From time to timescape – Einstein’s unfinished revolution?

[Garth]

In today's Physics ArXiv:

FROM TIME TO TIMESCAPE – EINSTEIN’S UNFINISHED REVOLUTION

Dark Energy as simply a mis-identification of gravitational energy gradients and the resulting variance in clock rates?

David Wiltshire's Abstract:

I argue that Einstein overlooked an important aspect of the relativity of time in never quite realizing his quest to embody Mach’s principle in his theory of gravity. As a step towards that goal, I broaden the Strong Equivalence Principle to a new principle of physics, the Cosmological Equivalence Principle, to account for the role of the evolving average regional density of the universe in the synchronisation of clocks and the relative calibration of inertial frames. In a universe dominated by voids of the size observed in large-scale structure surveys, the density contrasts of expanding regions are strong enough that a relative deceleration of the background between voids and the environmentof galaxies, typically of order 10⁻¹⁰ms⁻², must be accounted for. As a result one finds a universe whose present age varies by billions of years according to the position of the observer: a timescape. This model universe is observationally viable: it passes three critical independent tests, and makes additional predictions. Dark energy is revealed as a mis-identification of gravitational energy gradients and the resulting variance in clock rates. Understanding the biggest mystery in cosmology therefore involves a paradigm shift, but in an unexpected direction: the conceptual understanding of time and energy in Einstein’s own theory is incomplete.

Garth

 

[oldman]

In today's Physics ArXiv:

FROM TIME TO TIMESCAPE – EINSTEIN’S UNFINISHED REVOLUTION

Dark Energy as simply a mis-identification of gravitational energy gradients and the resulting variance in clock rates?

Garth

A fox among the Christmas Turkeys, indeed --- if it were true. Perhaps it is. I'm not competent to judge. But Wiltshire's claim that differently situated observers would assign widely different ages to the universe has an echo even in special relativity, which teaches us that there is no absolute measure of duration or absolute notion of simultaneity or concept of "now'.

Just imagine not a twin paradox, but say a multiplet paradox, in which many siblings follow very different worldlines through spacetime before reuniting for Christmas festivities. They would then have different physical ages, despite their common origin. There is no such thing as a universally experienced measure of age --- unless it is one's wrinkle count.

If Wiltshire is correct, would observers differently situated in the universe (say void dwellers and galaxy dwellers) nevertheless all measure the same Z for the Cosmic Microwave Background? and if so, would their assignment of a common age to the universe using a common scheme (say the Lambda CDM model) then be as misleading as the assignment by members of the the multiplet siblings of a common age to them, despite their diversity of wrinkle counts? Wiltshire's arguments suggest to me that the answer might be "yes".

 

[Garth]

First it seems you have misunderstood the twin paradox.

The paradox is not that the twins on meeting up find they have different ages, as you seem to suggest, but that each might think that it is they who are the eldest.

The paradox in SR is resolved by determining which of the twins had not been on an inertial trajectory through space-time. It is that twin uniquely who would be of the younger age.

Garth

 

[oldman]

First it seems you have misunderstood the twin paradox.

The paradox is not that the twins on meeting up find they have different ages, as you seem to suggest, but that each might think that it is they who are the eldest.

The paradox in SR is resolved by determining which of the twins had not been on an inertial trajectory through space-time. It is that twin uniquely who would be of the younger age.

Garth

I suspect you are considering the particular, instead of the general case --- but I'm not sure. Perhaps you could elaborate a bit more? I'm under the impression that observer-measured durations and their differences depend in general on the integrated proper time that elapses along any closed loop of worldline followed by an observer, not just on who follows a non-inertial path and who doesn't. Is it the sign of the difference, rather than its magnitude that you are talking about?

 

[George Jones]

I'm under the impression that observer-measured durations and their differences depend in general on the integrated proper time that elapses along any closed loop of worldline followed by an observer, not just on who follows a non-inertial path and who doesn't.

Let A and B timelike related events with B in the future of A.

Special relativity. Of all the observer worldlines running from A to B, the worldline of the unique intertial observer who experiences both A and B has the greatest integrated proper time.

General relativity. There is not necessarily a unique inertial (freely falling) worldline joining A and B, and it is possible for the integrated proper time of an accelerated observer who experiences A and B to be greater than the integrated proper time of an inertial observer who experiences A and B. See

https://www.physicsforums.com/showthread.php?p=1836071#post1836071.

