significance unless born out by experimental facts that have been confirmed reasonably well by independent research workers. That much is enough as we seek better and better relative truths in Physics about the various physical phenomena as such. May i just say that it may not be wise to conclude that we have understood the working of the human brain fully through Physics 'alone'. The human mind and the human 'soul' do not entirely lie in the domain of current Physics. The Nobel winner, Prof. Eccles of Oxford while studying the neuron activity of the Supplementary Motor Area (SMA) of the brain observed activity when none was expected from within the body involved. He asserted that there appears to be a non-physical sheath that surrounds the SMA that is capable of recording such outside interactions that the neurons in SMA are experiencing. He further believes that this non-physical covering survives with such a record of 'outside interactions' beyond the death of that body!

Let us therefore keep our discussions open in a reasonable way to permit later innovations, instead of making categorical statements about the finality of any approach or explanation. i am sorry if anyone takes me as personally critical of another person, as i myself can not be absolutely sure about things that i am supposed to know well.

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amrit wrote on Dec. 23, 2008 @ 15:11 GMT
Der Dr Rovelli

Science can not exist without time, we just have to give time right position in scientific models of the universe.

My recent idea is that time is a "coordinate of motion".

Theory of Relativity describes motion of elementary particles and massive bodies. With clocks one measures duration and numerical order of this motion. Time is what is measured with clocks: the duration and the numerical order of motion of elementary particles and massive bodies in space. In the Theory of Relativity time as a “fourth coordinate” describes motion of massive objects and elementary particles in space. In that sense fourth time coordinate is the “coordinate of motion”. Time is not a part of space. Space-time is not a physical reality into which material change run. Space-time is a math model only used for description of motion of objects in space where time is a coordinate of motion. Space itself is atemporal.

attachments: In_The_Theory_of_Relativity_Time_is_a_Coordinate_of_Motion__Sorli_2009.pdf

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Narendra Nath wrote on Dec. 28, 2008 @ 05:52 GMT
Awaiting response if any on my post of Dec., 22, 2008

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F. Le Rouge wrote on Dec. 31, 2008 @ 19:55 GMT
- Opinion of C. Rovelli (December 12) that one can easily get rid of Space at a fundamental level... this opinion is just incredible!

It proves that Rovelli's algebraic idea of Space is based... on Time idea (Words/Language), no matter the kind of scale he is choosing, boiling water in a valley or on top of a mountain.

- Of course Aristotle has nothing to do with Rovelli, Aristotle for whom Space IS Matter, Water, Ether or other elements. Time is for Aristotle deforming Matter.

- But Descartes cannot be quoted here by Rovelli either. Descartes wants to get rid of TIME in his ballistic ('Essay on Static') experiences. Even if Descartes did not understood some of Aristotle's lessons, he is aware of the relationship between matter and space that Scientists mostly are stating: distances in the Universe are often deduced on Spheric Earth or Moon dimensions; and if World is not 'fundamental'?

- And Newton cannot be asked for help by Rovelli too, even if Newton principles are somewhere ambiguous like Descartes principles. Here must the metaphysical Ether be evoked because Space is collapsing on this point (Is Ether full or empty Space?).

Debate between Huygens and Netwon about Ether is Christian metaphysical Debate.

- Rovelli has more to do with G. Berkeley for whom language is more real than reality itself, or with Einstein General Relativity (and E=mc2 in which matter and space are conjured away). Problem of Rovelli is that he wants to forget Einstein on whom he is based. He is catched in the reference as a fly on a web.

'Dualism' of Rovelli or String theoricians is this one: when he is speaking about metaphysics: this is ballistic science; but when he is speaking about ballistic science: this is metaphysics.

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F. Le Rouge wrote on Dec. 31, 2008 @ 20:08 GMT
When you tell me that my point of view is 'refreshing', Narendra Nath, do you mean like the refreshing comment of the child in the Andersen Tale: 'But the King is naked!'

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Narendra Nath wrote on Jan. 1, 2009 @ 13:47 GMT
Le Rouge, i just mean that it is both meaningful and innovative, with little bias from what is 'known'. i am not familiar with Anderson Tale, may be i have forgotten. Therefore, your quote from there is out of context for me. Never mind, the essay discussion soon closes and i wish you and all other authors the best of life ahead.

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Member A. Garrett Lisi wrote on Jan. 2, 2009 @ 03:12 GMT
Hello Carlo,

I've been impressed by your thermal time hypothesis ever since I first encountered it in your book. And here you've done an excellent job of presenting it with some fresh points of view. Thanks for this contribution.

