On The Flow of Time by George F R Ellis

[deleted]

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

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

Fine.

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

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

What is the intended application of your ideas?

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

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

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

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

Dimi Chakalov

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

D.C.

[deleted]

George,

Thank you.

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

THANK YOU,

Brian Beverly

[deleted]

Dear Brian Beverly

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

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

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

[deleted]

Dear George Ellis,

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

Vesselin Petkov

[deleted]

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

[deleted]

George,

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

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

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

"On this view, infinities are mathematical entities that never occur in physical reality; this may be taken as applying to the nature of space in a profound way."

2. George Ellis (Dec. 9, 2008 @ 22:41 GMT)

"The whole point of my article is that there do not exist any completely isolated systems in the real world (except perhaps the universe itself)."

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Comment #1: You quoted David Hilbert in [1] above, so please show that infinities do not, and cannot occur in describing 'the only truly isolated system' -- the universe itself. It is ONE signle system, and it should require "infinities" for its description.

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3. George Ellis (Dec. 4, 2008 @ 10:00 GMT):

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

4. On Carlo Rovelli's thread,

http://fqxi.org/community/forum/topic/237

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

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

5. On Carlo Rovelli's thread,

http://fqxi.org/community/forum/topic/237

George Ellis wrote (Dec. 15, 2008 @ 05:16 GMT)

"Objectively privileged hypersurfaces do indeed exist in standard cosmology, and in all physically realistic solutions."

6. George Ellis (Dec. 12, 2008 @ 06:18 GMT):

"Perhaps this is because all these equations are effective equations deriving from a single deeper unified theory, and it is this common origin that leads to the different times being being consistent.How this could all arise from a unified theory of quantum gravity and fundamental interactions is then what needs clarity."

7. George Ellis (Dec. 4, 2008 @ 05:21 GMT)

"You can't talk about time at all without using the concept of time. My paper is based on how standard quantum theory in fact implies the flow of time in an ireversible way. This is one of the best tested theories in physics."

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Comment #2.1: If you wish to talk quantum cosmology, by applying quantum theory to 'the universe itself' (cf. your note [2] above), then I might agree with your conjecture in note [6]. But you will need some brand new quantum theory, not the textbook one, mentioned in [7].

Comment #2.2: If you do not wish to talk quantum cosmology, the task of your whole essay is ultimately focused on your note [3], "how proper time relates to coordinate time as we move to the future", given some "preferred time variable in GR" (note [4]) on some "objectively privileged hypersurfaces" (note [5]).

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8. On Carlo Rovelli's thread,

http://fqxi.org/community/forum/topic/237

George Ellis wrote (Dec. 16, 2008 @ 12:01 GMT)

"... enabling the physical states of our neurons to succeed each other in timelike succession in a suitable causally patterned way, there is no way that consciousness can progress from one state to another."

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Comment #3:

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

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I wish you best of luck with clarifying the objectives of your essay. If you wish to suggest, after Bill Unruh, that there should exist some "explicit (but unmeasureable) time"), please be more specific in its derivation, and then try to imagine how your ideas might help in understanding the gravitational energy -- the proof of the pudding, you know.

Dimi Chakalov

[deleted]

Dear Professor Ellis,

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

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

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

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

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

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

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

Regards,

Eckard Blumschein

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George,

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

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

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

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

[deleted]

Dear George,

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

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

Best wishes

Peter

[deleted]

Dear George Ellis,

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

Thank you for the helpful and constructive discussion. I have been trying to examine the Evolving Block Universe (EBU) view as thoroughly as possible since it is the only serious alternative to the usual Block Universe (BU) view. And I believe we are all interested in understanding the world no matter who will turn out to be holding the correct view. I will do what can be done here in order not to make the posts unreasonably long. In any case, in the spring I plan to complete a paper on the EBU, based on my talk at the third spacetime conference dedicated to Minkowski's anniversary last June in Montreal, and if you are interested I will send you a copy.

1. I completely agree that "The problem with this [Weyl's] view is fundamental". His view has been quoted so many times but, to my knowledge, no one has gone further than that. I briefly addressed your objection to this view in my book "Relativity and the Nature of Spacetime" (Springer, 2005) and intend to elaborate more on it in the second edition planned for the late spring of 2009.

I think it is clear that before discussing Weyl's conjecture one should determine what is the world - EBU or BU; if it is EBU the flow of time is objective, not minddependent, and there is no need for what Weyl proposed. It seems Weyl did not see any alternative to the BU. And indeed if the world turns out to be BU, Weyl's idea appears to be the only reconciliation of the BU and the fact that we realize ourselves at the moment 'now'. Then we have to ask the type of questions you mentioned. And there are several possibilities. The brain processes are governed by the laws of physics (although not all agree), but neuroscience does not offer a certain answer to the question whether those processes constitute what we call consciousness (or what Weyl had in mind).

