Julian Barbour on does time exist

[marcus]

Hi Ruta, thanks for joining the conversation. Nice to hear from you! You quoted Rovelli's September 2012 paper, in which he defines and uses several types of TIME.

What can it mean to say "spacetime fluctuates"...?

Well you are quoting Rovelli so your question is what does HE mean, so you could write and ask him. But I will venture to suggest that what he means is the spacetime geometry cbanges with the passage of time.

I had better copy the abstract and the passage to give context to what you were quoting. Certainly one does not have to have a 4D block universe with a physically meaningful time coordinate being one of the dimensions merely in order to model change with the passage of time. You in particular would be expected to know this better than many others, including myself. But here in this paper we have no lack of times: proper time, and thermal time, and a local version involving a local hamiltonian.

You have many choices for what fluctuation can mean, of course, since you have several opportunities to describe things as changing with the passage of time.

I think in that page 1 paragraph it is meant in a general sense without specifying the particular time-evolution. But anyway I will copy the material to get it all together where we can look at it:
http://arxiv.org/abs/1209.0065
General relativistic statistical mechanics
Carlo Rovelli
(Submitted on 1 Sep 2012)
Understanding thermodynamics and statistical mechanics in the full general relativistic context is an open problem. I give tentative definitions of equilibrium state, mean values, mean geometry, entropy and temperature, which reduce to the conventional ones in the non-relativistic limit, but remain valid for a general covariant theory. The formalism extends to quantum theory. The construction builds on the idea of thermal time, on a notion of locality for this time, and on the distinction between global and local temperature. The last is the temperature measured by a local thermometer, and is given by kT = [STRIKE]h[/STRIKE] dτ/ds, with k the Boltzmann constant, [STRIKE]h[/STRIKE] the Planck constant, ds proper time and dτ the equilibrium thermal time.
9 pages. A tentative second step in the thermal time direction, 10 years after the paper with Connes. The aim is the full thermodynamics of gravity. The language of the paper is a bit technical: look at the Appendix first.

==1209.0065 page 1 excerpt==
Thermodynamics and statistical mechanics are powerful and vastly general tools. But their usual formulation works only in the non-general-relativistic limit. Can they be extended to fully general relativistic systems?

The problem can be posed in physical terms: we do not know the position of each molecule of a gas, or the value of the electromagnetic field at each point in a hot cavity, as these fluctuate thermally, but we can give a statistical description of their properties. For the same reason, we do not know the exact value of the gravitational field, which is to say the exact form of the spacetime geometry around us, since nothing forbids it from fluctuating like any other field to which it is coupled. Is there a theoretical tool for describing these fluctuations?

The problem should not be confused with thermodynamics and statistical mechanics on curved spacetime. The difference is the same as the distinction between the dynamics of matter on a given curved geometry versus the dynamics of geometry itself, or the dynamics of charged particles versus dynamics of the electromagnetic field. Thermodynamics on curved spacetime is well understood (see the classic [1]) and statistical mechanics on curved spacetimes is an interesting domain (for a recent intriguing perspective see [2]). The problem is also distinct from “stochastic gravity” [3, 4], where metric fluctuations are generated by a Einstein-Langevin equation and related to semiclassical effects of quantum theory. Here, instead, the problem is the just the thermal behavior of conventional gravity.¹
A number of puzzling relations between gravity and thermodynamics (or gravity, thermodynamics and quantum theory) have been extensively discussed in the literature [5–14]. Among the most intriguing are probably Jacobson’s celebrated derivation of the Einstein equations from the entropy-area relation [15, 16], and Penrose Weil-curvature hypothesis [17, 18]. These are very suggestive, but perhaps their significance cannot be evaluated until we better understand standard general covariant thermodynamics.
==endquote==[/QUOTE]

 

[RUTA]

Hi Ruta, thanks for joining the conversation. Nice to hear from you! You quoted Rovelli's September 2012 paper, in which he defines and uses several types of TIME.

Well you are quoting Rovelli so your question is what does HE mean, so you could write and ask him. But I will venture to suggest that what he means is the spacetime geometry changes with the passage of time.