I started this post with

In this post, I will summarize the results, and the I will gives an explanation of the results in another post.

and I wrote recently in another related post

Either tonight or tomorrow, I'll post (some of) the fairly simple details of a GR example for which the usual SR result doesn't hold, i.e., the elapsed proper time between meetings for an accelerated clock is greater than for a non-accelerated (geodesic) clock.

The example consists of two clocks that have same $r$, with one clock in geodesic circular orbit (freely falling with no acceleration) and one clock hovering (accelerated).

but I have not written these promised posts.

I haven't read Wiltshire's paper (I hope to read it soon.), but I don't think these counter-intuitive GR results play a role.

 

[Ich]

Sorry, if I read

...Einstein overlooked an important aspect...
...new principle of physics...
...paradigm shift...
...the conceptual understanding of time and energy in Einstein’s own theory is incomplete... ,

I've had enough.
Wiltshire may or may not have a point, he won't get (me as) an audience as long as he's earning ~30 crackpot points in the abstract alone.

 

[oldman]

Let A and B timelike related events with B in the future of A.

Special relativity. Of all the observer worldlines running from A to B, the worldline of the unique intertial observer who experiences both A and B has the greatest integrated proper time.

General relativity. There is not necessarily a unique inertial (freely falling) worldline joining A and B, and it is possible for the integrated proper time of an accelerated observer who experiences A and B to be greater than the integrated proper time of an inertial observer who experiences A and B. See

https://www.physicsforums.com/showthread.php?p=1836071#post1836071.

Thanks, George. Your statement in the earlier post you refer to here, namely:

...there is no reason to expect elapsed proper times to be the same between coincidence events for geosecics that pass through different events between the coincidence events...

is a further clarification of my impression that:

...observer-measured durations (between coincidence events)and their differences depend in general on the integrated proper time(s) that elapses along ... worldline(s) followed by ... observer (s), not just on who follows a non-inertial path and who doesn't.

. Time is indeed strange, and it seems to me that Wiltshire's further (i.e. beyond Einstein's) exploration of this strangeness is worth undertaking. Whether he is correct or not is another matter...

 

[apeiron]

I've had enough.
Wiltshire may or may not have a point, he won't get (me as) an audience as long as he's earning ~30 crackpot points in the abstract alone.

He's not a crackpot. He's a former student of Hawking and well respected. I heard him give his first paper about five years ago and the latest version just the other week. This year he has finally been getting a lot of traction - plenary in Paris, etc.

It may still be a wrong explanation. Dark energy may be true. But occam's razor says the simpler case must be ruled out. And Wiltshire is now getting to the level of calculation where things look testable.

 

[twofish-quant]

He's not a crackpot. He's a former student of Hawking and well respected. I heard him give his first paper about five years ago and the latest version just the other week. This year he has finally been getting a lot of traction - plenary in Paris, etc.

That doesn't disqualify him from being a crackpot. One reason that I have a lot of tolerance to amateur crackpots is that I've learned to tolerate the huge number of professional crackpots in the field.

On the other hand, being a crackpot isn't necessarily a bad thing. The only difference between a genius and a lunatic is that the genius can turn off the voices when he needs to.

 

[apeiron]

The only difference between a genius and a lunatic is that the genius can turn off the voices when he needs to.

Erm, any references to support that? It's not really fair to either geniuses or lunatics, even if you say it in jest.

Personally, I think Wiltshire is doing a clever thing. And of course I am influenced by spending time with him to find out what he is about.

He started off responding to dark energy. He realized it might be just observational error due to our local frame of reference being possible underdense.

Then regardless of whether this is true or not, he has moved on to a more general issue. The fact that GR cosmology has made a simplifying assumption about the metric, that everything is flat, smooth, homogeneous, isotropic, and is not thus an accurate model of the reality.

As he says...

There is a dilemma that any
spacetime split inevitably breaks a given particle motion into a motion of the background
and a motion with respect to the background; and this may involve a degree
of arbitrariness.

So you have a relativistic background in which there is no average frame of reference in fact. Even the CMB probably doesn't give you a universal measure of time.

So how do you do the calculations for the equation of state if there is a basic lumpiness to things that creates a cosmic froth of relativistic effect curving the background itself?

Wiltshire was saying this lumpiness is suggested by observational evidence of fractal matter distribution, which in turn is a likely result of the sound horizon in early big bang. This is fairly recent motivation for actually moving the calculations to another level of relativistic precision.