Best,

Garrett

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F. Le Rouge wrote on Jan. 3, 2009 @ 14:02 GMT
- I want to be clearer on the big mistake that Carlo Rovelli is making about Aristotle's Physics.

Opinion of Rovelli is that space is empty.

Opinion of Aristotle is that space is full (of matter).

As there is no emptiness in Aristotle's Physics drives Rovelli to think that there is no space in Aristotle.

Therefore Algebraic method is deeply criticized by Aristotle.

- What is the problem with such a mistake about Aristotle? The problem is that you cannot understand Newton, Huygens or Descartes without understanding Aristotle. Newton principles are not entirely logic but he is partly sharing with Aristotle the idea that space is matter, especially on the hot spot of Light which is for Newton Matter. Idea of Light beeing both a wave and a particle is a nothing else than a Compromise.

- About G. Lisi's Theory that I dicovered in French press, close to D. Bundy's Theory in this forum, I notice that this theory is not far away from Rovelli's.

What did Descartes do? He translated Geometric drawings in Algebraic numbers (History of Art/Painting from XVIIth is governed by the same idea). What are Lisi or Bundy doing? They translate Algebraic numbers in Geometric drawings.

Why this symmetric turning round? Because of the cul-de-sac of fundamental Mathematics.

And Albebraic geometry is for sure more difficult to call in question again for Modern Mathematics than for his Creator to kill Frankenstein (New metaphor for open-minded Narendra Nath).

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Gianluca wrote on Jan. 5, 2009 @ 01:30 GMT
Dear Prof. Rovelli,

I find your views about time extremely clear and rational and you contributed in developing my understanding of a world ontology not dependent on time. Now I hit randomly a short text by Lee Smolin at http://www.edge.org/q2009/q09_9.html#smolin where he affirms with sudden certainty presentism & time realism. Since you know well Lee Smolin, do you know which could be the rational basis of such a radically opposite view and which is your viewpoint on it? Please restore my shaken faith in a timeless reality (is Lee the Devil?)

Sincerely, and I wish you a happy 2009.

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Dr. E (The Real McCoy) wrote on Jan. 7, 2009 @ 23:13 GMT
Happy New Year All!

I too recently came across Lee's piece:

http://www.edge.org/q2009/q09_9.html#smolin

"THE LIBERATION OF TIME"

Moving Dimensions Theory has been liberating time for quite some time now. Check it out where I used the word "liberate" at:

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

"Dr. E wrote on Sep. 11, 2008 @ 15:18 GMT

...

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Narendra Nath wrote on Jan. 9, 2009 @ 07:03 GMT
Dear Le Rouge,

On this essay post,you have raised me to the level of Frankestein, an open minded monstor. i would have liked you to leave me at a much lower level. What you feel we know about the universe through science at present? i may say we know a negligible amount, inspite of the 'tremendous'progress science & technology, its sister, has made! Without the broadest of thinking one can never expect to overcome the huge gap between total knowledge and the existing knowledge that we have attained about the Universe. We often find that what we knew in science about the moon, the nearest object to the Earth, changes drastically as we perform more and more expts. on the moon with the instruments. The latest mission has been done by India and it has succeeded in identifying the sources of water and helium3 on the moon.That si going to provide a big boost to exploit the resources on the moon for our comfort on the earth. This will go on and i know we have lot of surprises in store for us about our sister planets on our solar system too than what we claim to know presently. Thus, it is best to say we know very little and keepmour minds open for future unknowns that exist in plenty.

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F. Le Rouge wrote on Jan. 9, 2009 @ 09:20 GMT
- 'Open minded', Narendra, because I bet with my friends before this contest that no one on the fqxi forum would talk with someone (me) who says that Engineering is not Science but a bad mixing of Technology and -let us say- 'Ballistic Metaphysics'; with someone (me) who says that Isaac Newton is wrong, especially his gravitation Theory. (But if you read Newton's principles you will see that Rovelli does believe more in Newton that Newton himself believe in gravitation.)

- 'Frankenstein' because Algebraic geommetry is a monster, entirely created by Scientists and who is 'escaping' now. Two examples:

. Usefulness of fractal numbers for instance is entirely subjective, related with the attempt to square one's circle. But notice that this 'subjectivity', Narendra, has become almost objective.

. Second example is Feynman when he says something like: 'Nobody is able to understand Quanta Physics': I translate: nobody is out of the reference, the ratio between engineers and the machine. Again: This is Pythagorean Science and its monster Frankenstein!

- You are sharing the same paradox than Rovelli: he is wanting more 'objectivity' and less 'cognition' and so suggests to forget the Time... but he keeps it although as nothing less than a World dimension! It is difficult to be more subjective, please admit it. And because Aristotle has not the same idea of (empty) Space than Rovelli, does it mean that Aristotle does not care about Space?