Thanks for the reply, marcus. I don't see an answer in Rovelli's quote, so I'm hoping someone here can shed some light on the meaning of "spacetime fluctuations." I hear this phrase often so it must mean *something* to someone.

In your take, you say "spacetime geometry changes with the passage of time." Thus, we have different spacetime geometries which are ordered 'temporally' and you have introduced a 5th (and temporal) dimension. [Since spacetime contains all of Rovelli's definitions of time, the time of the temporal ordering is not one of them.] What does this mean to us empirically?

 

[marcus]

... I'm hoping someone here can shed some light on the meaning of "spacetime fluctuations." I hear this phrase often so it must mean *something* to someone.

I see! You hear the phrase often, from different people in different contexts. I don't suppose it always means the same, or is used the same way. So I don't see how I can set your mind at rest. One has to see how a given author translates the idea into mathematics.

Purely verbal description has a certain vagueness--the common-language meaning, i.e. the usage, "fluctuates" one might say So often, I imagine, one has read further into any given article to see mathematically what is intended.

Here is the passage which I think you are saying you do not understand. It is on page 1, early in the introduction of the article, where an author often speaks in general terms about what will be made mathematiclly precise later.

== http://arxiv.org/abs/1209.0065 page 1 excerpt==
Thermodynamics and statistical mechanics are powerful and vastly general tools. But their usual formulation works only in the non-general-relativistic limit. Can they be extended to fully general relativistic systems?

The problem can be posed in physical terms: we do not know the position of each molecule of a gas, or the value of the electromagnetic field at each point in a hot cavity, as these fluctuate thermally, but we can give a statistical description of their properties. For the same reason, we do not know the exact value of the gravitational field, which is to say the exact form of the spacetime geometry around us, since nothing forbids it from fluctuating like any other field to which it is coupled. Is there a theoretical tool for describing these fluctuations?
==endquote==

Now as it stands this bit of the introduction could be talking about different sorts of variation. Later on this particular article introduces some notions of temporal variation. Not of the "block universe" sort, or where there is a global foliation! But observer proper time is mentioned, and "many-fingered time" and local foliation (slicing) under specific conditions---so one can talk about temporal variation and make it precise in different ways, in the context of this paper.

But that is later on! What I think you are saying you do not understand (and want someone to give you a meaning) is this bit of the introduction. As it stands it could be talking about different sorts of variation, as I said. There could be variation in terms of SCALE, for instance. The field could appear to fluctuate randomly not with time but as you narrow down and zoom in. And that is not the only sort of non-temporal variation in geometry that the author might have had in mind! If it were Laurent Freidel, he might have been thinking of the variation of spacetime geometry depending on the observer's VANTAGE POINT. Freidel has argued that there does not exist a unique spacetime for all observers but according to "relative locality*" each has his own phase space and Freidel deduces empirically testable consequences from this. It is a bit exotic and I have forgotten the details but it came out last year and has not gone away. Anyway there can be different sorts of non-temporal variation of spacetime geometry---it can differ ala Freidel from observer to observer and according to the scale at which a given observer examines the spacetime geometry. As an expert you probably are aware of other types of non-temporal fluctuation that I can't think of at the moment.

But with Rovelli's introduction to his September 2012 paper, I think it is simpler than that. If you read on into the paper you will see, I imagine, that he is only talking about types of TEMPORAL variation, in a strictly 4D context (no 5th dimension ) of spacetime geometry, whether it be, say, as experienced by a single observer in one locale, or by a many-fingered multitude of observers, or defined according to this interesting "thermal time" concept. Temporal, in other words, but not assuming a fixed global foliation.

Please let me know if I am missing something in my reading of the paper.

* http://arxiv.org/abs/1106.0313/
Relative locality: A deepening of the relativity principle
Giovanni Amelino-Camelia, Laurent Freidel, Jerzy Kowalski-Glikman, Lee Smolin

 

[RUTA]

Thanks, marcus. I was not aware of fluctuations defined per scale or position.

