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Is Reality Digital or Analog? Essay Contest (2010-2011)
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On the Depth of Quantum Space by Daniele Oriti
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Author Daniele Oriti wrote on Feb. 16, 2011 @ 14:23 GMT
Essay AbstractWe focus on the question: - Is space fundamentally discrete or continuous? - in the context of current quantum gravity research. In particular, we paint a scenario based on the idea that quantum space is a sort of peculiar condensed matter system, and on the speculation that its microscopic (atomic) dynamics is described by a group field theory formalism. We suggest that, from this perspective, on the one hand the question has no absolute meaning, so no answer, but also that, on the other hand, the reason why this is the case is the quantum space is much richer and more interesting than we may have assumed. We also speculate on further physical implications of the suggested scenario.
Author BioBorn - Messina, Italy - Italian PhD - Univ Cambridge 2003 Postdoc - Univ Cambridge, Univ Utrecht, Perimerter Institute AEI senior researcher and leader of independent research group ''Microscopic Quantum Structure & Dynamics of Spacetime'' Sofja Kovalevskaja Prize awardee (A. Von Humboldt Foundation) (2008)
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Georgina Parry wrote on Feb. 18, 2011 @ 07:34 GMT
Dear Daniele ,
A very clearly written account of an interesting topic. You set out what you would be considering and the proceeded to do so in a way that smoothly carries the reader along. I did like the recurrence of the theme "it depends". You are so right it does depend. I came to the same conclusion at the end of my essay but you said it so much more clearly. The repetition not only tied the essay together but drove home how important that is. It is not a black or white question at all and the answer does depend in part on what is intended by the question when it is asked.
I do hope you get lots of interested readers who can give you feedback on the physics content. I think you did well to make this topic so accessible and educational to a non specialist and therefore enjoyable too.
Good luck, Georgina.
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Anonymous replied on Feb. 21, 2011 @ 19:51 GMT
Hi Georgina,
thanks a lot for your kind words and appreciation. I will try to read as many a possible of the other essays submitted, and especially yours, and hope to have something interesting to say about it.
Thanks again.
D
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Yuri wrote on Feb. 20, 2011 @ 20:18 GMT
Dear Daniele
My essay http://www.fqxi.org/community/forum/topic/946
contain some terahedron"s logic idea.Do you see something common with your triangles?
All the best
Yuri
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Author Daniele Oriti replied on Mar. 13, 2011 @ 16:41 GMT
Not really, at least at this point.
best,
Daniele
Johan Noldus wrote on Feb. 26, 2011 @ 21:08 GMT
Dear Daniele,
I don't know of any physicist anymore in these days who would say that atoms are discrete ; isn't the main lesson of relativity that even the number of atoms is not well defined (and that the notion of particle itself is contextual)? Likewise, nobody would argue that a gas is somehow discrete and a fluid continuous merely because we can give such effective descriptions. Fact is that QFT is defined on a continuum (I know very well some version of it can be constructed on causal sets) and the whole rationale behind it comes from causality, locality, statistics, cluster decomposition and Poincare invariance. You adress none of these issues, neither do you indicate what group field theory can contribute to the status of them. Second, your comparison with condensed matter models is misleading since these are all background dependent; nobody knows how to recover a manifold structure in a background independent way since it requires local observables. The problem here is that you cannot define these in a canonical way. Moreover, you adress none of the philosophical problems of quantum spacetime (which actually make the whole idea rather unlikely).
So, I hope that you will say that the limitations of the contest format prohibited you from treating all these issues and that you can explain how you see them.
Kind regards,
Johan Noldus
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Anonymous replied on Mar. 5, 2011 @ 19:45 GMT
Dear Johan,
thanks for you comments and interest, and sorry for the delay in my reply.
It is certainly true that the limitations of the essay format implied that I could not touch on all of the aspects of the problem that I would have like to, and that even those that I discussed could have been explained and treated in much more detail and more satisfactorily. However, it would not...
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Dear Johan,
thanks for you comments and interest, and sorry for the delay in my reply.
It is certainly true that the limitations of the essay format implied that I could not touch on all of the aspects of the problem that I would have like to, and that even those that I discussed could have been explained and treated in much more detail and more satisfactorily. However, it would not be honest to blame these limitations for any shortcoming of my essay. My own limitations in knowledge and expository skills are what I am more concerned with and what I, like everyone else, should try to improve on.
Let me try to clarify a bit more my thoughts on this matter by replying to your comments, which I am not sure I really understand though.
First, as a general comment on atoms, gas, fluids and condensed matter systems, I do not claim to have written anything original on any of this, in my essay. The parallel with atoms and condensed matter systems is indeed used only to exemplify, using familiar concepts, a certain picture of quantum space that cannot be as familiar, because of the more exotic nature of the subject, and the more limited comprehension of it we have.
So I agree with your comment that the limited, not absolute, purely effective nature of our description of atoms as discrete, of a gas as discrete or of a fluid as continuous is agreed upon by any physicist. Again, I am happy we agree on this because I was not trying to say anything original here. However, I also think that any physicist would agree that 'atoms are discrete' in the 'effective, limited' sense that there exists circumstances (e.g. relativistic effects should indeed by neglected to some extent) in which the physics of a system is well-described by a few discrete entities behaving like particles etc. Same for field theories around the Fock vacuum in flat space at low orders in perturbation theory etc. The fact that this effective description, valid in some circumstances, has to be replaced by another in which the same system is described by a continuous medium, for example, in other circumstances, is exactly the rationale behind my 'it depends' and, as I tried to explain, rests indeed on the characteristic properties of QFT.
Then you say something crucial: ''Fact is that QFT is defined on a continuum''. Indeed. This hints at the fact that it is this underlying continuum spacetime that one is considering as being 'fundamentally so' or, alternatively as 'fundamentally discrete' in nature, e.g. described by a causal set.
The main point of my essay is that one can 1) take the fundamentally discrete entities constituting spacetime at the quantum level in some approaches to quantum gravity (lattices, graphs, possibly also elements in a causal set, etc); 2) re-interpret them as 'particles', 'atoms' of space in analogy with the 'real' ones of condensed matter systems; 3) describe their dynamics in terms of a field theory that is not defined on any spacetime itself but rather on some internal, auxiliary, meta-space (call it as you like), the group manifold; 4) have as a result the same richness of different phases and effective descriptions (continuous, discrete etc) for spacetime that one has for condensed matter systems.
This means that the same limited validity of both the continuous and 'atomic' description of fields in QFT or of condensed matter systems will hold true for spacetime itself. Thus, the question of whether spacetime is discrete or continuous can only have answer 'it depends'. And the question whether it is either fundamentally one way or the other can only have answer 'no', because neither description would be fundamental, as you correctly say for atoms or gases or fluids.
To try to argue for the above point of view was the main goal of the essay.
You mention several important issues, related to the fundamental status of several features of QFT on flat space, like causality, locality, statistics, etc and ask whether GFT contributes to our understanding of them. For some of them it does, and I can only refer to the literature for all current work. The object of the essay, you would understand, could not be to address these issues. Certainly, GFT denies their validity at a more fundamental level, because they are very much tied to the background dependent description of ordinary QFT.
However, we are very far from being able to show how they emerge from a purely background independent description of space (e.g as the one of GFT). The theory is very incomplete, and indeed the main open problem, as far as I can tell, is to prove that a continuum description of spacetime and General Relativity (and thus special relativity) arises from GFT.
As you also say, nobody knows, at present, how to do this. However, I do not see why this inability should be mistaken for impossibility (either in principle or in practice) and thus invalidate the picture I tried to paint, beside the fact that obviously much more work is needed to validate it (and actually, also to refute it). Again, for all the current work on this issue, which I mentioned in the text, I refer to the literature (e.g. that on GFT renormalization, on the extraction of physics from spin foams, on the effective non-commutative field theories obtained as perturbations of GFT solutions, etc).
The comparison with condensed matter is indeed just an analogy, as I stressed in the text, possibly useful to guide us towards a better understanding of quantum space, but I agree it cannot be taken literally because our condensed matter theories are (as they should be, given that real condensed matter systems live in our labs) based on a fixed, flat spacetime.
Finally, I am well aware of the many philosophical issues raised by the very notion of quantum space, and of all those intertwined with every aspect of quantum gravity research (and even before that, with Genera Relativity and Quantum Mechanics themselves). However, first, I do not see how these issues (all currently and hotly debated among philosophers and physicists) make the 'whole idea' unlikely; second, to discuss these issues was not the scope of my essay, focused on a much more limited question and trying to achieve a a more limited goal: to present and argue for the general picture I outlined again above, in the hope that it could be stimulating and inspiring for further research of others as it is for mine.
Thanks again for you interest and comments and do not hesitate to put forward more of them or any specific doubt or question. I would be happy to discuss any such specific issue.
Best,
Daniele
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Johan Noldus replied on Mar. 6, 2011 @ 09:18 GMT
Dear Daniele,
The problem of quantum gravity is to give a description of nature which is in principle valid on all scales (this is by no means in contradiction with renormalization). So your answer that it depends upon the scale or system is unfortunately not valid. You seem to take the point of view that the observer(s) are somehow living in ''meta space'' and that the theory should...
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Dear Daniele,
The problem of quantum gravity is to give a description of nature which is in principle valid on all scales (this is by no means in contradiction with renormalization). So your answer that it depends upon the scale or system is unfortunately not valid. You seem to take the point of view that the observer(s) are somehow living in ''meta space'' and that the theory should adapt to the ''glasses'' they are looking through. Of course, this is what you get when you naively combine quantum mechanics with general relativity which is what brings me to another point of yours where you say that you do not understand how these issues make the whole idea of ''quantum space'' unlikely. As I said, the main problem is how to define ''local observables'' in a ''canonical way'': there exist very good (read: almost conclusive) no go arguments against the mere possibility for even doing this. This issue is intertwined with an observer living inside or outside the universe and it would take pages to explain it in any detail. What surprises me however is that you deny that while this is an open problem for 80 years now (indeed, so long) it most likely implies that it does not work that way (and indeed, I know it doesn't).
Moreover, I guess you start from space and not space-time right? But even on a much simpler plane, you could insist that strict locality is a property of nature; this immediately rules out all the exotics you are willing to consider (so here you have a deep physical reason). The problems with the kind of models you are considering are legio and most importantly, they lack physical insight and motivation. Let me give you a few examples : free QFT on flat space-time is exactly correct without any doubt. For example, it almost canonically follows from: (a) locality (b) causality (c) isotropy and homogeneity of the vacuum (d) 4 dimensions (e) cluster decomposition (f) Hilbert space representations of the symmetry group (g) positive energies (h) statistics. If you think about it for a while, then you recognize that every single requirement is physically mandatory for the limit of zero interactions. Therefore, you have to think about how you are going to build an interacting theory but the latter should have many foundations in common with the free one. Just as plain Minkowski is the short scale limit of general relativity, the free theory should be the short scale limit of the interacting one - so we should have asymptotic freedom and not merely asymptotic safety. A first step in that direction would consist in giving interacting quantum theory itself an Einsteinian (meaning local and fully covariant) formulation. This is a necessary exercise in order to put both theories on the same level. You may imagine that the interacting theory will not be causal, have more exotic statistics and not satisfy the cluster decomposition, but all this should by dynamical: it should follow from the physical requirements of covariance, asymptotic freedom, locality + the conditions on the free theory. GFT probably satisfies none of those requirements (including covariance!) and I haven't seen a good principled analysis nowhere in the literature.
So, what do people do? They go in defense mode. They even start to deny that the free theory is a physical limit. This of course is utter rubbish, why in principle should nature not be capable of playing around with the gravitational constant (or the Planck constant or the speed of light) ? You may think about c as a definition of a second starting from a meter, G as a conversion between mass and a meter and hbar as setting the scale for the meter itself. So again, it appears totally obvious to me that the limit of zero G in theory space should exist (as well as the limit of zero interactions) and it is the knowledge of that limit which should be a foundation of your theory just as special relativity is for general relativity in the Palatini formalism and just like classical mechanics is for quantum mechanics in the deformation quantization approach. This is actually also the case for the thermodynamic limit of absolute zero; there have been numerous attempts like stochastic vacuum field fluctuations as an alternative to QED and a big chunk of the physics is determined by the T = 0 limit. This is something which is fundamentally lacking in all approaches to quantum gravity (except one) and it is a big mistake.
Kind regards,
Johan
PS: I do not care about how you write things, expository skills are a matter of social convention and I have never cared too much about what others ''think''. What I do care about is what you write and as far as I can see, you repeat all the hopes and ''misconceptions'' I have heard for more than 10 years.
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Johan Noldus replied on Mar. 6, 2011 @ 11:24 GMT
Dear Daniele,
Now that I see, I did not respond yet to a few points of yours. So, you admit the notion of a particle becomes superfluous in the context of relativity: therefore, why are you doing your best to reinstate this concept in a theory of quantum gravity?! Shouldn't you just do the opposite and move even further away (that is further weaken) from the concept of a particle than it is the case in QFT on Minkowski? Furthermore you imply that conditions like causality, positive energy and statistics are background dependent concepts... they are not by any means. You confuse the principle here with its implementation in QFT on Minkowski; actually, from the latter we know they are independent issues even in this weakened context. By this, I mean that, for example, one can drop positive energies and still get a causal QFT with the right statistics. If you think about it deeper, you will need a principle for having an arrow of time (positive energies) and independently you will need to specify the statistics (that is the very nature of quantum mechanics). Probably, you would need to specify the spin-statistics relation (all research to a spin statistics theorem in quantum gravity points in that direction) as well. So, you still need three independent principles and you haven't gained anything.
The problem is that you assume a priori that gravity has to be quantized like any ''particle'' does. You care to give a good physical motivation for this, apart from saying that ''quantum theory as we know it should be universally applicable?''.
Kind regards,
Johan
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Anonymous replied on Mar. 14, 2011 @ 10:53 GMT
Dear Johan,
thanks again for your comments. It is so refreshing to see your amount of certainties and firm convictions, when everybody I know in the field of quantum gravity (and beyond) is always so cautious and tentative in his/her suggestions, proposals and sometimes even results.
I comment below to some of your comments.
>The problem of quantum gravity is to give a...
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Dear Johan,
thanks again for your comments. It is so refreshing to see your amount of certainties and firm convictions, when everybody I know in the field of quantum gravity (and beyond) is always so cautious and tentative in his/her suggestions, proposals and sometimes even results.
I comment below to some of your comments.
>The problem of quantum gravity is to give a description of nature which is >in principle valid on all scales (this is by no means in contradiction >with renormalization). So your answer that it depends upon the scale or >system is unfortunately not valid.
First, a brief comment: as far as I understand it, the problem of quantum gravity is to give a description of gravity and spacetime that works beyond the scales we have already tested, that goes beyond GR and possibly solves physical issues in that theory like singularities etc. Moreover, it is widely believed and quite likely, that it will still be based on some form of quantum mechanics, possibly modified to deal with a peculiar system like spacetime itself, whence the name. If it is valid at all scales or simply at a new range of scales, after which we have to find an even better theory, we do not know yet. Second, even if we have a theory that formally is valid at all scales, in the sense that the theory itself does not break down, this does not imply that it is the best description of things at all scales. An example would be QCD. On the one hand, formally the theory is valid at any energy scales; on the other hand, one uses a lattice formulation of it at strong coupling, and a continuum formulation at weak coupling; then, still at strong coupling, one has different phases, e.g. the quark-gluon plasma, that require different 'effective' formulations, and similarly at weak coupling it is better to use other effective formulations. Further still, at super-high energies, despite the fact that the theory itself does not break down, we know or at least believe that new degrees of freedom should start play a role, so that QCD is not the whole story, for example quantum gravity effects. So what is the best (formulation of the) theory and what is the best way to describe a certain physical system does depend on the scale and the regime and the phase that one is considering. This is not very controversial, I think. I was simply pointing out that we do not have any reason to expect something different from quantum gravity, plus I was taking this expectation seriously in its more conceptual implications (as I see them, of course) regarding the discrete/continuum nature of space. In particular, I point out that GFT are continuum field theories, whose quanta are discrete 'chunks of space'.