I asked him why it hadn't been done already. He said just because the calculations are really, really, difficult. You would have to have a lot of motivation to take the project on. He has had to take the project on because people pointed out the lack of full-working out in his early papers.

As usual, genius is in fact 90% perspiration. And cranks are the people who don't learn from their critics.

 

[marcus]

He's not a crackpot. He's a former student of Hawking and well respected...

What I recall (correct me if I am wrong) is that Gary Gibbons was a PhD student of Hawking and that Wiltshire had Gibbons for advisor. Which doesn't contradict what you said. Just that in terms of PhD advisor, Wiltshire is Hawking's "grand-student".

I remember reading Wiltshire's early papers about an alternative explanation of accelerated expansion---coming from largescale unevenness in density. Back in 2005 or so, I think.
I've always thought of his line as worth pursuing, but so far not convincing and not (yet at least) appropriate to make a big fuss about.

Kea, a PF member who posted a lot here in around 2005-2006, had a high opinion of Wiltshire. She was a kiwi PhD student/postdoc.

I think twofish was (as you suspected) speaking in jest. Jovial jesting like that is hard to balance so that it is perfectly fair. I thought what he said was pretty funny, enjoyed it, although I completely disagree with the characterization "crackpot"

 

[marcus]

... Even the CMB probably doesn't give you a universal measure of time.
...

That is quite true. Universe time is only approximately definable, inasmuch as the FRW model fits (which it doesn't, exactly).

Time is a delicious mystery.

By coincidence it was Carlo Rovelli (back in 2003) who pointed out to me that we have no universal measure of time. He said something like "what about people deep in massive galaxies" compared with other people in less dense places. He asked if I could see how to put all those times together to get a universal standard time. A gentle guy and a good teacher.

I think we have to agree with a lot of what David Wiltshire says. (And respect his courage for pursuing a longshot.)

But I don't think we have to deny the existence of a positive cosmological constant, or the practical value of the CMB as a reference, or the remote (as yet unrealized) possibility of defining a universal time. We may yet know and understand so much more than we do today.

 

[twofish-quant]

Erm, any references to support that? It's not really fair to either geniuses or lunatics, even if you say it in jest.

Personal experience. Every theorist that I know (including myself) has some crazy, insane, long shot idea that they secretly think is the key to understanding the universe. The difference between productive physicists and the less productive one's, is that the more productive ones will keep the craziness under control, share their really weird ideas over drinks, but refrain from publishing papers in which you announce that you've solved the mysteries of the universe. From time to time, a theoretical physicist will lose it and either formally or informally say "YOU ARE ALL IDIOTS! I KNOW WHAT IS GOING ON HERE!" That usually doesn't provoke a good reaction (even if from time to time it happens to be true).

The other thing is that just like there is a very strong correlation between bipolar disorder and novelists, the number of theoretical physicists that are under treatment for some mental condition or have some close family member who is, seems to be much larger than the general population. What I mean by "being able to turn off the voices" is that there is the "I HAVE FOUND THE SECRET OF THE UNIVERSE" part of doing theoretical physics, and then then "well... maybe not..." part. People that end up being productive are able to do the second phase.

Then regardless of whether this is true or not, he has moved on to a more general issue. The fact that GR cosmology has made a simplifying assumption about the metric, that everything is flat, smooth, homogeneous, isotropic, and is not thus an accurate model of the reality.

Which is quite widely realized.

So how do you do the calculations for the equation of state if there is a basic lumpiness to things that creates a cosmic froth of relativistic effect curving the background itself?

You do a back of the envelope calculation that argues that GR effects aren't going to be that huge in calculating the EOS.

Also GR calculations *are* hard to do. There is a community of people that believes that redshifts are completely due to tired light and GR effects and those people *are* considered crackpots by most observational cosmologists. One thing that Wiltshire has to be careful is to not get lumped in with that group of people unless he really has some smoking gun.

One thing that can happen is that one professional crackpot can discredit an entire field of inquiry in which case things get thrown out that shouldn't be. Using GR symmetry arguments to propose basic changes in interpreting cosmological data gets you close enough so you have to be a little worried about how to phrase your papers.

 

[twofish-quant]

The thing that I'm interested in is whether Whitshire is proposing that general relativity as currently used in the standard model is wrong. If he is then it should be possible to take his proposed extensions to GR and then back translate them into an f(R) model in much the same way that the 3+1 membrane paradigm allows you to apply Newtonian dynamics to black hole accretion disk models, and I *think* that Whitshire is basically doing the same thing.