I read the paper and did not see the terms "fluctuates" or "fluctuating" after the intro. He talks about thermal time and proper time, both are embedded in spacetime, so there are no physical differences in spacetime geometry viewed in these temporal coordinates, as he's not abandoning general covariance. He must mean fluctuations in *spatial* geometry, as you suggest.

 

[julian]

Here's a hard core analysis of Rovelli, Connes paper: http://www.theorie.physik.uni-goettingen.de/forschung/qft/theses/dipl/Paetz.pdf

 

[FalseVaccum89]

Recently, I've been going back and forth between reading the popular account he wrote about his views on "timelessness" and his technical papers on the subject. From what I gather his views would be a near-perfect description of a truly discrete, quantized form of time, instead of one of true timelessness.

 

[inflector]

My take on Barbour's thinking is something different.

He's simply saying that what is fundamental is the flow of change. And that what we conceive of as time is simply periodicity in the flow of change. We detect this periodicity using repeating mechanisms or systems of various sorts: from pendulums swinging to revolution and rotation of planets like Earth to vibrations in crystals.

So it's more that the change is fundamental and that the periodicity in systems emerges when there are loops in the systems which cause the periodicity as change flows through and configurations repeat.

If one could imagine large-scale cellular automata was driving the universe like a big Conway's game of Life, and matter exists as persistent structures in that universe (like the gliders or toad and oscillators toads, pentadecathlons, queen bees in Life) , then there is nothing per-se that locks the timing of the steps. If a pause between steps happened to occur while the big computer running the simulation did something else, there would be no way to measure the pause or even know it happened since the only thing we can detect is the periodic repetitions of the oscillations.

So the real insight or change in perspective Barbour proposes is that change, not time is fundamental. This corresponds to a corresponding change perspective in physics from one that is state-based where one is concerned with changes in state, to one that is dynamics-based where one is concerned with the flow of change through the system and not the duration of any particular flows.

When seen through this lens, for example, even the fixed speed of light becomes easier to understand. The flow of change due to electromagnetic energy happens at a fixed interval we think of as a fixed speed because that flow itself is fundamental. And it is not time that changes during acceleration and under high gravity but the speed of the flow.

This way of thinking opens up some possible new ways for thinking about quantum gravity. For example, if space is quantized and the quanta are closer together under heavy gravity, and change is propagated across quanta, then the flow would appear to happen at a slower rate under relatively more gravity when compared to the flow with that is under less gravity because there would be more quanta over which the change would flow to exhibit the same periodicity. Now, I'm not saying this is what happens, only that this is a possibility that arises when one thinks of change as fundamental that would not so easily arise in one's mind when you think of time as fundamental.

 

[Lord Crc]

He's simply saying that what is fundamental is the flow of change. And that what we conceive of as time is simply periodicity in the flow of change.

Why the need for periodicity to establish a notion of time?

 

[julian]

You're saying `flow of change' is something that can not be further reduced, it is fundamental? It's something you just have to accept.

Rovelli talks about how a pendulum and a clock are both paramertarized by the ficticous parameter \tau, variation of \tau takes you through every pair of correlations. From this alone it is very difficult to understand change, just that there are different possible correlations.

 

[julian]

By the way, the link I gave earlier - http://www.theorie.physik.uni-goetti...dipl/Paetz.pdf - seems to look competent and comprehensive

 

[Meselwulf]

I could say a great deal on this subject... I might tomorrow.

 

[inflector]

Why the need for periodicity to establish a notion of time?

Without periodicity, one would not make the argument that something consistent is passing. Without periodicity, there is nothing against which to measure the passage of time. No clock ticks means no clock.

In Newton's world, time was thought to be continuous and unchanging because of the consistency of the periodicity of our clocks.

 

[inflector]

By the way, the link I gave earlier - [...] - seems to look competent and comprehensive

Yes, I concur.

 

[Meselwulf]

Without periodicity, one would not make the argument that something consistent is passing. Without periodicity, there is nothing against which to measure the passage of time. No clock ticks means no clock.

In Newton's world, time was thought to be continuous and unchanging because of the consistency of the periodicity of our clocks.