>You seem to take the point of view that the observer(s) are somehow living >in ''meta space'' and that the theory should adapt to the ''glasses'' they >are looking through.
I am not sure what you mean by this, nor where I have written something along these lines. The only time I mentioned 'metaspace' is in giving a label to the manifold on which the GFT field is defined, in order to clarify that this (continuum) manifold does not have itself the interpretation of spacetime. I think I mentioned 'glasses' only in referring to standard results in philosophy of science (Lakatos, Feyerabend, Popper, and many others) showing the extent to which observations and experiments are really much 'theory-laden', and not at all 'neutral' (it is not meant to be a bad thing, by the way).
>Of course, this is what you get when you naively combine quantum mechanics >with general relativity which is what brings me to another point of yours >where you say that you do not understand how these issues make the whole >idea of ''quantum space'' unlikely. As I said, the main problem is how to >define ''local observables'' in a ''canonical way'': there exist very good >(read: almost conclusive) no go arguments against the mere possibility for >even doing this. This issue is intertwined with an observer living inside >or outside the universe and it would take pages to explain it in any >detail. What surprises me however is that you deny that while this is an >open problem for 80 years now (indeed, so long) it most likely implies >that it does not work that way (and indeed, I know it doesn't).
the issue of defining local observables in classical and quantum gravity is a thorny one, and indeed I know of only a few 'solutions' to this problem, all requiring the introduction of matter fields. It is already a difficult task in classical GR, and quantum mechanics (especially in its standard interpretation) makes it even more difficult. And it is so in all approaches to quantum gravity I know (otherwise, of course, we would know at least some solutions to the issues), whether continuum or discrete (it has not to do with discrete space at all, but rather with general covariance, which is a necessary property, I think, of any theory of space taking into account the basic lessons of GR), euclidean or lorentzian, in 3 or 4 or higher dimensions, based on more or less standard quantum field theory or on something more exotic, etc. I am not denying anything, I think. Only, exactly because it is not tied to a specific approach to quantum gravity, but a very general problem, it also does not rule out any specific ways of approaching the construction of the theory, nor the general idea of a 'quantum space', given that this simply means a 'space manifesting some quantum properties' or 'a system that does not look like ordinary continuum classical space but reduces to one in some approximation'. Obviously, I would welcome any clear-cut and complete solution to this issue, but I simply am not aware of any.
>Moreover, I guess you start from space and not space-time right?
no. you could formulate (at least in principle) the 'states' of the GFT system to refer to d-dimensional timelike regions embedded in a d+1 spacetime. The distinction between 'states' and 'processes' is a rather general feature of any (quantum) mechanical theory, while the better understanding of the case in which states are associated to purely spacelike data is simply due to the fact that this is the simplest and most studied case. If even the standard distinction of state and processes is somehow felt to be unsatisfactory, then one can try to adopt, in GFT as in any other (quantum) mechanical theory, a more covariant, history formulation. In any case, what I wanted to say in the essay as well as the general features of GFT, do not depend much on this.
>But even on a much simpler plane, you could insist that strict locality is >a property of nature; this immediately rules out all the exotics you are >willing to consider (so here you have a deep physical reason). The >problems with the kind of models you are considering are legio and most >importantly, they lack physical insight and motivation.
You could insist on locality, yes. And clearly to maintain strict locality at all scales and for all descriptions of the physics of spacetime, classical and quantum, rules out a few alternatives and a few possible features of a quantum space. But 1) there are some reasons to doubt that such local description is really available in all circumstances (e.g. locality is defined in terms of a metric, and thus the very possibility of metric fluctuations or superpositions would imply fluctuations and superpositions in locality, and in turn would require to formulate your theory in a framework in which you do not rely on strict locality); 2) even if locality is somehow incompatible with other properties, this only shows that you have to make choices about the basic principles you implement in your theory; fine; indeed, different approaches to quantum gravity explore the consequences of making different assumptions; up to now, no set of assumptions has been proven to provide a theory free of difficulties, so the exploration and the attempt to solve these difficulties is still ongoing. When we will find one set of assumptions and a consequent framework that succeeds in giving a good account of the physics of quantum space, interesting predictions that are corroborated by experiments, we will all be happy and we will be convinced that we have found at least one good theory of quantum gravity. Until then, it is healthy and sensible to follow different approaches based on different assumptions. Your last statement is rather, how to say, weird, and I prefer not to comment.
>Let me give you a few examples : free QFT on flat space-time is exactly >correct without any doubt.
and also strictly speaking totally unrealistic. It would work exactly only if no interaction at all was present, which is clearly never the case in nature. Obviously, it is a very good approximation of phenomena where interactions are very weak, and indeed it is used in this spirit.
>For example, it almost canonically follows from: (a) locality (b) >causality (c) isotropy and homogeneity of the >vacuum (d) 4 dimensions (e) >cluster decomposition (f) Hilbert space representations of the symmetry >group (g) positive energies (h) statistics. If you think about it for a >while, then you recognize that every single requirement is physically >mandatory for the limit of zero interactions. Therefore, you have to think >about how you are going to build an interacting theory but the latter >should have many foundations in common with the free one.
I agree with everything except the last statement. What the first part shows is only, I think, that whatever more fundamental theory we have, and whatever its foundations are, we should be able to show that it has free field theory as a limit in the approximation of very weak interactions. For example it is clear that no flat space symmetry group (i.e. Poincare) can exist on a generically curved space, even if classical, but one should indeed recover it in the limit of flat space, i.e. no gravity. At the same time, one should not build the global poincare' group in the foundations of the more general theory, where indeed it is replaces by a more local, approximate, version.
>Just as plain Minkowski is the short scale limit of general relativity, >the free theory should be the short scale limit of the interacting one - >so we should have asymptotic freedom and not merely asymptotic safety.
As a general line of thought, it could make sense, but we know that quantum gravity treated as a more or less standard quantum field theory obtained from general relativity, treated as a more or less standard field theory, is simply not asymptotically free. Now (and there are then two possibility, either it is still a more or less conventional field theory and it is asymptotically safe (that's the route followed by the asymptotic safety approach to quantum gravity, and in some interpretation by some lattice gravity approaches), or it is not, at a more fundamental level, a standard field theory at all (or does not come from general relativity strictly), because spacetime is not a continuum anymore, or because the degrees of freedom are not encoded in a metric, etc (this is the line of thought followed by several other approaches). Anyway, I am just saying that even taking your argument for granted, it leaves a lot of room for developing the theory in different directions, in my opinion.
>A first step in that direction would consist in giving interacting quantum >theory itself an Einsteinian (meaning local and fully covariant) >formulation. This is a necessary exercise in order to put both theories on >the same level. You may imagine that the interacting theory will not be >causal, have more exotic statistics and not satisfy the cluster >decomposition, but all this should by dynamical: it should follow from the >physical requirements of covariance, asymptotic freedom, locality + the >conditions on the free theory.
what you seem to be suggesting is what people working on 'algebraic quantum field theory' have been trying to obtain rigorously (apart from the requirement of asymptotic freedom, which I fail to see the necessity of nor the realistic implementation). It can indeed be seen as a necessary first step, and it is without doubt of great interest and value, but there is a rather unanimous consensus (including among researchers working on it) that 1) in itself would not address any of the deeper issues (conceptual or physical) that a complete quantum theory of gravity and spacetime is supposed to address, and 2) at the same time it should indeed represent a good approximation of any more fundamental theory, in some regime. The two things are in no way in contradiction, as far as I can see.
>GFT probably satisfies none of those requirements (including covariance!) >and I haven't seen a good principled analysis nowhere in the literature.
I encourage you to look more carefully at the literature; it may not answer all the question you may have (indeed these models are in many way underdeveloped), but it may give you a better idea of what they are about and what are their motivations and goals. More precisely, let me only say that a) GFT renormalization has just started to be investigated, so we do not know if any given GFT model is renormalizable or not, asymptotically free or safe or whatever; b) the condition of 'free theory' is certainly and trivially satisfied, if you simply mean that the GFT free theory should be reproduced in the limit of the GFT coupling constant going to zero (i.e. what happens in ordinary field theory on fixed spacetime); c) the GFT is local in the sense that it deal directly with local 'chunks' of space, which are the fundamental (interacting) quanta of the theory. Being a theory -of- spacetime and not a theory -on- spacetime, however, the standard notions of locality, causality, short and long distance scale, etc etc, are necessarily to be modified or re-interpreted. This is inevitable, to some extent, and we should be mentally flexible enough, I think, to do it when needed.
>So, what do people do? They go in defense mode. They even start to deny >that the free theory is a physical limit. This of course is utter rubbish, >why in principle should nature not be capable of playing around with the >gravitational constant (or the Planck constant or the speed of light) ? >You may think about c as a definition of a second starting from a meter, G >as a conversion between mass and a meter and hbar as setting the scale for >the meter itself. So again, it appears totally obvious to me that the >limit of zero G in theory space should exist (as well as the limit of zero >interactions) and it is the knowledge of that limit which should be a >foundation of your theory just as special relativity is for general >relativity in the Palatini formalism and just like classical mechanics is >for quantum mechanics in the deformation quantization approach. This is >actually also the case for the thermodynamic limit of absolute zero; there >have been numerous attempts like stochastic vacuum field fluctuations as >an alternative to QED and a big chunk of the physics is determined by the >T = 0 limit. This is something which is fundamentally lacking in all >approaches to quantum gravity (except one) and it is a big mistake.
none of what you wrote above is controversial, nor in any contradiction with the fact that we have to go beyond this limiting case in defining conceptually and mathematically our more fundamental theory of quantum gravity, just as we had to go beyond special relativity, encoding it as a limiting case only, in constructing general relativity. We are trying to do just that, bringing in as much as we can of current theories in building new and more general ones, based necessarily on different assumptions (or at least a reformulation of the same assumptions in a different more general context), but recovering the old assumptions in well controlled approximations.
Different approaches to quantum gravity take different route from known physics towards new, unknown physics, exploring different assumptions and ideas, but I think all agree with the above remarks of yours.
>PS: I do not care about how you write things, expository skills are a >matter of social convention
no, expository skills are important skills, and I care about improving in those as in others
>and I have never cared too much about what others ''think''.
I do care what others think, because I can learn from them, not always, but often
>What I do care about is what you write and as far as I can see, you repeat >all the hopes and ''misconceptions'' I have heard for more than 10 years.
thanks a lot for your criticisms. I encourage you to read more carefully the quantum gravity literature of the last 10 (actually, 80) years, because I think you can find a good deal of interesting ideas and results. On my part, I look forward to read your essay and other published work, hoping for the enlightenment and wisdom that clearly the rest of the quantum gravity researchers and articles could not provide.
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Author Daniele Oriti replied on Mar. 14, 2011 @ 10:57 GMT
Dear Johan,
here are some more comments.
>Now that I see, I did not respond yet to a few points of yours. So, you >admit the notion of a particle becomes superfluous in the context of >relativity: therefore, why are you doing your best to reinstate this >concept in a theory of quantum gravity?!
I am not, if not as an analogy.
>Shouldn't you just do the...
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Dear Johan,
here are some more comments.
>Now that I see, I did not respond yet to a few points of yours. So, you >admit the notion of a particle becomes superfluous in the context of >relativity: therefore, why are you doing your best to reinstate this >concept in a theory of quantum gravity?!
I am not, if not as an analogy.
>Shouldn't you just do the opposite and move even further away (that is >further weaken) from the concept of a particle than it is the case in QFT >on Minkowski?
Indeed. If you look at it carefully, GFTs are conceptually very far away from ordinary QFT, as much as it gets; to start with, they are not even defined on a spacetime.....
>Furthermore you imply that conditions like causality, positive energy and >statistics are background dependent concepts... they are not by any means. >You confuse the principle here with its implementation in QFT on >Minkowski; actually, from the latter we know they are independent issues >even in this weakened context. By this, I mean that, for example, one can >drop positive energies and still get a causal QFT with the right >statistics. If you think about it deeper, you will need a principle for >having an arrow of time (positive energies) and independently you will >need to specify the statistics (that is the very nature of quantum >mechanics). Probably, you would need to specify the spin-statistics >relation (all research to a spin statistics theorem in quantum gravity >points in that direction) as well. So, you still need three independent >principles and you haven't gained anything.
I am not sure I understand what you are trying to say. The notion of causality as such is indeed not necessarily dependent on a background, although we know how to implement it completely only in such case. Still, it can be taken as a definition of a background geometry, but more fundamental than this, as in causal sets or in some formulations of spin foam models. THe notion of energy, on the other hand, is necessarily tied to the existence of a timelike isometry, and thus to a given spacetime, so much that no such notion exist for matter fields on generic geometries or for geometry itself. Statistics refers to the behaviour of the wavefunction
under certain discrete groups, usually coming from the motion group of objects embedded in some fixed space (at least as a topology). I do not deny that they are all important principles in all known physics, nor that some version of these concepts will be useful or even necessary in a more fundamental quantum theory of spacetime dynamics. I do believe, though, that their more fundamental form will be very different than the usual one, which is indeed background dependent, so much so that it is unclear to me to what extent one will still be able to talk about 'causality' or 'energy' as one understands them in standard background dependent, classical physics. I am not sure what the controversy is, here.
>The problem is that you assume a priori that gravity has to be quantized >like any ''particle'' does.
I have never stated anything like this, and I certainly do no assume it.
>You care to give a good physical motivation for this, apart from saying >that ''quantum theory as we know it should be universally applicable?''.
Again, I have never stated this as a matter of principle. In fact, I do believe that a drastic re-interpretation of quantum mechanics, if not a formal modification of it, will be necessary to understand properly the physics of quantum space. This will probably be true, again, even if the mathematical formulation of our quantum gravity models turn out to be formally rather conventional quantum mechanical theories, simply because, beyond their formal aspects, they aim to describe physics 'in absence' of spacetime, exactly because they want to describe the physics 'of' quantum spacetime.
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Anonymous wrote on Feb. 28, 2011 @ 15:18 GMT
Dear Danielle,
While reading your essay , I became very aware that I am not a professional scientist, but I understood very well your point of vieuw, which is very clear as you mention it in the end "IT DEPENDS".
In my simple vieuw it means that what you wrote does not yet give you a clear "yes" or "no" on the question, this of course is very understandable because I think that none of us has a ready, steady go explication of the fundamental questions of our existance and our universe. I even think you are very courageaous to admit that "it depends".
I am enjoying very much every essay in this contest, it means that our minds are looking for explications, the many vieuws distributed are for me like a rainbow , all promising coulours above a dark landscape, very encouraging.
We need the scientists and the cosmologists , the quantum physicians, the historians and the philosophers to make progress in our understanding, the danger however is that anyone who is a specialist forgets to stay in contact with other specialismes.