2. On what you wrote "The fundamental irreversibility of the quantum measurement process (you don’t even have a prediction of probabilities in the backwards direction of time) is a key aspect of what is going on." I think this is an important point that might lead to misunderstanding. I think (i) whether or not something is reversible and (ii) whether or not we can predict something, have nothing to do with the alternative EBU - BU. It is not unthinkable to imagine a BU that is asymmetric and acausal (at least at the micro scale) since existence of objects in such a world is not determined by causality (I think existence is more fundamental than causality).

3. Another important point that can lead to misunderstanding: yes, I am aware of "The key aspect of all these special relativity examples is the radar definition of simultaneity" (your book “Flat and Curved Spacetimes” with Ruth Williams is one of my favorite books on relativity and as such is quoted in my essay). But I tried to emphasize that we should attempt to understand the world itself (of course, on the basis of our experiments and observations). That is why I proposed a thought experiment that involves an *instantaneous* measurement of length contraction and no radar procedure is used. It is described in my book mentioned above (p. 138) and also briefly in another paper (Sec. 3).

Very briefly - two observers A and B in relative motion have meter sticks oriented along the line of their relative motion. So the meter sticks are parallel (with 1mm between them) when their middle points instantaneously "coincide". Let us call this event M (meeting). Along the length of A's meter stick there are lights mounted on it. At event M all lights are simultaneously red in A's reference frame (say, this was the present meter stick for A at M - all in red). Before M, all lights in A's reference frame were green (all past meter sticks for A were green); after M, all lights in A's reference frame were blue (all future meter sticks for A will be blue).

Along B's meter stick there are cameras mounted on it. At M all cameras take snap shots simultaneously in B's reference frame. So, at M, A's meter stick will be red for A, but B will look at the pictures and will see that A's meter stick is green-red-blue (past-present-future existing at once for B as a different three-dimensional meter stick). I fully realize that this instantaneous measurement is not a crucial argument against the EBU since we can observe the results only after all pictures of A's meter stick came into existence. But it demonstrates that instantaneous experiments can be carried out in relativity; the twin paradox (when the twins meet and compare their clocks) is also such an experiment. See also the next point.

3. What I meant when I wrote that "the evolving block universe is as predetermined as the block universe since the growing block universe will be merely actualizing the forever given events of the block universe" can be demonstrated in the case of the above thought experiment. At the diagram attached to my previous post at Carlo Rovelli's forum, the event P_B (the blue end point of what B measures) has not yet come into existence according to the EBU, but it is certain it will be blue. While one could argue here that it may turn out that that light might malfunction, etc., the EPR-type experiments are a better example - when the polarization of a photon is measured, the measurement of the other photon (spacelike separated) might not yet have come into existence, but the outcome is certain (predetermined).

4. "Please enlighten me as to how this leads to the definite prediction of the outcomes of *all* quantum experiments". I never said "definite predictions" - on the contrary, one can have both - probabilistic predictions and a forever given spacetime picture of the probabilistic behaviour of the quantum object and the measurement process. The idea is very briefly explained in Sec. 5 of my essay, but there are references there. At least you will see (i) an unexpected explanation of the double-slit experiment, and (ii) that I have not forgotten that experiment.

5. Interestingly, I see the problem exactly where you do not see it: "There is no contradiction with special relativity effects, basically because the surfaces of coming-into-being do not have to coincide with any specific observer's determination of surfacves of simultaneity in spacetime." As "the surfaces of coming-into-being" are *objectively* privileged (the edge of EBU) only *one* such surface is possible; more surfaces imply relativization of existence (to avoid any misunderstanding - by a surface I mean a spacelike cross-section of the "whole" universe, of everything that exists).

Finally, I wonder, on the EBU view, what was an electron before it hit the screen in the double-slit experiment? The past is there; so the electron should be something in the already realized spacetime block.

Vesselin Petkov

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

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

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

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

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

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

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

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

all the best

[deleted]

Dear Peter Lynds

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

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

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

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

[deleted]

Dear Vesselin Petkov

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

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

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

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

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

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

[deleted]

Philip,

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

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

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

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

[deleted]

Dear Vesselin Petkov

Continuing my response to your post,

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

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

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

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

[deleted]

Dear Philp Gibbs

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

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

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

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

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

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

[deleted]

Thanks for your answers.

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

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

[deleted]

Dear George,

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

Best wishes

Peter

[deleted]

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

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

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

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