It's not even such that... I thinkI think the fact is, is that time is experienced by Bradydonic systems... anything before that which this which our universe arose from (i.e. radiation) has no effect on this world when time is concerned.

Time is only concerned by which can understand it, not that which travels at the speed of light which our universe was borne from. We are slow moving systems, experiencing time and anything before this is FAR more fundamental. Geometrogenesis, has a lot to say about this.

 

[julian]

Hi Meselwulf, you've lost me...what's a Bradydonic system? I think I have some understanding of what Geometrogenesis means though.

 

[FalseVaccum89]

This way of thinking opens up some possible new ways for thinking about quantum gravity. For example, if space is quantized and the quanta are closer together under heavy gravity, and change is propagated across quanta, then the flow would appear to happen at a slower rate under relatively more gravity when compared to the flow with that is under less gravity because there would be more quanta over which the change would flow to exhibit the same periodicity. Now, I'm not saying this is what happens, only that this is a possibility that arises when one thinks of change as fundamental that would not so easily arise in one's mind when you think of time as fundamental.

This is actually something I've been mulling over for the past few months! Glad to know I'm not the only one.

Anyway, I do have a question. Do you think the quanta of space would be finite in extent, or would they be infinitesimal? Because, I'm thinking if they're infinitesimal, one would still have the same problems with infinities in quantizing a continuous spacetime manifold.

An observation and question: Barbour makes a point in The End of Time of referring to "successive Nows" multiple times, as if each instant (which I would assume would correspond to the Planck time, though I'm not sure), is discrete. (Well, discrete physically, but tracing a continuous path in the configuration space of Platonia.) Wouldn't this amount to effectively a quantization of time? Or am I missing the point?

Thanks

-John

 

[Nano-Passion]

Things can be real but not fundamental--the example often given is the temperature of a system---the individual molecules do not have temperature so it is not fundamental at the microscope level of physical reality. But temperature emerges importantly at a collective level.

I can buy the idea that time is not fundamental, rather, it is an emergent property of the universe. It makes no sense, however, to question the obvious reality of time in the current universe. If it is an illusion, it is so extraordinarily clever it raises even more troubling questions than the ones it would resolve.

By definition, "real" or "reality" is an emergent property. I think what you meant to say is that it doesn't exist. Whatever is not fundamental is only real with respect to the observer, in other words it takes the conscious mind to argue that it is real. It is real with respect to the observer, but it does not exist (have an objective being), strictly speaking.

 

[DennisN]

George Ellis was Stephen Hawking's co-author of the classic book The Large Scale Structure of Space-Time back when Hawking was doing majorly important science. Ellis is what you'd call an expert on fundamental questions about time and space and he nixes the block spacetime and drives the point home with his trolleycar. As I recall that's a fun one too, at least the first few pages. I don't have the link though.

After reading this, I got interested in finding that trolleycar, and I think I did;
http://www.youtube.com/watch?v=qTmt3P05bIY (at 07:30, but he refers to a "massive object with two computer controlled rockets that move it right or left")

Pretty simple but powerful argument IMO. Fun, and thoughtful!

 

[Naty1]

Purely verbal description has a certain vagueness--the common-language meaning, i.e. the usage, "fluctuates" one might say So often, I imagine, one has read further into any given article to see mathematically what is intended.

Based on discussions, arguments, and so forth in these forums, I find it difficult to believe everyone agrees on mathematics either...whether a particular formulation is or is not appropriate in given circumstances, and if one seems appropriate, what it means.

I still find the 'Shut up and calculate.' description very useful to keep in mind ...from Feynman, I think!

 

[marcus]

George Ellis was Stephen Hawking's co-author of the classic book The Large Scale Structure of Space-Time back when Hawking was doing majorly important science. Ellis is what you'd call an expert on fundamental questions about time and space and he nixes the block spacetime and drives the point home with his trolleycar. As I recall that's a fun one too, at least the first few pages. I don't have the link though.