You mention in your essay singularities, for myself I wonder if these "ideas" are not only existing in our minds,and not in the "material reality" we are living in, what in fact is a point with no dimensions ? The Planck scale , is the ultimate border of our perceptance, the singularities you mention are also part of this area where all measurements are impossible, once accepting that singulairities only exist in our minds they no longer are subject of formula's and so we encounter less infinities, for that I like to mention my own contribution to this wonderfull thought process :
fqxi.org/community/forum/topic/913,
of course I have to admit that the consequences of my thoughts DEPEND on the basic assumptions but if we have no assumptions or beliefs we don't have to prove anything isn't it ?
I wish you also good luck with the contest.
kind regards
Wilhelmus de Wilde
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Anonymous replied on Mar. 5, 2011 @ 18:33 GMT
Dear Wilhelmus,
thanks for your kind comments.
Let me briefly reply on just one point about the intended meaning of my 'it depends'. It is not meant to simply state that ''we will never know for sure'', or that ''we do not know''. I agree with the latter of course, and not so much with the former statement. But it is not what I meant. What I meant is that the answer to the discrete/continuous question for quantum space can be possibly given exactly theoretically, and possibly even tested experimentally (being very speculative), but it will depend on the specific circumstances in which one poses it, in the same sense in which a similar question asked regarding a condensed matter system does. I gave some arguments for this view, offered some speculations, and pointed out that some recent work in quantum gravity has the potential to make the above a bit more precise. The position based on an 'it depends' of a different type, i.e. in which the precise conditions on which 'it depends' are not specified to some extent, would be at risk of being sterile.
Concerning singularities, indeed, several if not all practicing scientists believe the notion of singularity is but a label for a physical situation we do not understand yet, but not something physical in itself. However, the task is then to build up a theory of what happens in such situations, and unfortunately to simply deny their realities is not enough. We all have to be able to do better.
Thanks again and good luck to you as well!
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Peter Jackson wrote on Mar. 2, 2011 @ 17:10 GMT
Danielle
Thank you for a very well written and comprehendable essay, exploring important territory in a clear and innovative way.
This has some interesting parallels with mine, which I hope you will be interested in reading to give you a different and very reality based perspective of the same territory (the string is also rich).
If you are able to increase the number of moving variables our brains can normally deal with I hope you might find it rewarding. I'd be interested in your response.
Very best of luck in the competition.
Peter
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Anonymous wrote on Mar. 5, 2011 @ 18:43 GMT
Hi,
thanks for your kind words. Believe me, I would be indeed very happy if I was able to increase the number of variables my brain can deal with! :)
Best,
Daniele
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James Lee Hoover wrote on Mar. 6, 2011 @ 18:45 GMT
So, is quantum space continuous or discrete? If the above speculation is right, to
realize it concretely will be a revolutionary scientific and cultural experience. But it will not provide us with a better answer to this question than: “It depends”.
Daniele,
I love the above. It is cagey but true. My argument for analogue does not have your authority.
Jim Hoover
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Anonymous replied on Mar. 6, 2011 @ 19:10 GMT
Dear Jim,
thanks a lot for your comment.
I do not know, of course, if I am right or wrong, and only further work will tell. I am sure of one thing only, though, that on this interesting and difficult matter, and at this stage of development, I have no authority whatsoever (as probably nobody else).
Thanks again.
Best,
Daniele
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Johan Noldus replied on Mar. 6, 2011 @ 21:02 GMT
Why do you assume that probably nobody has ''authority'' in this kind of question? Moreover, what would you consider to be a satisfying answer ? If I tell you that local realism cannot be excluded by any experiment, would you say (a) that this is false (b) it is true (c) it is true, but not reasonable? Now suppose I would say that there is no good reason to abandon the continuum and that there exist strong arguments for it such as locality and local Lorentz covariance. Would you say then that (a) this might be true, but it doesn't prove that space-time is continuous since there is an extremely tiny possibility that my assumptions fail (b) this is true and probably means that space-time is a continuum (c) I exaggerate (and you explain why). Moreover, take now into account the ''failure'' of discrete space-time after 30 years and the impossibility of defining local observables for the gravitational field (even in classical gravity), how would you balance these facts?
To make myself crystal clear; suppose you have to bake a chicken and someone would actually make a fire and bake it on a plate, or someone else would put it on a plate and leave it in the sun holding a magnifying glass over it. Would you encourage the second option, knowing the benefits of the first?
Best,
Johan
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Author Daniele Oriti replied on Mar. 14, 2011 @ 11:01 GMT
>Why do you assume that probably nobody has ''authority'' in this kind of >question?
I simply mean that I am full of respect for anyone has studied carefully these issues (philosophical, mathematical, physical), thought hard about them, and understood already some aspects of them, but I am reluctant to grant 'authority' to anyone because 1) it is 'ideas' and 'results' that can have...
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>Why do you assume that probably nobody has ''authority'' in this kind of >question?
I simply mean that I am full of respect for anyone has studied carefully these issues (philosophical, mathematical, physical), thought hard about them, and understood already some aspects of them, but I am reluctant to grant 'authority' to anyone because 1) it is 'ideas' and 'results' that can have authority, not people, in science; 2) the subject is so difficult and our current understanding so incomplete (even if often tantalizing and exciting) that even ideas and results can only be taken as tentative and partial, so have even less 'authority'.
>Moreover, what would you consider to be a satisfying answer ? If I tell >you that local realism cannot be excluded by any experiment, would you say >(a) that this is false (b) it is true (c) it is true, but not reasonable?
if something 'cannot be excluded by any experiment' it is not a scientific fact, but at best a fertile philosophical hypothesis. Fine, follow it and let us see what scientific theory one can construct on its basis, and then how it compares with experiments and with other theories. If you simply mean that no existing experiment contradicts local realism, I would say that this is good, but does not imply that much, as it simply means that it should be reproduced in some approximation.
>Now suppose I would say that there is no good reason to abandon the >continuum and that there exist strong arguments for it such as locality >and local Lorentz covariance. Would you say then that (a) this might be >true, but it doesn't prove that space-time is continuous since there is an >extremely tiny possibility that my assumptions fail (b) this is true and >probably means that space-time is a continuum (c) I exaggerate (and you >explain why). Moreover, take now into account the ''failure'' of discrete >space-time after 30 years and the impossibility of defining local >observables for the gravitational field (even in classical gravity), how >would you balance these facts?
I would say that I do not find the arguments for the continuum as a fundamental description of space so compelling as you seem to do, but also that there are indeed interesting approaches to quantum gravity (e.g. asymptotic safety) based on continuum spacetime and that they should be pursued and developed to see what they teach us. Once we have one or more complete formulations of quantum gravity, we will see what assumption or picture of spacetime was more useful or correct. If by 'failure' you mean that no approach to quantum gravity has proven successful after 30 years, I would point out that 1) this includes both discrete and continuum approaches, so that past 'failures' do not lend support neither to continuum nor to discrete approaches as such; 2) that 'failure' is a misnomer because we have learnt a great deal from all of them (including the one that failed most definitely, i.e. perturbative quantization of gravity around flat space in the continuum), and we are building up on their partial successes as well as on their 'failures'.
>To make myself crystal clear; suppose you have to bake a chicken and >someone would actually make a fire and bake it on a plate, or someone else >would put it on a plate and leave it in the sun holding a magnifying glass >over it. Would you encourage the second option, knowing the benefits of >the first?
Being (I think) a moderately sane person, I would certainly eat happily the baked chicken; I am happy to taste any type of baked chicken recipe (also because I don't think I know what the perfect and correct recipe is, even if there was a single one). Unfortunately, up to now, all those that have come to me with a purported perfectly baked chicken have either misunderstood what a chicken is, and brought all sorts of less palatable animals, or misunderstood what baking and cooking means, and brought a chicken that was still completely raw, or entirely burnt, or with a disgusting sauce, or even still alive and running. So, I keep waiting for those who are trying to bake the proper animal in a proper way, aware of the difficulties in doing so, and willing to do mistakes but not to call a way too early (and thus disappointing) dinner.
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Russell Jurgensen wrote on Mar. 7, 2011 @ 21:08 GMT
Dear Daniele,
I wanted to say hello and let you know how much I enjoyed reading your essay. I appreciated how it gave an understandable context for how a condensed matter system is analyzed starting from what is viewed at a macro level and nicely diving down into the details. I was uncertain if group field theory deals with the nucleus and the strong interaction. I thought your discussion was extremely relevant about what it might take to find a deeper explanation. Thanks for writing a very approachable and interesting essay.
Kind regards, Russell Jurgensen
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Author Daniele Oriti replied on Mar. 13, 2011 @ 16:38 GMT
Dear Russell, thanks for your very kind words. I take the opportunity you offer to comment briefly on whether GFTs do or can account also for nuclear physics, strong interactions and other matter dynamics. The very first thing to keep in mind is that GFTs as such are only recently receiving more attention, so
very few of these issues have been tackled. In particular, at the moment GFTs are studied and explored from the point of view of pure gravity, i.e. interpreted as models for quantum spacetime physics in absence of matter, encoding only the quantum gravitational degrees of freedom. Second, there are two (alternative?) points of view on how matter should be studied in this context. One is that one should add more degrees of freedom, more variables, those encoding matter fields, to the existing models, so to 'couple' matter to gravity, and then study the resulting coupled dynamics of both. In particular, one would then be interested in studying whether quantum gravity effects alter the dynamics of matter in a way that is falsifiable by experiments, or if quantum gravity helps in understanding better puzzling features of matter dynamics. Some models of GFT (and spin foam models) of gravity coupled to matter and gauge fields have been developed, but not much studied in their consequences yet. Another point of view is that matter fields and particles, and possibly also gauge fields, should not be added to the pure spacetime degrees of freedom, and one should not 'complicate' further existing quantum gravity models. Rather, this point of view goes, matter should 'emerge' from quantum spacetime dynamics itself, in some appropriate regime, a bit like excitations of a fluid, behaving indeed as scalar fields, emerge in the hydrodynamic description of it, from the same microscopic degrees of freedom that describe the fluid itself. If this point of view is correct, we should not make existing models more 'complete' or 'complicated, but rather learn first in what regime a description of space as a continuum is possible, and then how to 'extract' or identify, in this regime, the degrees of freedom that correspond to macroscopic gravity and those that correspond to other forces or particles. Needless to say, also this line of thought has been explored to some limited extent only recently, so it is early to say which alternative is more promising or successful. Clearly, how much and what GFTs have to say about the rest of physics, beside spacetime physics, depends a lot on which of these two perspectives one takes, as well as the mathematical and conceptual tools one decides to use similarly depend on this choice. We'll see.
Best,
Daniele
Russell Jurgensen replied on Mar. 14, 2011 @ 19:02 GMT
Dear Daniele, Thank you for your thoughtful reply and the solid approach you take towards analyzing models. I gave it a high rating. I realize there is only one day left, but I hope you will have a chance to read my essay that takes a different perspective to analyze a possible reason for particle energy.
Kind regards, Russell
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T H Ray wrote on Mar. 11, 2011 @ 15:39 GMT
Ciao Daniele,
Nice job! Indeed, one cannot even ponder a structure for space unless time (as in GR) is added. I like the way you get down to the nitty gritty of the topic. I have always admired Fotini Markopoulous's concept of geometrogenesis and I'm glad to see it getting more attention.
Thanks for this, and I hope you get a chance to visit my essay as well.
Best,
Tom
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Author Daniele Oriti replied on Mar. 13, 2011 @ 16:39 GMT
Dear Tom, thanks for your interest and appreciation. I am trying to read as many essays as possible, so I am looking forward to read yours. I am indeed enjoying a lot the melting pot of ideas and perspectives offered by such a variety of contributors. Regarding your mention of the 'geometrogenesis' idea, I find it indeed very fascinating. I find it interesting and fascinating first of all in the terms and context (quantum graphity) in which the name has been first proposed, by Fotini and others, as a (phase) transition from a discrete 'proto-spacetime' discrete structure to another, still discrete structure in which one can however see already some basic spacetime notions as applicable, like locality or dimension. But also, I am attracted by the broader idea of spacetime and geometry as emerging from a sort of phase transition, and possibly involving also a discrete-coninuum transition, from 'something' that cannot be interpreted in spacetime terms. In this broader sense, the idea is of course much older, and has been explored to some extent in other approaches like discrete gravity (Regge calculus, dynamical triangulations, causal sets, etc). Also, a scenario of this type has been considered, even if maybe not explored in too concrete terms, in analog gravity models in condensed matter, as well as put forward in a cosmological context. It is indeed, I think, cool stuff!
ciao
Daniele
Author Philip Gibbs replied on Mar. 16, 2011 @ 08:41 GMT
Daniele, it is good to see you in this contest and doing well. I have admired the group field theory approach since its origins with people such as Boulatov. I mentioned it in my review if discrete space-time concepts back in arXiv:hep-th/9506171. I am pleased that you and your colleagues are keeping the idea alive and continuing to develop it.
As you say geometrogenesis goes back a long way. For example I discussed very similar ideas in arXiv:hep-th/9505089 but did not come up with such a great name or concrete realization. Even earlier forms of similar work are mentioned in my review. Fotini Markopoulous has done a great job of making the concepts much clearer in the context of quantum graphity. It would be be a big development if such phase transitions could be found in relation to a more mathematically rich approach such as group field theory. Do you see any indications of this being possible?
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Author Daniele Oriti replied on Mar. 19, 2011 @ 12:54 GMT
Hi Philip
Thanks a lot for your encouraging comments, and for the useful references. I do have indications that this type of phase transitions can be realized also in complex models like GFTs, although of course they are indirect indications and indications only. One example is that of matrix models for 2d gravity, where exactly something like this happens and which are in both conceptual and mathematical terms the (very successful) precursors of GFTs. We even have very preliminary work in this direction, but it is way to early to say whether our results will hold after further scrutiny and development.
Best,
Daniele
Janko Kokošar wrote on Mar. 12, 2011 @ 06:40 GMT
Dear Daniele Oriti
As generally it bother me at all contestants that Zeilinger-Brukner theory of atomization of information is not mentioned here. Feynman also mentioned similarly as they. So the essence is in discrete world. Almost obvious existence of Planck's space-time shows similarly. It would be well, that all contestants should mentioned this - I think on proponents and opponents of digital physical world. I have not read all essays, does anyone mentioned this?
It is a general argument (also yours) that quantum field theory is continuous, and that field is more important than particles. But we should not ignore that final version of QFT is in discrete Planck's space.
You mentioned richness of those models. But we should be aware that there is also richness of possibility of simple models. It is expected that quantum gravity should be a simple theory. You gave a comparison with condensed matter. This can be also a rich topic, but this is not necessary for foundations of this. And, foundations of condensed matter and quantum gravity are different.
You mentioned that you begin with quantization of space. It should be well to mention that space-time without matter does not exist, so this is a quantization of matter. (But from your graphs it seems, that this is your standpoint.)
You mentioned that wave function exists in a every node. It seem to me, that wave function is only a thing of continuous space. I speculate this after reading Brukner-Zeilinger interpretation (quant-ph/0212084).
I was late for this contest, so my ideas can be read here. http://vixra.org/pdf/1103.0025v1.pdf
I have also an article, which is not speculative and it is a base for the above article. http://vixra.org/pdf/1012.0006v3.pdf There are also additional claims about connections between matter and space-time. I need someone who will be the arxiv endorser for this article. So that I will get opportunity, that my theories will be discussed.