You are closer to Einstein or Bergson, Narendra, who intended to put more Spirituality in Empiricim, to put more Time in Mechanics. Due to your Indian Natural Philosophy I guess, you are not far away from the lutherian spirituality that inspired Huygens or Einstein: as death is just a 'new start', Time is not a negative value for you. You do ignore another kind of spirituality in which Time is a negative value, a kind of 'Sympathy for the Devil'.

- When you say that Technology is the Sister of Science, you should not forget that millions of people that did not share the ballistic spirituality died because of it.

I make one's peace with you here Narendra, on the huge gap between total knowledge and what Engineers think the real World is throughout their computers and lenses.

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petm1 wrote on Feb. 18, 2009 @ 22:44 GMT
Think of our clocks as measuring the intrinsic motion of the same systems governed by the laws of thermodynamics. Think of our clocks as counting the events, and temperature as a measure of the duration of the events themselves. The shorter the duration of an event the more events you can fit into the same amount of time. With these two ways to measure the present wouldn’t you think that the rule of local clocks ticking at the same rate, and thermal equilibrium might be two ways to look at the same thing?

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Dr. E (The Real McCoy) wrote on Feb. 25, 2009 @ 15:11 GMT
Hello Carlo!

Hope all is well with you!

Just reread your paper and I got to thinking that quantum gravity is indeed the father of so many wrong directions--from Einstein's later years whence he abandoned *physical* models in favor of pure math to String Theory to LQG. Too often quantum gravity is treated as something *real*--its existence is assumed to be *real*--and this...

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attachments: 1_ja_wheeler_recommendation_mcgucken_medium2.jpg, 1_physics5.pdf

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amrit wrote on Mar. 18, 2009 @ 18:32 GMT
motion runs in timeless universe

time has origin in the human mind

with clock we measure duration of motion in timeless universe

attachments: 5_ETERNITY_IS_NOW_Sorli_2009.pdf

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Wilton Alano replied on Jul. 4, 2010 @ 18:31 GMT
Dear Amrit,

Time means that matter in motion is - in the 'present' moment - in a different spacial position than 'before'. As you must know, it happens to any corpse or particle spinning or in spatial trajectory.

So, time means that a system is energized and, therefore, in motion and truly real; instead of a just "an human mind construction".

(* "Energy" means inertial motion of corpses or particles).

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Alejandro Rivas-Micoud wrote on Dec. 30, 2010 @ 09:28 GMT
Dear Dr. Rovelli,

What if time is simply the means by which random chance “collapses” a wave probability for a specific segment of space/matter? In other words, is entropy simply the means by which gradually a set of probabilistic outcomes randomly occur throughout space? Thus making time a consequence of random chance gradually collapsing from its wave function into an observable state? The past as observed “collapsed” particles? The future as non observed probability waves? The present as observation of the collapse of a specific space/matter segment? Energy, the consequence of observation? Matter, the result of the action of time on space? In other words, if the future were known, then time would not exist?

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Rodney Bartlett wrote on Jan. 30, 2011 @ 12:32 GMT
Dear Dr. Rovelli,

Here's a post that tries to comment on FQXi's 2008 essay contest (The Nature of Time) as well as its 2010 essay contest (Is Reality Digital or Analog?)

We have to wonder if the Large Hadron Collider was worth all the time and money it took to build. It won't find the Higgs boson. It may well "prove" that strings exist but this will only deceive the world because...

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Rodney Bartlett wrote on Feb. 2, 2011 @ 03:27 GMT
I know I can't submit another essay. I don't plan to - these are just some comments that came to mind after thinking about my essay. They don't seem very relevant to the topic "Is Reality Digital or Analog?" but writing them has given even more satisfaction than writing the essay, and I'm in the mood to share them with the whole world. So if you've got time to read them...

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Rodney Bartlett wrote on Feb. 7, 2011 @ 02:58 GMT
According to the Community Ratings, my essay in the 2011 Essay Contest is sliding further down the ratings each day. But I'm having more luck with a science journal called General Science Journal - comments of mine inspired by the essay (which are nearly 20,000 words long and include comments about "The Nature of Time" as well as "Is Reality Digital or Analog?") were published in the Journal on Feb. 6 and may be viewed at http://gsjournal.net/ntham/bartlett.pdf

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C allen wrote on Oct. 27, 2011 @ 13:53 GMT
Carlo, I was so relieved to read the truth about Time. For a long while I have understood that time is just a measurement.

Archaic thought - a bit like all the ' sun ' language.

The sun is going behind a cloud, the sun is rising etc -

Somehow we are in danger of losing common sense.

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