After reading this, I got interested in finding that trolleycar, and I think I did;
http://www.youtube.com/watch?v=qTmt3P05bIY (at 07:30, but he refers to a "massive object with two computer controlled rockets that move it right or left")

Pretty simple but powerful argument IMO. Fun, and thoughtful!

Thanks for tracking down the trolley! I'll check out the link you found for it, and am delighted someone else liked that argument against the standard block universe concept.

You might also like Ellis' prizewinning wide-audience essay "The Flow of Time" that is listed here:
http://fqxi.org/community/essay/winners/2008.1
along with a halfdozen other essays (Barbour, Rovelli, Kiefer, Carroll...)
Scroll down to where it says "second community prize" and there's a link.
I think I first encountered his trolley car example in this essay. And it may in fact not be a trolley car but some other massive object lurching erratically right and left under the control of a Schroedinger Cat driver.

 

[RUTA]

I still find the 'Shut up and calculate.' description very useful to keep in mind ...from Feynman, I think!

http://fisica.ciencias.uchile.cl/~emenendez/uploads/Cursos/callate-y-calcula.pdf

Here is an article by Mermin on the source of that quote. I, like Mermin, would like to whether Feynman is the true source.

 

[DennisN]

Thanks for tracking down the trolley! I'll check out the link you found for it, and am delighted someone else liked that argument against the standard block universe concept.

You might also like Ellis' prizewinning wide-audience essay "The Flow of Time" that is listed here:
http://fqxi.org/community/essay/winners/2008.1
along with a halfdozen other essays (Barbour, Rovelli, Kiefer, Carroll...)
Scroll down to where it says "second community prize" and there's a link.
I think I first encountered his trolley car example in this essay. And it may in fact not be a trolley car but some other massive object lurching erratically right and left under the control of a Schroedinger Cat driver.

Thanks, Marcus!
Yes, I liked it, I find Ellis' writing and arguments quite easy to follow (yes, you are correct, he refers to a massive object with rockets rather than a trolley). Direct link for others: On The Flow Of Time (George FR Ellis, pdf). The way I see it, Ellis delegates the question of time/arrow of time to the measurement problem and the unpredictability in quantum mechanics (probabilities can be computed, but the different outcomes can't be predicted). So, to me it would seem a block universalist would have to come up with some kind of deterministic "subquantum" theory to save the block universe...

I saw a couple of other clips from the FQXi "Setting Time Aright" conference which I share here:

Julian Barbour (clip)
(about Machian dynamics, shape space, motion and (emergent) time) - quite mindboggling, but I think I understand it at least in principle.

Tim Maudlin (clip)
(Maudlin describes a new mathematical tool set based on lines) - quite abstract, and I didn't see the entire clip.

George Ellis (clip) (mentioned before)
(about block universe versus evolving block universe, 2nd law of thermodynamics etc) - I enjoyed the entire clip, I think there were many thoughtful things. From 17:00 - 24:00 he talks about adaptive selection and describes some fun examples.Now, the question for me is:
Will I spend time reading some, all or none of the FXQi essays about time?

Quantum mechanics/Copenhagen interpretation says the decision is governed by a wavefunction which will collapse into one essay only. The wavefunction will then start to evolve again, and it might later collapse into some other essay.

The Many-worlds interpretation says there exists versions of me which already have read all of the essays. But I can't meet with those versions and discuss our impressions of the essays.

A block universalist might say I can't make a decision as the future is already present in some sense. But he/she seems unable to say how many essays that eventually will have been read by me .

Feynman might have said that I will browse all of the essays, and read the one which requires the least effort at that moment.

I don't know who's right, but I think I'm with CI/Feynman on this matter. I like to believe there is only one me, and that I at least have some influence on what I will read.

 

[ImaLooser]

http://fisica.ciencias.uchile.cl/~emenendez/uploads/Cursos/callate-y-calcula.pdf

Here is an article by Mermin on the source of that quote. I, like Mermin, would like to whether Feynman is the true source.

I feel certain that Feynman didn't say "shut up and calculate." It was the opposite of the way he thought. He was preoccupied with models and strongly opposed formalism.

What's more, he would never be so curt and brusque. It just isn't his style.