Best regards
Janko Kokosar
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Author Daniele Oriti replied on Mar. 13, 2011 @ 16:41 GMT
Dear Janko,
Thanks for your interest and comments. I reply to some of them below.
>As generally it bother me at all contestants that Zeilinger-Brukner theory
>of atomization of information is not mentioned here. Feynman also
>mentioned similarly as they. So the essence is in discrete world. Almost >obvious existence of Planck's space-time shows similarly....
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Dear Janko,
Thanks for your interest and comments. I reply to some of them below.
>As generally it bother me at all contestants that Zeilinger-Brukner theory
>of atomization of information is not mentioned here. Feynman also
>mentioned similarly as they. So the essence is in discrete world. Almost >obvious existence of Planck's space-time shows similarly. It would be
>well, that all contestants should mentioned this - I think on proponents
>and opponents of digital physical world. I have not read all essays, does
>anyone mentioned this?
I, for one, have not mentioned this theory because I do not know much about it. I take your comment as a suggestion for learning more about it. Thanks.
>It is a general argument (also yours) that quantum field theory is >continuous, and that field is more important than particles.
well, in a sense you are right. But indeed, this is what current quantum field theory seems to teach us. And I think we have to first of all take seriously what we currently know about the universe, before moving beyond it. But indeed, one needs to be careful in the assumptions made, and flexible enough to question any current wisdom.
> But we should not ignore that final version of QFT is in discrete Planck's >space.
I am not sure what you mean by this. We do not know at present, if space at the Planck scale is (best described as) discrete or continuous. We are entitled to make our favorite assumptions and see where they lead us, but we simply do not know. Indeed, my essay tried to paint a picture of quantum space that is more complex than this.
>You mentioned richness of those models. But we should be aware that there
>is also richness of possibility of simple models.
I fully agree with this. What I wanted to stress is that the set of possible 'phases' and regimes of the physical system corresponding to quantum space can be very diverse, so to make the answer to the question whether space is discrete or continuous not univocal. I do not know if this richness is to be encoded in 'complicated' mathematical models, or can be reproduced on the basis of simple ones. Only further research can tell us.
>It is expected that quantum gravity should be a simple theory.
By whom? opinions about this, as far as I know, are various. In any case,
>You gave a comparison with condensed matter. This can be also a rich
>topic, but this is not necessary for foundations of this. And, foundations
>of condensed matter and quantum gravity are different.
I suggested a point of view on quantum space based on what we know from (or at least from how I interpret) recent results in quantum gravity research; this point of view is inspired by the 'analogy' with condensed matter. Nothing more than this.
>You mentioned that you begin with quantization of space. It should be well
>to mention that space-time without matter does not exist, so this is a >quantization of matter. (But from your graphs it seems, that this is your >standpoint.)
The possibility of giving physical meaning to spacetime without matter is indeed questionable and questioned in both philosophy and physics. However, vacuum spacetimes can and are studied in General Relativity, so they make sense at least in some approximation. On whether and how matter should be incorporated in or shown to emerge from this description of quantum space, see my reply to another comment above.
>You mentioned that wave function exists in a every node. It seem to me,
>that wave function is only a thing of continuous space. I speculate this >after reading Brukner-Zeilinger interpretation (quant-ph/0212084).
In the models I considered, GFTs, indeed one can define an compute wave functions associated to discrete chunks of quantum space, individual nodes of graphs. So this definition at least does not need a continuous space, in a physical sense.
>I was late for this contest, so my ideas can be read here. http://>vixra.org/pdf/1103.0025v1.pdf
>I have also an article, which is not speculative and it is a base for the >above article. http://vixra.org/pdf/1012.0006v3.pdf There are also
>additional claims about connections between matter and space-time. I need >someone who will be the arxiv endorser for this article. So that I will
>get opportunity, that my theories will be discussed.
As I am trying to read as many essay as possible, I, of course, try to read as much available literature as possible on this topic. So, thanks a lot for your suggestion.
Best,
Daniele
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Ray ASCHHEIM wrote on Mar. 13, 2011 @ 21:52 GMT
Dear Daniele,
I really appreciated your essay which bring very interesting and innovative ideas while still being of perfectly scientific level. I share your view of the cosmological phase transition instead of a big bang. My own work totally agree with that thesis. Quantum space is now crystallized (as an hyperdiamond) and should have emerged from a liquid or gaseous phase. It is made of a trivalent graph, evolving through pachner moves, and quantized as spin foam. The crystallographic structure embed standard model through e8 roots.
Best regards
Ray
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Anonymous replied on Mar. 13, 2011 @ 22:59 GMT
Hi,
thanks a lot. I am happy to see that similar ideas are shared by people coming from different paths. It can still be we are all wrong, of course, but at least it serves as an encouragement to keep working.
Best,
Daniele
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Anonymous wrote on Mar. 14, 2011 @ 14:14 GMT
Dear Daniele,
As a first comment, you seem to confuse my certainty about what does not work with the attitude that I know how it works. Maybe even this last statement is true, but that remains to be seen; in contrast to you, I am not justifying my own shortcomings by relating them to the weaknesses of others.
In the first paragraph you say nothing I disagree with, the point I...
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Dear Daniele,
As a first comment, you seem to confuse my certainty about what does not work with the attitude that I know how it works. Maybe even this last statement is true, but that remains to be seen; in contrast to you, I am not justifying my own shortcomings by relating them to the weaknesses of others.
In the first paragraph you say nothing I disagree with, the point I made was that it has nothing to do with the question of the contest whatsoever which obviously seems to be : ''if we have a theory valid at all scales, does its prescription require a continuum or not? Is it a theory in which space-time is actually measured or not?''. If it were just a matter to simply push the theory to some higher energy scale, we could as well be pleased with perturbative quantum gravity.
What I mentioned with the observers in ''meta space'' simply was that if you take space-time as quantum, the theory is not closed; an observer would have to measure things from the outside which brings along many difficulties which you might want to think about deeper.
Concerning local observables; yes in GR and standard approaches, this is a problem of general covariance which is usually circumvented by breaking it through adding point matter (which is of course the wrong thing to do). However, even at this level, you need to be careful what you mean: do you think about quantum covariance or classical covariance (even within quantum gravity)? Anyhow, this problem simply means that you are asking the wrong questions; there are no physical observables in vacuum gravity (even at the classical level). One cannot claim really that the Dirac observables are so. This means that you never measure geometry and that is in my opinion the correct interpretation of classical relativity where you could get local observables from studying relationships between planets expressed in their physical eigentimes. My ideas concerning this still go a few steps further and really avoid the problem too in the quantum theory.
Concerning my insisting on the free theory, you do not comprehend what I say. Obviously, the free theory is unrealistic just like absolute zero is in thermodynamics (that is actually a law). However, this does not preclude that this theory should exist as a limit of your theory and actually even more, that it might serve as a basis for your theory. I gave you the example of stochastic electrodynamics where the stochastic background field is exactly the defining property of the thermodynamic limit T=0. The whole physics at T > 0 is crucially influenced by this feature in the sense for example that the orbit of a classical point like electron around a nucleus can be computed to be stable and that in the case of hydrogen, the probability distribution of the corresponding ground state actually coincides with the predictions of non-relativistic quantum mechanics. Another example like that is how we build QFT and compute cross sections. You may not like this, but there are deep physical reasons for why a theory is build like this. And of course, I was not thinking about the GLOBAL Poincare group like string theorists do, but about LOCAL Poincare groups, something which you could have learned by now by reading my little work.
Concerning the asymptotic freedom, it is just not an ''argument'' but a deep realization how to bypass Haag's theorem and how GUT's in general behave. Actually, classical gravity is also asymptotically safe by means of the equivalence principle. And no, if you combine asymptotic freedom with strict locality, all the exotic possibilities you imagine do not exist anymore. So your freedom of ideas is an illusion.
AQFT is just a reformulation of the same theory in a different mathematical language, so it is not very pleasing. What I say is that standard QFT is even wrong at the level of interactions and free theories in curved space-time. This requires a different theory and not some mathematical masturbation of the old one.
Btw, I do know the literature quite well and nothing what you say has anything to do with a principled analysis which means : formulate physical principles and study its mathematical representations.
Again, concerning the free theory; what you say is rather misplaced. GR did not start from special relativity, it actually required new math and a physical principle why special relativity would hold locally. Nothing of that sort is done in GFT as far as I see, where the rules are heuristic and derived from some approaches resulting from QM + GR.
By the way, nothing published in the last 10 years comes even close to answering the issues I adressed.
Kind regards,
Johan
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Author Daniele Oriti replied on Mar. 14, 2011 @ 16:16 GMT
>As a first comment, you seem to confuse my certainty about what does not >work with the attitude that I know how it works. Maybe even this last
even this type of certainty is something I quite envy. I am not certain even about the incorrectness of any of the many approaches to quantum gravity I know of. Obviously, I have my own preferences, which I try to base as much as I can on...
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>As a first comment, you seem to confuse my certainty about what does not >work with the attitude that I know how it works. Maybe even this last
even this type of certainty is something I quite envy. I am not certain even about the incorrectness of any of the many approaches to quantum gravity I know of. Obviously, I have my own preferences, which I try to base as much as I can on careful reasoning, and I am forced, as a professional working in this area, to place my bets on what I feel has the best chances of working.
>statement is true, but that remains to be seen; in contrast to you, I am >not justifying my own shortcomings by relating them to the weaknesses of >others.
that's rather gratuitous. anyway, it does not alter much the content of the discussion, so I do not need to comment further.
>In the first paragraph you say nothing I disagree with, the point I made >was that it has nothing to do with the question of the contest whatsoever >which obviously seems to be : ''if we have a theory valid at all scales, >does its prescription require a continuum or not? Is it a theory in which >space-time is actually measured or not?''. If it were just a matter to >simply push the theory to some higher energy scale, we could as well be >pleased with perturbative quantum gravity.
good we agree on what I wrote. My point was that even if a theory is valid in principle at all scales, for example a theory of spacetime, this does not mean that it is 'ultimate' or 'most fundamental' nor that it would give a univocal answer to the discrete/continuum question for spacetime. GFT could well be in principle valid at all scales, but, I argue, admits or would admit a variety of descriptions for spacetime at different scales and in different phases. At a more established and mundane level (and maybe less directly relevant to the spacetime issue), QCD is valid at all scales but its prescription requires a discrete spacetime in the non-perturbative regime, and a continuum one at weak coupling, to be useful in any way.
>What I mentioned with the observers in ''meta space'' simply was that if >you take space-time as quantum, the theory is not closed; an observer >would have to measure things from the outside which brings along many >difficulties which you might want to think about deeper.
on this:
1) I am not arguing for the treatment of spacetime as a whole (the universe) as a quantum system (more than, possibly, at some very coarse level of approximation), somehow to be measured from the outside in the standard interpretation of quantum mechanics. Indeed, this is physically highly dubious. And in fact, one thing I find attractive in GFT (and other approaches) is that it allows you to consider 'local' chunks of spacetime, and to ask question about what an outside observer would measure at the boundary of such regions. It is still true, of course, that we are far from being able to reconstruct a continuum space (as we should at least in some limit) from this description and to check if it gives reasonable physics. I do not think I claimed the opposite.
2) I am aware of (and I stated) the difficulties in applying quantum mechanics as we know it to spacetime, as I am aware of the difficulties in developing suitable modifications (whether mathematical or interpretational) of it that would make application to spacetime easier.
I do agree that there is also a logical possibility that one should not apply any form of quantum mechanics at all to spacetime, but rather leave it classical or try to define it altogether from the interactions of (quantum) matter fields or similar (e.g. strings), without treating it as a physical system in itself that exist outside matter. In fact, I am interested in any approach that tries to do so, either philosophically or physically. However, I have not seen yet any satisfactory theory constructed on this basis, and on the other hand I am more convinced by the logical alternatives.
>Concerning local observables; yes in GR and standard approaches, this is a >problem of general covariance which is usually circumvented by breaking it >through adding point matter (which is of course the wrong thing to do).
the inclusion of (not necessarily point-like) matter does not break any covariance. And it does not sound wrong, given that we do observe matter around us.
>However, even at this level, you need to be careful what you mean: do you >think about quantum covariance or classical covariance (even within >quantum gravity)? Anyhow, this problem simply means that you are asking >the wrong questions; there are no physical observables in vacuum gravity >(even at the classical level). One cannot claim really that the Dirac >observables are so. This means that you never measure geometry and that is >in my opinion the correct interpretation of classical relativity where you >could get local observables from studying relationships between planets >expressed in their physical eigentimes. My ideas concerning this still go >a few steps further and really avoid the problem too in the quantum >theory.
It is well possible that the consideration of vacuum space is but a idealization, and I agree that the inclusion of matter is necessary in any model of (classical and quantum) gravity to extract physical result. See the answer I gave above to another contributor. I have no problem with this. I do not agree on the implication that the consideration of vacuum space and gravity is wrong even as an idealization, and necessarily leads to the use of the wrong mathematical or conceptual structures. But again, I think everybody would welcome any solid advance whatever point of view it is based on.
>Concerning my insisting on the free theory, you do not comprehend what I >say. Obviously, the free theory is unrealistic just like absolute zero is >in thermodynamics (that is actually a law). However, this does not >preclude that this theory should exist as a limit of your theory and >actually even more, that it might serve as a basis for your theory. I gave >you the example of stochastic electrodynamics where the stochastic >background field is exactly the defining property of the thermodynamic >limit T=0. The whole physics at T > 0 is crucially influenced by this >feature in the sense for example that the orbit of a classical point like >electron around a nucleus can be computed to be stable and that in the >case of hydrogen, the probability distribution of the corresponding ground >state actually coincides with the predictions of non-relativistic quantum >mechanics. Another example like that is how we build QFT and compute cross >sections. You may not like this, but there are deep physical reasons for >why a theory is build like this.
I have no problem with any of the above, but I do not see how it changes the point of the discussion. The fact that a theory exists as a limit of another does not imply (although in some cases it is true) that the other should be built on the same conceptual or physical foundations.
An example is any quantum theory, which has some classical theory as a limit, but is built on entirely different conceptual foundations. Some new features may also arise (and even be taken as foundational) in the weak coupling limit of a more general theory not based on them. Unless you simply mean that well tested, if approximate theories, should be reproduced necessarily as a consistency check on newer ones. With this, I obviously agree.
>And of course, I was not thinking about the GLOBAL Poincare group like >string theorists do, but about LOCAL Poincare groups, something which you >could have learned by now by reading my little work.
I did not have time to read it, indeed. I look forward to do so. Let me note that even the local Poincare' group could be a feature that arise only in some approximation (e.g. if anything like 'deformed special relativity' is true in some semi-classical regime), and it is not obvious to me that it should be taken as a foundational principle.
>Concerning the asymptotic freedom, it is just not an ''argument'' but a >deep realization how to bypass Haag's theorem and how GUT's in general >behave. Actually, classical gravity is also asymptotically safe by means >of the equivalence principle.
I guess you mean 'asymptotically free' here. Although I do not understand your application of the terms to a classical theory, given that I know of their definition and application only to quantum field theories. I'll check again the literature.
>And no, if you combine asymptotic freedom with strict locality, all the >exotic possibilities you imagine do not exist anymore. So your freedom of >ideas is an illusion.
Once more, even if what you say was true, it would merely imply the incompatibility of assuming asymptotic freedom and strict locality, with assuming other basic principles or structures. Ok. Useful. But it would not say much, I think, on the validity of one over the others, which would have to be decided on other grounds (e.g. mathematical first and experimental then). In order to do so, I think it is important to encourage freedom of ideas and the possibility to pursue even mutually incompatible ones, until one acquires more weight that others. I do not think we are there yet.