 

[experimentum]

Hello, I think what you are really asking is can time not exist if we don't want it to. Answer is no, time is not a result of thought. Thought does not change on a separate timeline of that of its relative spatial objects around it, the rate at witch thought happens remains constant just the total amount of time is comparitivly different. More true is saying thought is a result of time.

 

[experimentum]

Time is not a result of Thought, if I don't want time that won't make it go away and that's what you are really asking is time a result of thought. No, thought is a result of time and thought patterns are undistinguishable to the thinker even if the timeline is different only the total amount of time differs by comparison. Thus proving time and thought are a constant.

 

[marcus]

We've come quite a ways. I want to recap some of what was said on page 1 of this thread. Starting with Julian's post #1.
The gas in a box can be in equilibrium even though individual molecules are colliding and bouncing around. It depends on perspective. Micro-beings riding on the molecules can have a local idea of time based on motion of surrounding molecules. Their world doesn't look like it's in equilibrium to them, though it does to us. And also any thermal equilibrium state breaks Lorentz invariance and gives us an intrinsic macro idea of time This was what Rovelli was discussing as Julian pointed to in post #1. Here is the OP:

I prefer Rovelli's explanation of evolution from a timeless universe which has to do with how we have limited information about the world - less depressing perhaps as it leaves room for change? Like England winning the world cup.

...If you have a particularly clear passage by him where he explains that idea, I'd be glad for a pointer to it. Are you perhaps thinking of this recent paper?
4059419]http://arxiv.org/abs/1209.0065
General relativistic statistical mechanics
Carlo Rovelli
(Submitted on 1 Sep 2012)
Understanding thermodynamics and statistical mechanics in the full general relativistic context is an open problem. I give tentative definitions of equilibrium state, mean values, mean geometry, entropy and temperature, which reduce to the conventional ones in the non-relativistic limit, but remain valid for a general covariant theory. The formalism extends to quantum theory. The construction builds on the idea of thermal time, on a notion of locality for this time, and on the distinction between global and local temperature. The last is the temperature measured by a local thermometer, and is given by kT = [STRIKE]h[/STRIKE] dτ/ds, with k the Boltzmann constant, [STRIKE]h[/STRIKE] the Planck constant, ds proper time and dτ the equilibrium thermal time.
9 pages. A tentative second step in the thermal time direction, 10 years after the paper with Connes. The aim is the full thermodynamics of gravity. The language of the paper is a bit technical: look at the Appendix first

It is in Rovelli's paper "Forget time" http://arxiv.org/pdf/0903.3832.pdf he talks about it:

"The time of our experience is associated with a number of peculiar features that make it a very special physical variable. Intuitively (and imprecisely) speaking, time “flows”, we can never “go back in time”, we remember the past but not the future, and so on. Where do all these very peculiar features of the time variable come from?

I think that these features are not mechanical. Rather they emerge at the thermodynamical level. More precisely, these are all features that emerge when we give an approximate statistical description of a system with a large number of degrees of freedom. We represent our incomplete knowledge and assumptions in terms of a statistical state..."

Yes this is related to his new paper. After posting the Barbour's intro I came across Rovelli's new paper. Exciting to see if there is progress as I remember the paper he wrote with Connes http://arxiv.org/pdf/gr-qc/9406019.pdf and finding it very interesting but that was a while ago. I'm having a look at them both now...

This idea of a THERMODYNAMIC TIME arising from a global equilibrium state comes out of the Connes Rovelli paper which Julian gave a link to. There is also the idea of LOCAL time emergent from motions or mechanics but these are reversible. Barbour shows how time emerges from local motions. but that local emergence doesn't explain everything, e.g. direction. So there is an idea of scale. What level of time are we talking about? Also Naty gave an interesting reference to a paper that says a lot about the problem of understanding time.

...
Rovelli: Unfinished revolution
Introductive chapter of a book on Quantum Gravity

The link to this is http://arxiv.org/abs/gr-qc/0604045. And Chronos concisely summed things up at the end of page #1 of thread.

I can buy the idea that time is not fundamental, rather, it is an emergent property of the universe...

I want to add one idea to the discussion at this point. We have seen that time is "scale dependent"---it emerges from experience at different levels. Like temperature too. Temperature depends on at what scale you measure and it is emergent. It is very real! But it is emergent from more fundamental descriptors. Like Chronos said.

OK so time is emergent and scale dependent, now I want to add a footnote to that: The *expansion* of distances in the universe makes scale dependence very interesting. Geometry is dynamic you can have things staying in the same place but everything getting farther apart without any relative change in position.

Assuming the (LQC model) cosmological bounce---at the maximum energy density start of expansion, the universe was in thermal equilibrium. It was like the distribution of gas in a box, all flattened out under the regime of repellent gravitation (which is what causes bounce at extreme energy density in LQC model). So because GR is timeless (as therefore QGR must be also) the U is forever in equilibrium state.

So it has a thermal time, as Connes and Rovelli showed, which derives from any equilibrium state, its own global time. This is essentially the same as Friedmann universe time used by cosmologists, they get it by fitting data to model and calculating age of U, or they get it from CMB temperature. Same thing.

*But also expansion is like a zoom microscope* So compared with things at the start of expansion we are like the very small beings riding on the molecules in the box. So we see things around us that don't look like equilibrium. Stuff is happening. If you ran the whole show back to the start of expansion, it would look smooth and even, and it STILL IS in a sense if you adopt a cosmological perspective. But locally the individual molecules we are riding on are bucking and whirling splitting and merging.

Connes and Rovelli introduce the idea of a geometric temperature to coordinate these ideas of local and global time. It doesn't seem like a bad idea. Somebody named Tolman (at Oxford I think) had already discussed geometric temperature in the 1930s and C&R's idea turned out to recover Tolman's in the relevant case. So there is all this interesting stuff.

 

[marcus]

I guess two obvious things everybody realizes but could be mentioned:

Obviously the free energy in a situation depends on the scale you're able to manipulate. If you are molecule-size and live in a box of gas, then you can lasso molecules and can harness them (or play the Maxwell demon with them), and get energy. But whatever you do with the energy makes no difference to a large outsider. He looks in and sees no free energy---because he can't see or manipulate or benefit at your scale. He sees a uniform "temperature" throughout, which you do not. Whatever you accomplish with the free energy you see doesn't make a damn bit of difference to him---it still looks like gas in a box. So free energy depends on the scale at which the observer is interacting with it, and likewise the Boltzmann distribution, depending as it does on the free energy. So the idea of EQUILIBRIUM depends on scale.

The second obvious thing to mention, since we are concerned with cosmology, is that cosmologists have coordinates called COMOVING coordinates where the separation between things does not change. Aside from little random individual jiggles, as thing's comoving coordinates do not change. Not substantially compared with the expansion process itself. So two hydrogen atoms are about as far apart now, in comov. dist., as they were when the universe was only a few years old. things do fall together and interact and recombine and split apart etc but that is a small percentage of their comoving distance from each other, which stays approximately constant.
So I suppose some of the analysis of the sort of things we were talking about could be done using comoving coordinates.

Interestingly, it seem if we imagine doing relativistic thermodynamics in a quantum cosmology context it might happen that the U is, and always has been, in a PURE STATE and that it also (at a certain scale) is in a state of THERMAL EQUILIBRIUM.
=================

The reason it's relevant is that several of us in the thread seem to agree on looking at time as real but *emergent* either from local motions or thermodynamics. In particular e.g. Julian Barbour in his prize-winning FQXi essay showed clearly how time is emergent from local motions, at a certain level. One does not have to treat it as a quasi-spatial "extra" dimension. One wants to be able to generalize on both Barbour's time and thermodynamic or "thermal" time (which may, at root, be the same thing as Barbour's) to understand the emergence of time in a variety of contexts and at various scales.

 

[Paulibus]

Marcus: Your recent post #57 said things that really needed saying. I liked it a lot. Here are a few comments.