>AQFT is just a reformulation of the same theory in a different >mathematical language, so it is not very pleasing. What I say is that >standard QFT is even wrong at the level of interactions and free theories >in curved space-time. This requires a different theory and not some >mathematical masturbation of the old one.
Fine. So we need a new theory of gravity, because GR admits vacuum solutions and dynamics, which cannot be truly physical, and new theories of matter, because the ones we have are based on interacting quantum field theories, which are also wrong. Still, we need to recover them in some approximation, since they have proven useful and physically correct to some extent. This seems to leave us with quite a task. But I still do not understand your proposal. It should be quite something, though, given the task, so I look forward to read your essay.
>Btw, I do know the literature quite well and nothing what you say has >anything to do with a principled analysis which means : formulate physical >principles and study its mathematical representations.
Physics, for what I see, does not always work in such simple way, unfortunately, and sometimes we have to work in a much more tentative way, until we discover or realize what the correct 'principle' formulation of our theory should be. Actually, I do not think that any theory has been ever developed in such 'principled' way, even though it could maybe be presented this way -after- it has been fully developed. Not even relativity was found this way, and nobody has ever been so clear in his logical thinking than Einstein...
>Again, concerning the free theory; what you say is rather misplaced. GR >did not start from special relativity, it actually required new math and a >physical principle why special relativity would hold locally. Nothing of >that sort is done in GFT as far as I see, where the rules are heuristic >and derived from some approaches resulting from QM + GR.
It is true that we do not have a principle-based formulation of GFT, and that we should try to understand better what its basic principles are or should be, also to guide any future development. If this is what you mean... but so what? Unfortunately, to identify some principles one can trust and simply follow them is not the rule of the game. I wish it was so simple!
>By the way, nothing published in the last 10 years comes even close to >answering the issues I adressed.
I am somehow happy that I am not the only one to disappoint your expectations. And if you really -address- all those issues, univocally, solidly and satisfactorily, well, I am sure your work will be welcomed by the community, so keep up with the work!
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Anonymous wrote on Mar. 14, 2011 @ 14:33 GMT
Dear Daniele,
To respond to your second mail, yes you do reinstate ''particles'' by considering discrete chunks of ''space-time''. Concerning causality, you indeed do not understand what I say. Even in quantum field theories on a background space-time you have two different notions. First you have the light-cones which give you a distinction between what we call future and past (as well as the conformal scale) and second you have the Heisenberg commutation relations. One question is whether these two notions should coincide even for interacting quantum theories on Minkowski. But that was not my point. Nobody knows what causality means in the context of quantum gravity (even not Rafael Sorkin) and the point I made was that it should not be a fundamental principle here. This means that you have to modify somehow quantum mechanics itself unless you want to break local Lorentz covariance.
Second, the notion of energy is indeed thight to timelike isometries in the conventional way of thinking. That is why the conventional way of thinking is wrong (and again you will find an answer to this in my little paper). Third statistics has nothing to do with the wave function, it is a the heart of quantum theory itself; it actually determines the dynamics ! Even more than this, the statistics question is only well posed on Minkowski because swapping free particles there is physically a well defined and path independent operation. The question itself even doesn't make any sense in a curved space-time (even one with a killing symmetry). So what I say is that QFT is even wrong in these cases. The controversy here is that all these principles are the corner stones of quantum theory itself and your favorite approaches leave quantum mechanics itself virtually untouched. That cannot be if you imagine the substitute principles to be very different.
Kind regards,
Johan
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Author Daniele Oriti replied on Mar. 14, 2011 @ 16:35 GMT
>To respond to your second mail, yes you do reinstate ''particles'' by >considering discrete chunks of ''space-time''.
as an analogy, indeed. But as such it does not contradict anything we know about existence or non-existence, validity or not validity of the particle concept, in flat or curved spaces etc.
>Nobody knows what causality means in the context of quantum gravity...
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>To respond to your second mail, yes you do reinstate ''particles'' by >considering discrete chunks of ''space-time''.
as an analogy, indeed. But as such it does not contradict anything we know about existence or non-existence, validity or not validity of the particle concept, in flat or curved spaces etc.
>Nobody knows what causality means in the context of quantum gravity (even >not Rafael Sorkin) and the point I made was that it should not be a >fundamental principle here. This means that you have to modify somehow >quantum mechanics itself unless you want to break local Lorentz >covariance.
I agree that the notion of causality is dubious in a quantum gravity context, and in fact I think I have stated this at some point in this discussion. I also think that locality as well is of difficult application in a quantum gravity context, and not obviously to be used as a foundational principle. In particular, in any framework in which spacetime is somehow emergent or the metric fluctuates, then it is almost necessary that locality should be at least re-interpreted very differently. Alternatively, one can decide to stick to the usual notion of locality and therefore do not follow any approach that necessarily leads to revising it or dropping it. Fine. I am simply not convinced we have such a solid argument for preferring this line of thought. Moreover, let me briefly point out that 'breaking of lorentz covariance' is not the only option, as in some approaches one tries to implement a deformation of the same, still based on 10-dimensional symmetries, only represented by quantum groups rather than lie algebras.
>Second, the notion of energy is indeed thight to timelike isometries in >the conventional way of thinking. That is why the conventional way of >thinking is wrong (and again you will find an answer to this in my little >paper). Third statistics has nothing to do with the wave function, it is a >the heart of quantum theory itself; it actually determines the dynamics ! >Even more than this, the statistics question is only well posed on >Minkowski because swapping free particles there is physically a well >defined and path independent operation. The question itself even doesn't >make any sense in a curved space-time (even one with a killing symmetry). >So what I say is that QFT is even wrong in these cases. The controversy >here is that all these principles are the corner stones of quantum theory >itself and your favorite approaches leave quantum mechanics itself >virtually untouched. That cannot be if you imagine the substitute >principles to be very different.
Beside the fact that I do not agree with some of your statements above, this is not so important. If your point is simply that standard quantum mechanics is based on several assumptions and mathematical ingredients that in turn rest on the existence of a (usually flat) background spacetime, I agree with this. If you infer from this that we will need at the very least a drastic re-interpretation of quantum mechanics in a quantum gravity context, I also agree. Unfortunately, this does not say much about how we should modify it nor implies that much about how or to what extent we can rely on it in developing new theories of spacetime or whatever substitutes it at a more fundamental level. We should work a bit harder, try applying some elements of it, or developing new formulations of it, and see what we get. The approaches I work with are quite flexible as to what formulation or interpretation of quantum mechanics is best suited to them, and will in any case force us a drastic re-interpretation of it, if only because, as I stressed, they are not based on any spacetime in their definition.
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Anonymous wrote on Mar. 14, 2011 @ 15:34 GMT
Dear Daniele,
I start to doubt whether you understand the basics of science. No idea can be proven wrong, a concrete realization can but the principle itself not. The whole scientific enterprise consists of the delicate art of balancing between principles, representations, ontology and experiment. For example, in case of Bell's theorem, most people would say it excludes local realism assuming the experiments favor quantum predictions but this is manifestly false, strictly speaking. Morally, however, I think it is true; by this I mean that a local realist theory matching nature would not be very natural and complicated.
Furthermore, you do not seem to realize the depth of locality and local poincare invariance as fundamental principles of nature (which leads to the continuum). Both are tied to the definition of the vacuum state, something your favorite approaches fail in.
Third, no, by failure I meant failure of discrete approaches. We are actually almost nowhere yet. Nobody knows how to properly construct a smooth effective geometry from a discrete spaghetti, nobody knows even to define the equivalent of a d'Alembertian on random discrete structures and so on... These are merely questions one should try to understand on the kinematical level first and all these difficulties are not present in the continuum approach. I guess you haven't thought too much about these things.
About chickens, there exist plenty of possibilities: either you don't understand what the animal is, or you have prejudices about what it should be. Or perhaps, your palet is not as refined as one would expect it to be from an italian. Anyway, if you do not go and look for the chicken itself and keep on waiting, chances are high you will eat an earthworm in the end.
Kind regards,
Johan
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Author Daniele Oriti replied on Mar. 14, 2011 @ 16:49 GMT
>I start to doubt whether you understand the basics of science.
I see you are not able to avoid personal statements. That is bad. But I think I can still manage to do so, which is good because they are not very useful.
>No idea can be proven wrong, a concrete realization can but the principle >itself not. The whole scientific enterprise consists of the delicate art >of balancing between principles, representations, ontology and experiment.
Thanks for this brief summary of the last centuries of philosophical thinking.
>Furthermore, you do not seem to realize the depth of locality and local >poincare invariance as fundamental principles of nature (which leads to >the continuum). Both are tied to the definition of the vacuum state, >something your favorite approaches fail in.
it could well be that I fail to appreciate fully these principles. However, I have been working also on identifying the basic symmetries and the correct notion of locality that applies, in absence of a background spacetime, to the kind of models I like, and how these characterize the GFT (perturbative) vacuum state. It must mean that I somehow sense, in all my limitations, the importance of them, for any physical theory.
>Third, no, by failure I meant failure of discrete approaches. We are >actually almost nowhere yet. Nobody knows how to properly construct a >smooth effective geometry from a discrete spaghetti, nobody knows even to >define the equivalent of a d'Alembertian on random discrete structures and >so on... These are merely questions one should try to understand on the >kinematical level first and all these difficulties are not present in the >continuum approach. I guess you haven't thought too much about these >things.
Beside once more irrelevant personal statements, I guess I disagree on the evaluation of what we have achieved and understood, up to now, in the different continuum and discrete approaches to quantum gravity. Never mind. There are plenty of clever people I disagree with and others I agree with.
>About chickens, there exist plenty of possibilities: either you don't >understand what the animal is, or you have prejudices about what it should >be. Or perhaps, your palet is not as refined as one would expect it to be >from an italian. Anyway, if you do not go and look for the chicken itself >and keep on waiting, chances are high you will eat an earthworm in the >end.
I agree with all of the above, if you meant it as a general statement; I still fail to appreciate it, if you intended it as referring to me personally.
Now, please excuse me....I have a chicken in the oven....
Member Moshe Rozali wrote on Mar. 14, 2011 @ 19:08 GMT
Hi Daniele. I used the opportunity of this essay competition to write what I feel is the burden of proof for all condensed matter models where Lorentz invariance is emergent, which are presumably rich enough to include the standard model matter content. If you are interested it is here
http://www.fqxi.org/community/forum/topic/856
I am curious about your thoughts, either in the context of your model, or in general.
Best,
Moshe
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Author Daniele Oriti replied on Mar. 14, 2011 @ 19:45 GMT
Hi Moshe,
thanks for your message and interest. I had already downloaded your essay, of course, but I didn't manage to read it yet. I hope t be able to do it by tomorrow.
If I have anything interesting to say, I'll send you my comments.
Best,
Daniele
Member Moshe Rozali replied on Mar. 14, 2011 @ 19:51 GMT
Thanks Daniele. Feel free to send me an email, even after tomorrow.
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Author Daniele Oriti replied on Mar. 15, 2011 @ 11:02 GMT
Hi Moshe,
I managed to read your essay and liked it a lot. I won't manage to write you an appropriate reply to the various issues you raise now, but I'll try to do it (either here or in private) as soon as possible. There are several points I would like to make on them, some partial answers and some more confusion to share, but it takes some time. At least, I managed to vote for your essay!
Thanks again.
Daniele
Moshe replied on Mar. 15, 2011 @ 14:46 GMT
Thanks Daniele. I am not sure for how long I'd check things here, so private email would be best. As I said, I am curious to hear your perspective on these issues.
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Anonymous wrote on Mar. 15, 2011 @ 00:48 GMT
Dear Daniele,
Regarding your first reply, you still seem to deny my statement that what you say is not relevant as an answer to the contest; I do not see why you don't because many people I know do understand so.
Concerning your classical boundaries in a ''partially quantum universe'', I do not see any logical reasoning behind it apart from the desire to have classical boundary structures in order to define observables. For example, how large are these chunks, what physical principle decides upon that ? Moreover, for ordinary particle theory in curved spacetime, no such boundaries are present (and would destroy the coherence of the theory) except at asymptotic infinity which is held flat or de Sitter.
Third, the inclusion of matter needs to break general covariance in one of the following senses:
(a) either you have a diffeomorphism invariant dynamics (that is a new constraint algebra containing the matter variables) but you have to resort to partial observables.
(b) the quantization of gravity with matter will induce anomalies in the algebra.
Concerning the constraint algebra, this question has not even been settled in pure gravity theory because the quantization procedure treats the Hamiltonian different from the spacelike diffeomorphism constraints. Concerning (a), this is physically nonsensical because I do not see how you would retrieve an arrow of time in this way.
Fourth, I did not say that pure gravity was ill defined, I simply said it has no observables; it is an empty theory from the physical point of view, while the limit of zero gravity is not and that is actually the correct vacuum.
Fifth, I do not know of any standard approach to quantum theory which is not grounded in a classical theory. The path integral approach has the classical action as starting point and likewise so for the Hamiltonian one. The only kind of reasoning which departs from quantum concepts partially (but not fully) can be found in the book of Weinberg.
Asymptotic freedom is just the physical idea that on short distance scales the theory becomes a free one. This is a well defined concept in a quantum as well as classical setting.
Finally, relativity was found by reasoning in terms of a new principle. Einstein clearly thought about general covariance and there exist plenty of historical documents to prove that. I am not sure about the person, but I remember he told to Planck about a generally covariant law for gravitation and the response was that nobody would be interested in that.
Moreover, you completely miss the point that finding principles is very difficult because it implies that your really know what you are doing physically.
Kind regards,
Johan
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Anonymous replied on Mar. 15, 2011 @ 15:11 GMT
>Concerning your classical boundaries in a ''partially quantum universe'', I do not see any logical reasoning behind it apart
>from the desire to have classical boundary structures in order to define observables. For example, how large are these chunks,
>what physical principle decides upon that ? Moreover, for ordinary particle theory in curved spacetime, no such...
view entire post
>Concerning your classical boundaries in a ''partially quantum universe'', I do not see any logical reasoning behind it apart
>from the desire to have classical boundary structures in order to define observables. For example, how large are these chunks,
>what physical principle decides upon that ? Moreover, for ordinary particle theory in curved spacetime, no such boundaries are
>present (and would destroy the coherence of the theory) except at asymptotic infinity which is held flat or de Sitter.
I have never mentioned classical boundaries, nor partially quantum universes, whatever that means. I wrote that the formalism allows to consider finite open regions of 'spacetime', with their boundary (quantum) geometry and topology fixed, and bulk geometry and topology fluctuating and dynamical. Indeed, a better understanding of classical and quantum field theories in such generalized context is needed, together with the corresponding possible generalization of standard quantum mechanics. Such generalization, however difficult, seems interesting, if not necessary, to me also beyond this specific approach.
>Third, the inclusion of matter needs to break general covariance in one of the following senses:
>(a) either you have a diffeomorphism invariant dynamics (that is a new constraint algebra containing the matter variables) but
>you have to resort to partial observables.
> (b) the quantization of gravity with matter will induce anomalies in the algebra.