As Niels Bohr pointed out, Physics is a matter of what we say about stuff, not what stuff “is”. This justifies the use of inverted commas (here) and prolifically in your post, together with stars and upper case to distinguish words ( e.g.: is, emergent, temperature, equilibrium) that have context-sensitive meanings. To be trite; '"Obviously” physics just describes what we call reality. This description is perforce made in the context of common human experience, say of hot and cold, or the maintenance of a status quo. When we try to extend such descriptions beyond scales familiar to us, a qualification as “emergent” can be useful for broadening context. So is the quantitative and logical extension provided to ordinary language by mathematics.

But let’s not kid ourselves that the words and mathematical descriptions we use have absolute eternal meanings; they just conveniently communicate concepts between us. Like the mysterious word “time” that everybody knows. Although we cannot yet claim to accurately understand and describe time, one thing does stand out: using time as a parameter to characterise change works wherever physics rules. This, it seems, is all over the Universe. Therefore: time can’t just be some local quirky emergent thing; it must be related to something universal, like the observed red-shift and its cause, namely “expansion”. Or is this also just an "emergent" aspect of the “reality” that we try to describe?

 

[ImaLooser]

Or is this also just an "emergent" aspect of the “reality” that we try to describe?

Emergent is rapidly becoming one of my less favorite words. It seems like a classy way to say I dunno.

 

[experimentum]

I guess two obvious things everybody realizes but could be mentioned:

Obviously the free energy in a situation depends on the scale you're able to manipulate. If you are molecule-size and live in a box of gas, then you can lasso molecules and can harness them (or play the Maxwell demon with them), and get energy. But whatever you do with the energy makes no difference to a large outsider. He looks in and sees no free energy---because he can't see or manipulate or benefit at your scale. He sees a uniform "temperature" throughout, which you do not. Whatever you accomplish with the free energy you see doesn't make a damn bit of difference to him---it still looks like gas in a box. So free energy depends on the scale at which the observer is interacting with it, and likewise the Boltzmann distribution, depending as it does on the free energy. So the idea of EQUILIBRIUM depends on scale.

The second obvious thing to mention, since we are concerned with cosmology, is that cosmologists have coordinates called COMOVING coordinates where the separation between things does not change. Aside from little random individual jiggles, as thing's comoving coordinates do not change. Not substantially compared with the expansion process itself. So two hydrogen atoms are about as far apart now, in comov. dist., as they were when the universe was only a few years old. things do fall together and interact and recombine and split apart etc but that is a small percentage of their comoving distance from each other, which stays approximately constant.
So I suppose some of the analysis of the sort of things we were talking about could be done using comoving coordinates.

Interestingly, it seem if we imagine doing relativistic thermodynamics in a quantum cosmology context it might happen that the U is, and always has been, in a PURE STATE and that it also (at a certain scale) is in a state of THERMAL EQUILIBRIUM.
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The reason it's relevant is that several of us in the thread seem to agree on looking at time as real but *emergent* either from local motions or thermodynamics. In particular e.g. Julian Barbour in his prize-winning FQXi essay showed clearly how time is emergent from local motions, at a certain level. One does not have to treat it as a quasi-spatial "extra" dimension. One wants to be able to generalize on both Barbour's time and thermodynamic or "thermal" time (which may, at root, be the same thing as Barbour's) to understand the emergence of time in a variety of contexts and at various scales.

I can't even begin to understand everything in these posts. My math and even my vocabulary skills being well below the required level but I try because i still learn from the bits and peices I do pick up.
Theoretical physics I relize is very advanced even among the real physicists but let me check if I somewhat understand this.

I'm understanding it as the current laws for time are universal in this model the box is our 'universe' the gas filling the box is 'time' and any events it real time are represented as a temperature change so the model has a way of catagorizing integral parts of time us being assumedly on the hotter end of the scale. Is this right that I'm sub catagorizing us given any present moment in our timelines is not assumed but analitical. In my mind this gives us a convective effect on the gas.

I hope I'm getting it because if not its a real blow to my ego well, either way it kinda is cause I never would have bien able to come up with that myself :( and, I've just wasted everyones time! but hey, wait a minute, don't be such a hothead! lol!