>Concerning the constraint algebra, this question has not even been settled in pure gravity theory because the quantization
>procedure treats the Hamiltonian different from the spacelike diffeomorphism constraints. Concerning (a), this is physically
>nonsensical because I do not see how you would retrieve an arrow of time in this way.
none of the above is correct, in my understanding. The use of partial observables is a more convenient way to deal with Dirac observables, and to understand their meaning as correlations of measured (but not diffeo invariant) quantities. It does not imply any lowering of standards with respect to covariance. One can produce explicit quantizations of the constraint algebra of gravity plus matter which are free of anomalies, and the real question is whether the corresponding quantization has the correct classical limit and produces the correct physics. But there is no obstacle of principle.
>Fourth, I did not say that pure gravity was ill defined, I simply said it has no observables; it is an empty theory from the
>physical point of view, while the limit of zero gravity is not and that is actually the correct vacuum.
I did not question the fact that pure (classical and quantum) gravity is non-physical, because we lack local observables, although I would not be so clear-cut; and in fact I said that this gives one more reason, beside the obvious physical motivation, to introduce matter. I wrote that just as in classical GR pure gravity does represent an idealized case from which we learn things, the same could be true in the quantum case. The limit of zero gravity is physical provided you are not interested in gravity (classical or quantum), which is a shame. As soon as you want to say something about gravity, this limit becomes at best an approximation, as one does in any interacting field theory, and all the problems re-appear and have to be dealt with.
>Fifth, I do not know of any standard approach to quantum theory which is not grounded in a classical theory. The path integral
>approach has the classical action as starting point and likewise so for the Hamiltonian one. The only kind of reasoning which
>departs from quantum concepts partially (but not fully) can be found in the book of Weinberg.
sure. and in fact -any- approach to quantum gravity I know of (including GFT) rests to some extent, in motivation, type of structures used, basic principles that one tries to carry over to the quantum theory, etc on classical GR. again, I never stated that one should somehow invent a quantum theory of gravity and/or spacetime without ever considering GR. so what?
>Asymptotic freedom is just the physical idea that on short distance scales the theory becomes a free one. This is a well defined
>concept in a quantum as well as classical setting.
in my understanding the concept makes real sense only in a quantum theory in which coupling constants run with scales, otherwise you are using the term in a rather non-standard way. Then, QCD is asymptotically free while QED is not, and none of the two is 'asymptotically free' at the classical level, given that there the coupling constants are whatever one sets them to be. In any case, Gravity, treated as a standard quantum field theory, is not asymptotically free, although it could be asymptotically safe. This is true, of course, unless you treat it as a non-standard quantum field theory or you intend the terminology in a non-standrad way. Fine, but you should then clarify what you mean, and then one can check whether what you mean makes sense or not.
>Finally, relativity was found by reasoning in terms of a new principle. Einstein clearly thought about general covariance and
>there exist plenty of historical documents to prove that. I am not sure about the person, but I remember he told to Planck about
>a generally covariant law for gravitation and the response was that nobody would be interested in that.
>Moreover, you completely miss the point that finding principles is very difficult because it implies that your really know what
>you are doing physically.
when I read the historical texts or the original sequence of articles leading to GR, I see a much more complicated story, in which he arrived at the right principles only after a complicated sequence of trial and errors, partial results, later-to-be-discovered inconsistent foundations, glimpses of ideas, and even including formulations of the theory that were based on the very contradiction of the principle of general covariance. He did not first identify the principles and then deduced the results. Theoretical physics does not work like that, I think, unless principles are treated as working hypothesis, but then of course one should maintain a certain flexibility about them. This is exactly because identifying the right principles is difficult (again, I have never stated the contrary), and it is not even something that can be recognized as unique, if not much after the complete theory has been found. As a consequence, I do not feel I can blame any current approach to quantum gravity (a still incomplete theory, yet to be found, really) because it does not start from unique principles, or on already clear ones. Obviously, I also feel it is important to try to clarify the basic assumptions (''principles'') on which they are based, because indeed it may facilitate their development.
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Anonymous wrote on Mar. 15, 2011 @ 01:03 GMT
Dear Daniele,
Concerning your second mail, I will only mention the points I think are wrong. The deformations of the Lorentz group do break Lorentz invariance at high energies, that is why we call it a deformation. All these type of ideas are ad hoc and lack foundational insight. Moreover, the representation theory of these deformed Lorentz groups has still to be developed so that we obtain a new non commutative space-time picture; we are still nowhere near that. So what I would like to see is a new set of physical priniples; the Poincare group is derived from continuum, homogeneity, isotropy and causality of the vacuum. Therefore, if you think the Poincare algebra is a piece of shit because you are overpowered by renormalization problems, tell me which one of these principles fails and what type of new symmetry structures you will recover. I doubt whether these structures have anything to do with Hopf algebra's.
Concerning your comments about quantum mechanics, we need much more than just a reinterpretation, if it were only that simple. We need new mathematical structures, and no they are fairly unique and not fexible at all.
Best,
Johan
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Author Daniele Oriti replied on Mar. 15, 2011 @ 15:14 GMT
>Concerning your second mail, I will only mention the points I think are wrong. The deformations of the Lorentz group do break
>Lorentz invariance at high energies, that is why we call it a deformation.
This is false. Any deformation of the Lorentz (or Poincare) algebra I know of, in contrast to breakings of the same algebra, remain 10-dimensional at any energy and reduce to...
view entire post
>Concerning your second mail, I will only mention the points I think are wrong. The deformations of the Lorentz group do break
>Lorentz invariance at high energies, that is why we call it a deformation.
This is false. Any deformation of the Lorentz (or Poincare) algebra I know of, in contrast to breakings of the same algebra, remain 10-dimensional at any energy and reduce to the standard algebra at low energies. This is exactly what is meant by deforming the algebra with respect to some additional parameter, unless you call any modification a 'breaking' but then you are using words in a rather loose sense, which is at danger of placing very different formalisms, with very different mathematical and conceptual structure, in the same pot. The Hopf algebra of k-Poincare is an example of what I said.
>All these type of ideas are ad hoc and lack foundational insight.
This may be true, but it is a matter of rather subjective taste; they have some motivations, even though of course there is a lot to be understood about them, both mathematically and physically, and in terms of their 'foundations'. In any case the right attitude seems to me to study them more, not to drop them, until everything is clear and they have been proven right or wrong. And I am happy that lots of clever people are doing so.
>Moreover, the representation theory of these deformed Lorentz groups has still to be developed so that we obtain a new non
>commutative space-time picture; we are still nowhere near that.
I do not agree. We do know a lot about them, in the context of non-commutative geometry, and at least for some 'groups', and progressively knowing more. If we stop working on them, as a community, because we have not yet found all the answers, we will never find them. And will miss a lot, I think.
>So what I would like to see is a new set of physical priniples; the Poincare group is derived from continuum, homogeneity,
>isotropy and causality of the vacuum. Therefore, if you think the Poincare algebra is a piece of shit because you are
>overpowered by renormalization problems, tell me which one of these principles fails and what type of new symmetry structures
>you will recover. I doubt whether these structures have anything to do with Hopf algebra's.
I do not think of the poor Poincare group what you assume I do. As a general but therefore imprecise statement, what seems to be given up in non-commutative approaches, including those based on quantum group symmetries and thus Hopf algebras, is strict locality, and as a consequence a standard continuum manifold picture of spacetime (even though depending on the specific cases spacetime quantities like 'coordinates' may stay continuous). Homogeneity an isotropy are maintained, at least if you define them from an algebraic point of view (lacking a continuum manifold structure, it is not obvious what other definition one could use). Causality is tricky to define in this context, but seems to be compatible with the quantum group structure of symmetries. You may like it or not, but I am not trying to convince you to like them, only pointing out what I know of them.
>Concerning your comments about quantum mechanics, we need much more than just a reinterpretation, if it were only that simple.
>We need new mathematical structures, and no they are fairly unique and not fexible at all.
One example of which is the attempts to define quantum mechanics in absence of isometries, in absence of background spacetime at all, and for arbitrary boundaries (compact, timelike, etc). All this is slowly being developed and should not, I think, simply dismissed. Obviously, all of the above also calls for a re-interpretation, as any quantum theory of space will, but it amounts indeed to much more than that. Again, I have never stated simple re-interpretations are enough.
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Anonymous wrote on Mar. 15, 2011 @ 02:04 GMT
Finally your last message; well if you make basic errors, I tend to point them out, but I appreciate you like my succinct summary. Furthermore, there is no correct notion of locality in background independent approaches; there are however plenty of ansatze for what you would like locality to be. The problem is that none of these definitions are natural and resemble what an engineer does when has has to repair an ill constructed building.
Concerning your evaluation towards discrete approaches, I have worked on these issues for many years and actually most of the researchers I know share my opinion on this (at least in private).
Enjoy your chicken, I think the pepper sauce we just prepared will do fine.
Kind regards,
Johan
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Author Daniele Oriti replied on Mar. 15, 2011 @ 15:16 GMT
>Finally your last message; well if you make basic errors, I tend to point them out, but I appreciate you like my succinct
>summary.
It was, as you know, a concern about your style of discussion, which I am happy to see you amended. Concerning the way science works, I am aware I have still to learn a lot, but I have read my Feyerabend and Lakatos, among others, and I do...
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>Finally your last message; well if you make basic errors, I tend to point them out, but I appreciate you like my succinct
>summary.
It was, as you know, a concern about your style of discussion, which I am happy to see you amended. Concerning the way science works, I am aware I have still to learn a lot, but I have read my Feyerabend and Lakatos, among others, and I do appreciate the important role that metaphysics, feelings, principles, etc play in the construction as well as in the justification of physical theories (by the way, it is also a basic result in philosophy and history of science, beside daily scientific practice, that science does not work by deducing consequences from foundational principles, and that 'principles' come -after- one has identified the 'right' theory, most of the time). If you read again my original statement, you will see only a confirmation of this awareness.
>Furthermore, there is no correct notion of locality in background independent approaches; there are however plenty of ansatze
>for what you would like locality to be. The problem is that none of these definitions are natural and resemble what an engineer
>does when has has to repair an ill constructed building.
That a new understanding of locality is one of the open issues in most approaches is indeed a fact that I have stated from the very beginning. I also stated that there are good arguments (to me) that locality is indeed one of the concepts we have to re-think, when dealing with quantum gravity. I added that a revision of strict locality seems to be called for in all approaches I know of, whether discrete or continuum (even if of course details will change depending on the framework). I am working on this issue myself, as a testimony of my awareness of the issue, and my interest in it. I believe, as I stated above, that statement of naturalness or beauty of current attempts are important to direct ones' research, but prove nothing and are rather subjective (which is not meant to be a bad thing, but not much of a basis for convincing others). You seem to have a different judgement of the situation and on the role of locality in a more fundamental theory of spacetime. Fine. I have no problem with this. Keep working and everybody, as always, will judge from the results, of yours like of any other approach.
>Concerning your evaluation towards discrete approaches, I have worked on these issues for many years and actually most of the
>researchers I know share my opinion on this (at least in private).
Good to know. But it changes nothing. I also work and have been working on these issues for some time, and hope to continue for longer. I also talk to researches both in public and in private. It also changes nothing. I see many different opinions, interesting issues being raised to both discrete and continuum approaches, clever criticisms etc. I like this because it drives our understanding and research further.
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Anonymous wrote on Mar. 15, 2011 @ 16:21 GMT
Dear Daniele,
If your formalism allows you to consider finite open regions of space-time, then this is equivalent to inserting a classical boundary. Basically what you are probably doing is taking some fixed discrete structure, promoting this as a ''boundary'' and allow for fluctuations inside. Of course all these concepts depend at least on a background topology such as the notions of...
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Dear Daniele,
If your formalism allows you to consider finite open regions of space-time, then this is equivalent to inserting a classical boundary. Basically what you are probably doing is taking some fixed discrete structure, promoting this as a ''boundary'' and allow for fluctuations inside. Of course all these concepts depend at least on a background topology such as the notions of inside, outside and so on. And yes, such ''boundary'' would be classical in the sense that the superposition principle does not apply there, even causal set people do regard one causal set as classical. Second, such states are highly unrealistic (and distributional); even in QFT, one has that the physical states do not have a finite support.
Towards your comments on covariance, they all appear to be wrong. First of all, nobody has ever constructed a quantum Dirac algebra in 4 dimensions; as I said, the way LQG deals with these issues probably breaks covariance. In 2+1 dimensions, I grant this has been done already. Second, we do measure partial observables all the time, and never ever do we measure Dirac observables. By definition, these last ones are globally defined only unless you really add POINT particles. But then you still break manifest diffeomorphism invariance not on space-time but on the parametrization space of the point particle itself (even the free relativistic particle on Minkowski has no manifest covariant quantization, that is why we need QFT). All you seem to say is that one could quantize this in principle and define Dirac observables; even if I think this is false in 3+1 dimensions, and of course you are welcome to provide me a reference which shows me wrong, still one has no local observables for matter fields. One could have local observables for point particles but that breaks manifest reparameterization invariance and of course it is not a correct theory (probably not even mathematically).
Well, I do say you need to construct a quantum theory for matter without reference to any classical matter theory.
Concerning the terminology of asymptotic freedom, nobody I explained this to had a problem with it. Classical vacuum GR clearly is asymptotically free due to the equivalence principle (except when you meet a physical singularity of course). Take any solution and zoom in, then in a neighborhood of a point, space-time will look flat. Now, classically, if you couple point matter to gravity then the theory is not asymptotically free anymore because the Newton potential does not have an extremum at zero distance.
Concerning Einstein, I do not doubt the fact that he first tried out noncovariant approaches as Whitehead and many others did after him. However, my point was that progress was only made once he understood general covariance was a key element. That has put him in communication with Cartan and Hilbert to learn the new mathematics. So,this does not invalidate anything I said; my point was that he was messing around until he had a new idea which relegated everything he did before to the trashbin. What I told you is that any unfounded approach will suffer the same destiny; actually, axioms are the result of deep, hard work and going through the mud first. If you say you are swimming in the mud now, you will have to hope for a really original idea sooner or later, or you will get nowhere. That is how theoretical physics works.
Best,
Johan
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Anonymous wrote on Mar. 15, 2011 @ 16:38 GMT
Dear Daniele,
Concerning your second mail, did I ever dispute the fact that the q-deformed algebra's are not closed ? All I said is that they seriously differ from the Poincare algebra at high energies. Moreover, it is not enough to have the algebra only, you need to have the entire deformed group with it's complicated topology. The reason is very simple, the quantization of spin is a property of the orthochronous Lorentz group and not the algebra. And yes, I use terminology in a loose way because we have no space-time understanding whatsoever yet of these deformed algebraic structures; I invite you to construct its representation theory.
Concerning the development of this mathematical theory; yes, I am also glad people do it and I have played with these things myself once upon a time.
The development of representation theory of these deformed algebra's is still in its infancy which again does not imply it should stop, but on the other hand (and that was my point) my intuition tells me that even this kind of mathematical structures are not broad enough yet.
Concerning your statements about the motivation for the deformation, I agree with what you try to say intuitively (not physically though). Of course, all this flies straight in the face of naturalness and moreover, your deformations should be fully dynamical. Haven't seen that anywhere yet...
Best,
Johan
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Anonymous wrote on Mar. 15, 2011 @ 17:10 GMT
Finally, glad you read so many books, I never studied what philosophers of science had to say about scientific practice. Scientists themselves should find that out. As a general comment to what you say, I think that your ideas apply to most people; however they are terribly outdated what I am concerned. Ultimately, progress always comes from a new idea which of course is grounded in the failure of an older one. But what usually happens is that the later generations forget about the idea and only learn the math; this is very problematic and completely outdated. Often it is so that a masterpiece of ''engineering'' leads to new abstract insights which by themselves open a whole new world. Far too often, this new world is not studied and people stick to the engineering example. The best examples here are general relativity and quantum theory. If you do not understand what I say, I will use more words for it.
The basic problem in all attempts to formulate a principle of locality for quantum spacetime is that in the continuum, this is a topological fact which has nothing to do with the dynamics. In algebraic approaches to quantum space-time you can see very easily where the problem resides; in kappa Minkowski for example the space coordinates commute and do not commute with the time coordinate. So, first you have to define an event, are you going to say that it corresponds to eigenvectors in a representation which diagonalize the position coordinates, so that an event is effectively non-local in time? Clearly such thing is not invariant under the deformed group because time and space mix. So an event will become ''coordinate dependent'', likewise will the notion of neighborhood be. Actually, depending upon your deformation parameter, one single event in one coordinate system may stretch out formidably in another. So the laws themselves will have a non-locality scale depending upon this stretching. Of course, all such approaches seriously tamper with diffeomorphism invariance which is very poorly understood in that context (Majid once made an attempt). In my book, that reads like having an effective class of coordinate systems.
Best,
Johan
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basudeba wrote on Mar. 15, 2011 @ 23:05 GMT
Dear Sir,
You say that whether reality is digital or analog “refers, at least implicitly, to the ‘ultimate’ nature of reality, the fundamental layer.” You admit that “I do not know what this could mean, nor I am at ease with thinking in these terms.” Then how could you discuss the issue scientifically? Science is not about beliefs or suppositions. Your entire essay exhibits your beliefs and suppositions that are far from scientific descriptions. You admit it when you talk about “speculative scenario”. This is one of the root causes of the malaise that is endemic in scientific circles. Thus, theoretical physics is stagnating for near about a century while experimental physics is achieving marvelous results.
Let us take the example of space. You have not defined reality since you admit you have no idea about it. You discuss space without defining it. Both space and time are related to the order of arrangement in the field, i.e., sequence of objects and events contained in them like the design on a fabric. Both space and time co-exist like the fabric and its back ground color. The perception of each sequence is interrupted by an interval however infinitesimal. The interval between objects is called space and that between events is called time. We take a fairly intelligible and repetitive interval and use it as the unit, where necessary by subdividing it. We compare the designated interval with this unit interval and call the result measurement of space and time respectively.
Since space and time have no physical existence like particles and fields, we use alternative symbolism of objects and events to describe them. Thus, what Euclid called space is not the interval between objects, but the basic frame of reference on which the objects are placed as markers. To this extent he is right. Dedekind and others did not know this concept. Hence they wrongly held that “it is possible to construct discontinuous spaces in which Euclidean geometry holds”. Geometry is related to measurement of space and no measurement except distance (line) is possible in discontinuous spaces like in the interval between a point on Earth and another point on the Sun or Moon. However, this fallacy was not apparent to the others who built theories upon such invalid foundation. Since space is the interval between objects, the space is continuous throughout the Universe. Thus your definition of quantum space is fundamentally wrong. Hence it is no wonder that you conclude “the question has no absolute meaning, so no answer.”
The rest of your essay also exhibits the same beliefs and suppositions. Thus, it is strange that it has been highly rated by the FQXi community. Possibly “novelty of presentation (which means talking admittedly vaguely)” and incomprehensibility are the Bench marks of scientific excellence these days.
Regrds,
basudeba.
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Peter Jackson wrote on Mar. 16, 2011 @ 16:42 GMT
Daniele
I wish to warmly congratulate you on your provisional 1st place.
I hope now the 'competitive' pressure has gone we may return to good science. I'd be very appreciative if you read and genuinely commented on the model in my essay, which I beleive may be of major significance. http://fqxi.org/community/forum/topic/803
Very many thanks
Peter
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Author Daniele Oriti replied on Mar. 16, 2011 @ 23:36 GMT
Hi,
believe me, the only reason why I could not read or comment all the essays that I would have wanted had nothing to do with competitive pressure, but only with the fact that I tried to keep doing good science. As a consequence, I do not have as much time as I would want.
I'll try to read your essay, as you suggest, and let you know of comments, should I have any that could be of interest.
best,
Daniele
Edwin Eugene Klingman wrote on Mar. 16, 2011 @ 22:11 GMT
Dear Daniele Oriti,
Congratulations upon your placing first in the community voting.
Edwin Eugene Klingman
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Author Daniele Oriti replied on Mar. 16, 2011 @ 23:32 GMT
Hi,
and congratulations on your placing second! I think that finer differences do not really mean much, at this stage, and all those essays that classified roughly at the top have really been appreciated equally. Anyway, good to have our work somehow valued positively, isn't it?
ciao
Daniele
Alan Lowey wrote on Mar. 18, 2011 @ 11:56 GMT
Dear Daniele,
I share Peter Jackson's view when he says "I wish to warmly congratulate you on your provisional 1st place. I hope now the 'competitive' pressure has gone we may return to good science." I also hope that the top essay authors are still willing to consider the pesky questions of the dedicated amateurs. I have one for you which have I started with Ian Durham just recently incidentally:
Q: Coulomb's Law of electrostatics was modelled by Maxwell by mechanical means after his mathematical deductions as an added verification, which I highly admire. To me, this gives his equation some substance. I have a problem with the laws of gravity though, especially the mathematical representation that "every object attracts every other object equally in all directions." The 'fabric' of spacetime model of gravity doesn't lend itself to explain the law of electrostatics. Coulomb's law denotes two types of matter, one 'charged' positive and the opposite type 'charged' negative. An
Archimedes screw model for the graviton can explain -both- the gravity law and the electrostatic law, whilst the 'fabric' of spacetime can't. Doesn't this by definition make the helical screw model better than than anything else that has been suggested for the mechanism of the gravity force?? Otherwise the unification of all the forces is an impossiblity imo. Do you have an opinion on my analysis at all?
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Author Daniele Oriti replied on Mar. 19, 2011 @ 12:49 GMT
Dear Alan,
thanks for your interest. As I replied to Peter, the reason why I did not reply and comment to all the submitted essays and contributed ideas is simply that, whatever their interest, I have not enough time to do so. I would like to, but I simply cannot. I do not know your model, and it will take some time to study and try to understand it. Therefore I cannot comment on it. As a general remark, I do of course agree that a theory that explains gravity at a more fundamental level, which is what models of quantum space or related quantum gravity models try to do, and that in addition explains electromagnetism (electrostatics is not enough) and possibly other interactions (i.e. nuclear ones) would be better than one that only explains gravity. Unfortunately, I do not know any such complete theory yet.
Best,
Daniele
Alan Lowey replied on Mar. 20, 2011 @ 12:56 GMT
Thanks Daniele,
I have plans to include the gravity force as well. You're all right, I need a working simualtion model that canb speak for itself.
Kind regards,
Alan
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Eckard Blumschein wrote on Mar. 21, 2011 @ 05:56 GMT
Since Danielle Oriti declared having no time for replying to criticism, I will just add remarks:
He wrote: "The idea of a cosmological phase transition of space itself, replacing the Big Bang singularity, may provide a novel way to look at the puzzles of very early cosmology (horizon problem, flatness problem, etc), currently address by inflation, itself in need for a better explanation".
Such promise is of course welcome even without a tangible basis.
Danielle Oriti admitted in reply to Wilhelmus de Wilde: "Concerning singularities, indeed, several if not all practicing scientists believe the notion of singularity is but a label for a physical situation we do not understand yet, but not something physical in itself. However, the task is then to build up a theory of what happens in such situations, and unfortunately to simply deny their realities is not enough. We all have to be able to do better."
I do not just agree on that. My essay tries to show a way that does not need the coward and lazy "it depends". Instead it offers an admittedly highly unwelcome approach:
In order to do better let's focus on possible flaws in very basics of mathematics and its relationship to physics.
Admittedly I am guided by my experience as an engineer: I like using singularities - as tools -, not as something real. I am fully aware that there is no ideal line current and no ideal point charge.
Eckard
Blumschein
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Author Daniele Oriti replied on Mar. 21, 2011 @ 21:38 GMT
True, I do not have as much time as I would like to reply to all messages. Despite this, I did reply to quite a few of them, and tried both to clarify my point of view, and to counterargue some criticisms. But let me understand: what is, exactly, your ciriticism? I have tried to present a point of view according to which the answer: ''it depends'' has a clear meaning (beside the ironic tone), and it is a shorthand for ''it depends on the specific phase and regime of approximation in which quantum space is and is probed, just like in any condensed matter system, and we may have a formalism for studying all these phases and approximations, we just have to work much harder and do it properly''. So, I don't see what is cowardly and lazy about it. Beside, I don't see the use of using this type of tone and empty statements.
Daniele
Eckard Blumschein replied on Mar. 21, 2011 @ 22:42 GMT
Dear Daniele,
You wrote: "... the notion of singularity is but a label for a physical situation we do not understand yet, but not something physical in itself."
Why did you not at least try to reveal the reason for this calamity? Maybe an answer can be found here:
''it depends on the specific phase and regime of approximation in which quantum space is and is probed, just like in any condensed matter system, and we may have a formalism for studying all these phases and approximations, we just have to work much harder and do it properly''
For you and many others, mathematics including quantum space and a lot of formalisms seem to be undoubtedly correct and absolutely adequate without any (foundational) question.
You might feel my essay provocative and bold.
I found three mathematical pillars of physics affected from unjustified generalization.
Please do not hesitate taking issue if I am wrong and you have enough time.
Regards,
Eckard
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basudeba replied on Mar. 22, 2011 @ 07:08 GMT
Dear Sir,
Mr. Peter Jackson, one of the finalists had asked us some clarifications. We think it may be of interest to you. Hence we post the reply to him below your Essay.
First let us answer to your question regarding how direct observation could be different. Since you are fond of spectroscopy, we will give you an example from that branch. Look at the mechanism behind the emission...
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Dear Sir,
Mr. Peter Jackson, one of the finalists had asked us some clarifications. We think it may be of interest to you. Hence we post the reply to him below your Essay.
First let us answer to your question regarding how direct observation could be different. Since you are fond of spectroscopy, we will give you an example from that branch. Look at the mechanism behind the emission spectra and absorption spectra. Both the emitter and the observer are in the same bigger frame of reference linking both and separated by the field. You will admit that the scattering in the medium causes the difference.
You say: “direct light hitting the eye is also scattered.” In our theory, different forces co-exist. Thus, it is not scattering, but comparison like when we measure (compare) the length of a rod by a scale. The scale is not scattered by the rod. When you say “it can be apparent when we move”, you are falling into the trap laid by Einstein. We have discussed it elaborately earlier by giving the example of Eddington.
You have not defined dark matter or dark energy precisely. The phenomena cited by you as proof is indirect and not direct. We can explain those phenomena differently. You also admit this possibility indirectly when you say: “The plasma does the precise job our imaginary 'dark matter' does, and in the same places!”
You say: “The references again show that curved space time exactly matches the effects of diffraction (gentle refraction delays and path curvature) via scattering in plasma.” We have given our interpretation of “curved space-time”, which is different from GR and it can also explain the effects of diffraction equally correctly.
You say: “The separate terms plasma-sphere and ionosphere are really misnomers”. But you admit their difference when you say: “they are a graded whole, proton rich low down and electron rich higher up.” The grading is not smooth, but shows the same distribution like the arrangement of protons and electrons in an atom. Since protons and electrons are placed differently in nucleus and orbits, the plasma-sphere and ionosphere have to be treated as different. We divide the electric and magnetic fields into four types each based on their gradient. That, along with the interaction with the Solar wind will explain the rest of your comments.
Now we will explain 'velocity of the field', which also will explain the constancy of ‘c’. We have already explained that the basic nature of the field is equilibrium. The basic nature of forces is displacement. This gives rise to two different types of inertia: inertia of motion due to forces and inertia of restoration (elasticity) due to the field. This leads to both these inertia acting against a point of equilibrium to create locally confined structures. These structures, which are nothing but confined field is called “rayi”. Both the inertias further act on “rayi”. In such a scenario, the combined effect leads to repeated confinement around the point of equilibrium. The confined structures in which inertia of restoration dominates, is called particle (moorty). In the opposite case, it is called “amrita”. This can be considered as your DFM.
The confinement could be strong, weak or loose, which leads to the formation of solids, fluids (including gases) and plasma. We call these ‘dhruva”, “dhartra” and “dharuna” respectively. Where the inertia of motion dominates, it appears as heat. Depending upon the nature of the particles, the propagation of heat is also classified into three categories. In solids, plasma and fluids, these are done by conduction, radiation and convection. We call these as “nirbhuja”, “pratrirnna” and “ubhayamantarena” respectively. The third category gives rise to the electric field. Thus, electric behaves like a hot fluid.
Till now we were discussing about the confinement of “rayi” (where inertia of restoration dominates). In the opposite case, where inertia of motion dominates, “rayi” gives rise to three corresponding forces of cold confinement. These can explain the effects of the so-called “dark matter and dark energy”. Magnetism belongs to this category. Thus, magnetism is a cold confining force. Since both these are different states of “rayi”, electricity and magnetism are two sides of the same coin.
Till now we were discussing “rayi”, which is a part of the primordial field dominated by inertia of restoration. The other part is dominated by inertia of motion, which we call “praana”. The effect of this is felt by other bodies. Hence this gives rise to force. Depending on their effects on different bodies, these forces are classified into different groups discussed earlier. While strong, weak, electromagnetic and radioactive disintegration forces belong to this category associated with inertia of motion and heat, gravitational interaction is associated with inertia of restoration and cold. Thus, they cannot be united.
After a part of the primordial field is confined within “rayi”, inertia of restoration in the field becomes weak and inertia of motion dominates. Thus, the field generates waves that expand rapidly in all directions. You call this big bang. The effects of “rayi” and “praana” in the primordial medium create the bow shock effect. This leads to reduced velocity of the wave, which ultimately stabilizes, cutting off a vast volume which we call universe. Since there is no reason to believe that it happens only in our locality, we believe in multiverses, which are similar universes and not as described by MWI.
After the bow shock comes to rest, the forces of inertia of motion and inertia of restoration cancel each other leading both to a superposition of states. We call this “maayaa”. But the equilibrium is momentary, since the balance between “rayi” and “praana” within the confinement of “maayaa” has not been equated, the next moment inertia of restoration dominates and there is massive contraction. You call this inflation. We call this force “dhaaraa”. This creates further interaction, which leads to structure formation. We call this “jaayaa”. Outside the structures, the inertia of restoration still dominates. You call it the cosmic microwave back ground radiation. We call it “aapah”. Thus, the universe can be picturised as an ocean containing many islands. The galaxies can be imagined to float in an “ocean” called “saraswaan”, the stars can be imagined to float in an “ocean” called “nabhaswaan”, and the Earth like planets can be imagined to float in an “ocean” called “samudra arnava”.
Just like the Earth orbits the Sun and spins around its own axis due to the combined effects of the Sun’s movement and that of the inter-stellar medium that move in different directions on the one hand, the different magnetic fields on the other hand (in a broader scale, these are the effects of “rayi and praana” and “dhaaraa and jaayaa”), the Universe as a whole also moves within the confines of “maayaa”. This appears as the receding galaxies, just like the planets sometimes appear to move away from each other. This movement of the Universal field is constant for all structures. This is what you describe as “space has inertia and angular momentum.”
It is well known that objects are perceived only during transition. The transition can be of two types: the object can move or the field containing the object can move while the object is stationary (both together are also possible, but they fall into these two groups). In the case of electromagnetic field in space, it is the field that moves at a constant velocity. You also admit it when you say: “ALL matter in motion is in motion with respect to a LOCAL background. Light entering the galaxy is Doppler shifted by the Halo to the galaxies 'c', again at the heliopause to the Sun's 'c', and at the Ionosphere to the Earths 'c', and on ad infinitum.” The only difference is that you presume the particle is moving at ‘c’ with respect to the back ground, which you take as at rest. We take the opposite view of the background with us moving at ‘c’. Like we do not experience the motion of the Earth, but think the Sun and the stars are orbiting it, we do not experience the motion of the back ground since we are also moving with it. But the effects in both cases are the same.
Regarding the 3 frames, you are on the right track. Here we quote from one of our posts under the Essay of Mr. Rafael Emmanuel Castel, where we had commented elaborately about Einstein’s 1905 paper.
Einstein: We assume that this definition of synchronism is free from contradictions, and possible for any number of points; and that the following relations are universally valid:
3. If the clock at B synchronizes with the clock at A, the clock at A synchronizes with the clock at B.
4. If the clock at A synchronizes with the clock at B and also with the clock at C, the clocks at B and C also synchronize with each other.
Thus with the help of certain imaginary physical experiments we have settled what is to be understood by synchronous stationary clocks located at different places, and have evidently obtained a definition of “simultaneous”, or “synchronous”, and of “time”. The “time” of an event is that which is given simultaneously with the event by a stationary clock located at the place of the event, this clock being synchronous, and indeed synchronous for all time determinations, with a specified stationary clock.
Our comments: Einstein sets out in the introductory part of his paper: “…the phenomena of electrodynamics as well as of mechanics possess no properties corresponding to the idea of absolute rest. They suggest rather that, as has already been shown to the first order of small quantities, the same laws of electrodynamics and optics will be valid for all frames of reference for which the equations of mechanics hold good. We will raise this conjecture (the purport of which will hereafter be called the “Principle of Relativity”) to the status of a postulate…”. The “Principle of Relativity” is restricted to comparison of the motion of one frame of reference relative to another. Introduction of a third frame of reference collapses the equations as it no longer remains relativistic. The clock at B has been taken as a privileged frame of reference for comparison of other frames of reference. If privileged frames of reference are acceptable for time measurement, then the same should be applicable for space measurement also, which invalidates the rest of the paper.
Simultaneity refers to occurrence of more than one action sequences, e.g.; events, which measure equal units in two similar action sequence measuring devices, e.g.; clocks, starting from a common reference point, e.g.; an epoch. It is the opposite of successive events. Synchronisation refers to the readings of more than one clock (or interval between event from an epoch), which do not require “clock correction”, i.e.; when such readings are compared with a common or identical repetitive action sequence or action sequence measuring devices, their readings match. It is not the opposite of successive events, but can also be simultaneous – for example, two clocks synchronised with each other will give similar readings simultaneously. If one of the clocks give 24 hour reading while the other gives 12 hour reading, then half of the time they will give readings that are synchronized and simultaneous, while half of the time they will not be so. Yet, the results can be made to synchronize by deducting 12 hours from any reading beyond it in the clock giving 24 hours reading. Here the clocks will be synchronized through out, but give simultaneous readings alternatively in succession or otherwise.
In the definition of simultaneity given by Einstein, the two clocks situated at two distant points in the same frame of reference (whether the frame of reference is inertial or not is not relevant as both the clocks and points P and P’ are fixed in the frame) are said to be synchronous, if their readings of the identical events in both clocks match. This only refers to the accuracy of mechanical functioning of the clocks and uniformity of the time unit used in both the clocks. This definition is nothing but telling the obvious in a complicated and confusing manner. Since the two clocks are synchronised, they should record equal time in both the frames of reference over equal interval.
We have also shown that if we follow the logic of Einstein, then we will land in a problem like the Russell’s paradox of set theory. In one there cannot be many, implying, there cannot be a set of one element or a set of one element is superfluous. There cannot be many without one meaning there cannot be many elements, if there is no set - they would be individual members unrelated to each other as is a necessary condition of a set. Thus, in the ultimate analysis, a collection of objects is either a set with its elements or individual objects, which are not the elements of a set.
Let us examine set theory and consider the property p(x) : x x, which means the defining property p(x) of any element x is such that it does not belong to x. Nothing appears unusual about such a property. Many sets have this property. A library [p(x)] is a collection of books. But a book is not a library (x x). Now, suppose this property defines the set R = {x : x x}. It must be possible to determine if RR or RR. However if RR, then the defining properties of R implies that RR, which contradicts the supposition that RR. Similarly, the supposition RR confers on R the right to be an element of R, again leading to a contradiction. The only possible conclusion is that, the property “x x” cannot define a set. This idea is also known as the Axiom of Separation in Zermelo-Frankel set theory, which postulates that; “Objects can only be composed of other objects” or “Objects shall not contain themselves”.
In order to avoid this paradox, it has to be ensured that a set is not a member of itself. It is convenient to choose a “largest” set in any given context called the universal set and confine the study to the elements of such universal set only. This set may vary in different contexts, but in a given set up, the universal set should be so specified that no occasion arises ever to digress from it. Otherwise, there is every danger of colliding with paradoxes such as the Russell paradox, which says that “S is the set of all sets which do not have themselves as a member. Is S a member of itself?” Or as it is put in the everyday language: “A man of Serville is shaved by the Barber of Serville id and only if the man does not shave himself?” Such is the problem in Special theory of Relativity.
Thus, “when we have to connect in time series of events occurring at different places, or - what comes to the same thing - to evaluate the times of events occurring at places remote from the watch”, we must refer to a common reference point for time measurement, which means that we have to apply “clock corrections” to individual clocks with reference to a common clock at the time of measurement which will make the readings of all clocks identical. (Einstein has also done it, when he defines synchronization in the para below). This implies that to accurately measure time by some clocks, we must depend upon a preferred clock, whose time has to be fixed with reference to the earlier set of clocks whose time is to be accurately measured. Alternatively, we will land with a set of unrelated events like the cawing of a crow and falling of a ripe date palm simultaneously. A stationery clock and a clock in a moving frame do not experience similar forces acting on them. If the forces acting on them affect the material of the clock, the readings of the clocks cannot be treated as time measurement. Because, in that case, we will land with different time units not related to a repetitive natural event - in other words, they are like individual elements not the members of a set. Hence, the readings cannot be compared to see whether they match or differ. The readings of such clocks can be compared only after applying clock correction to the moving clock. This clock correction has nothing to do with time dilation, but only to the mechanical malfunction of the clock.
There is nothing like empty space. Space, and the universe, is not empty, but full of the Cosmic Background Microwave Radiation from the Big-Bang. In addition to this, space would also seem to be full of a lot of other wavelengths of electromagnetic radiation from low radio frequency to gamma rays. This can be shown by the fact that we are able to observe this radiation across the gaps between galaxies and even across the “voids” that have been identified. Since the universe is regarded as being homogeneous in all directions, it follows that any point in space will have radiation passing through it from every direction, bearing in mind Olber’s paradox about infinite quantities etc. The “rips” in space-time that Feynman and others have written about are not currently a scientifically defined phenomenon. They are just a hypothetical concept - something that has not been observed or known to exist. Thus, “light signals, given out by every event to be timed, and reaching him through empty space” would be affected by these radiations and get distorted.
Regards,
basudeba
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Anonymous replied on Mar. 22, 2011 @ 15:19 GMT
Dear Basudeba,
I see you have understood the problem of self-referential statements and connected it to relativity ... Indeed, Einstein's theory does not offer a way out of that, but all I want to say is that your statements are not in conflict with Einstein's equivalence principle; they are just contradictory to GR.
Concerning your evaluation of the work at hand; it is indeed exemplary of the modern culture where vague statements are cultivated and interpreted as a sign of presumed intelligence. It goes even deeper than that, those people will defend themselves by saying they are politically correct, while the simple truth is of course that the emperor has no clothes. I, on the other hand, say that whatever space-time picture you want, it has to be constructed from whatever representation of a totally ordered number system containing the reals. Of course, people then might still want to defend the discrete attitude by saying you can construct the reals from the naturals, but of course this is not a finite construction. Point is that nature cannot be locally finite a priori without any reference to the continuum or infinity.
Now, you may ask, do I have a strict mathematical proof of this? Well then, let me ask you for a mathematical proof that planets are not kept in their orbital motion by means of little angels. Physics does not operate in this way, alas very few are willing to accept that and reading books of Feyerabend is not going to help anybody in this matter.
Best,
Johan
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basudeba replied on Mar. 22, 2011 @ 23:42 GMT
Dear Sir,
You must be congratulated for maintaining your stand.
In the essay, you admitted that “I do not know what this could mean, nor I am at ease with thinking in these terms.” You are showing the same ignorance and unease in replying to the points raised by us - both on your essay and on the comments of Mr. Jackson.
In stead of long political dialogues, kindly give specific and scientific replies raised by us or express your inability to address the points. There is no need to advertise your ignorance and unease in discussing scientific topics.
Regards,
basudeba.
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Author Daniele Oriti replied on Mar. 22, 2011 @ 23:53 GMT
I have no trouble expressing my inability to address the points you raised, because I do not think I understood what the scientific points to be addressed are. This must be certainly due to my own limitations. As you know, nobody is perfect and we should not pretend to be. I do not think I can fruitfully contribute to this nice, profound and instructive discussion you are having in the comments tread to my essay, but feel free to continue. The use of a certain tone and a certain style of statements only improves the interest and quality of your exchange. So, please keep going....and thanks a lot for contributing so much.
Anonymous replied on Mar. 23, 2011 @ 01:06 GMT
Dear Daniele,
The question about who contributes is always a historical one and the choice which sauce accompanies the chicken the best is only agreed upon once sufficient people know its virtues. However, matters of style and tone have never been imperative to scientific progress although they seem to be terribly important for your personal well being. I always find this kind of limitations more annoying than the scientific ones.
Kind regards,
Johan
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Anonymous wrote on Mar. 24, 2011 @ 15:32 GMT
Caro Daniele
Your essay concentrates on quantized space - but should not the building blocks of space be the also the same as those making up matter?
In a recent post above you said "As a general remark, I do of course agree that a theory that explains gravity at a more fundamental level, which is what models of quantum space or related quantum gravity models try to do, and that in addition explains electromagnetism (electrostatics is not enough) and possibly other interactions (i.e. nuclear ones) would be better than one that only explains gravity. Unfortunately, I do not know any such complete theory yet."
I have presented just such a theory but it is incomplete say the least. Moreover for my model to function some basic notions of present-day physics (specifically GR, the notion of flexible space-time, the point photon, and of quantum probability) have to be reconstructed or reverse-engineered to a common and simpler theory - In my 2005
Beautiful Universe theory on which my present fqxi paper is based, a universal lattice of dielectric building blocks store angular momentum in units of h and transmit it to neighboring nodes. Gravitational potential (density) is caused by the rate of rotation of the nodes, and the pattern of twisting of the axes of rotation in the lattice. I would highly appreciate it if you can look at my ideas. They would only work if professionals like you pick them up and work out the details!
With best wishes for your success, Vladimir
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Steve Dufourny wrote on Mar. 24, 2011 @ 21:33 GMT
Hi dear Daniele,
I had not read your essay, now yes, It's full of interesting things. Congratulations,and good luck for the final.
Steve
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Author Daniele Oriti replied on Mar. 25, 2011 @ 23:46 GMT
Well, thanks a lot for reading it, and for your kind message. I am happy you liked it.
ciao
Daniele
Steve Dufourny replied on Mar. 26, 2011 @ 11:21 GMT
Ciao Daniele,
You are welcome,sincerely.
All the best.
Steve
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Author Yuri Danoyan+ replied on Apr. 20, 2011 @ 11:47 GMT
Dear Daniele
What is your prognoses about Fermilab experiment?
http://holometer.fnal.gov/
http://www.fnal.gov/dir
ectorate/program_planning/Nov2009PACPublic/holometer-proposa
l-2009.pdf
All the best
Yuri
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Alan Lowey wrote on Mar. 26, 2011 @ 10:43 GMT
Hello Daniele,
I have another bugging question for you. I'm 100% convinced that this proposed 'inclination hypothesis' will be 100x more enlightening than the Archimedes screw model for the graviton/anti-graviton. It's a real eye-opener this one.
The precession of Mercury can be explained in the same way that the 100,000 year glacial cycle can be explained by the inclination hypothesis that has reduced tide raising forces with increased inclination. The reduced tides lowers the distribution of warm equatorial waters to the poles, which induces glaciation in the high latitudes. The combination of these two papers
Spectrum of 100-kyr glacial cycle: Orbital inclination, not eccentricity and
The 1,800-year oceanic tidal cycle: A possible cause of rapid climate change can be used to reconcile the 1,800 year cycle to the 1,470 year cycle seen in physical data
Timing of Abrupt Climate Change: A Precise Clock.
I've scanned a quick doodle from last night which shows how the planet Mercury, due to it's high eccentricity, has very different distances above and below the orbital plane when nearing the planet and when furthest away. This means that the tide raising forces will be very different from one half of it's inclination orbit compared to the other half, despite it only having an inclination angle of around 6 degrees. This difference in gravitational forces from the calculated Newtonian forces is the reason for the discrepancy of it's orbital precession. I need to do the calcs, I know.
This proposed increase in gravitational attraction on the rotational plane of a celestial body has a surprising number of possible examples. This article on the
Pan and Atlas moons of Saturn mentions the problem of their formation from ring debris alone, it simply wouldn't happen under the gravity laws. They say that a gravitational 'seed' would be needed which is exactly the same conclusion that the Harvard professors came to when analysing their 360 mile wide innermost core of the Earth
Earth's New Center May Be The Seed Of Our Planet's Formation.
Kind regards,
Alan
attachments:
1_Doodle.jpg
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Author Yuri Danoyan+ wrote on Mar. 30, 2011 @ 12:13 GMT
Gentlemens
I wonder why you did not notice or do not want to notice the radical view that an independent investigator.Remember this name: name,Friedwardt Winterberg
http://bourabai.narod.ru/winter/relativ.htm
http://
bourabai.narod.ru/winter/clouds.htm
Yuri Danoyan
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Alan Lowey replied on Mar. 30, 2011 @ 16:29 GMT
Hi Yuri,
Yes, Professor Wintergerg has got it to a tee. Spot on. Sorry for not looking sooner, although I find a direct link tends to aid a reader, such as
The Einstein-Myth and the Crisis in Modern Physics (see link help page above).
I want to email him a.s.a.p and tell him about the Inclination Hypothesis. He'll love it, I'm sure.
Cheers Yuri,
Alan
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Alan Lowey wrote on Mar. 31, 2011 @ 10:26 GMT
I've taken the liberty of scanning
Professor Taylor's new book where he talks about the current concensus opinion on the cause of the 100,000 year ice age cycle. It's a brillint summary of the situation as it stands. See attached and also attached to the next post.
Alan
attachments:
1_Dance_Of_Air__Sea1.jpg,
1_Dance_Of_Air__Sea2.jpg
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Alan Lowey wrote on Mar. 31, 2011 @ 10:26 GMT
Shaikh Raisuddin wrote on Jul. 18, 2018 @ 18:44 GMT
The question, Is Reality Digital or Analog? is misleading like chicken and egg. All closed answer question carry risks of incorrect direction.
Reality is both digital and analog.
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