 

[Ich]

He's not a crackpot.

Just for the record: I didn't say that he is a crackpot. I just said that I'm not going to read a paper with "paradigm shift" and "Einstein wrong" in the abstract.
If there will really be a paradigm shift, it will come with a paper called "On a Heuristic Point of View Concerning the Production and Transformation of Light" or similar. Not everyone can afford understatement, I'll have a look at those who can.

 

[apeiron]

Just for the record: I didn't say that he is a crackpot. I just said that I'm not going to read a paper with "paradigm shift" and "Einstein wrong" in the abstract.

Yeah, next thing you know he will be talking about discovering "the mind of God".

But perhaps if you stopped at the abstract, you missed the note that puts things in a little more context.

This essay was a runner–up in the community awards for the 2008 FQXi Essay Contest on “the Nature of Time”.

 

[oldman]

Dark Energy as simply a mis-identification of gravitational energy gradients and the resulting variance in clock rates?

What about an informed answer to this question, instead of discussions of Wiltshire's scientific status?

It's not as if dark energy is such a well understood and experimentally confirmed part of physics as to preclude further suggestions!

 

[edpell]

The only difference between a genius and a lunatic is that the genius can turn off the voices when he needs to.

I would say the only difference between a genius and a lunatic is that eventually everyone agrees with the genius.

The fear and hatred that people express towards the non-canonical is just as high as the Catholic Churches fear and hate of Galileo. I think we have discovered a truth about human nature. People hate new ideas.

 

[edpell]

Or more generally there are two kinds of physicists 1) those whose status and self worth is tied to their mastery of an existing canon of theory and experimental data and who feel threatened by their current view being called into question and 2) those who enjoy learning and discovery and ideas (Ars Gratia Artis) an example would be Feynman.

Yes there are plenty of crazy people with crazy ideas that we could waste our whole lives reading and so we must try to filter the garbage from the gems. But the hate is a psychological problem of the hater. If you have some rational for filtering something tell me about it but I have no interest in hearing your hate or using your hate as a filter.

 

[apeiron]

What about an informed answer to this question, instead of discussions of Wiltshire's scientific status?

I second that motion.

I think we can accept Wiltshire is a credible academic. I've met enough geniuses and madmen to tell the difference. I wouldn't describe Wiltshire as either. But he seems to be doing exactly the kind of thing science is suppose to do - looking at the simpler explanation for surprising findings.

 

[twofish-quant]

I think we can accept Wiltshire is a credible academic. I've met enough geniuses and madmen to tell the difference. I wouldn't describe Wiltshire as either. But he seems to be doing exactly the kind of thing science is suppose to do - looking at the simpler explanation for surprising findings.

Same here. The paper he wrote was interesting. Did seem to be a lot of hand waving.

The big problem that I see with invoking gradients for dark energy is that it does seem to be to require new physics and the new physics would seem to me to have made its presence known around accretion disks. Also how to get Newtonian physics to work in a general relativistic context is something of a known problem.

 

[twofish-quant]

The other problem that I see is that just looking at the metric, I *think* it just reduces to a f(R) model and if you take the Newtonian limit you end up with a MOND model. However I think it does get rid of one problem with those types of models which is the composition problem. If you have weird things happen with galactic masses then why don't weird things happen when you have larger gradients with small masses (answer: things are reacting to the mean field).

Also one thing that Wilshire points out that is true is that in GR, there is no real global time, and so setting the time variable is arbitrary, but you end up choosing a metric to make the calculations easier.

 

[apeiron]

The big problem that I see with invoking gradients for dark energy is that it does seem to be to require new physics and the new physics would seem to me to have made its presence known around accretion disks. Also how to get Newtonian physics to work in a general relativistic context is something of a known problem.

I don't get any of this. Wiltshire is arguing that dark energy does not necessarily exist. It could just be an illusion created by the way we have to look through a whole lot of lumpy spacetimes, a soup of quasi-local Hubble flows.

It is not an argument for new physics but more careful GR calculations.

 

[apeiron]

If you have weird things happen with galactic masses then why don't weird things happen when you have larger gradients with small masses (answer: things are reacting to the mean field).

Also one thing that Wilshire points out that is true is that in GR, there is no real global time, and so setting the time variable is arbitrary, but you end up choosing a metric to make the calculations easier.

I am not an expert in GR, but what I heard was that most people have been doing the calculations the simple way - assuming a flat average FRW universe and then adding a sprinkle of relativistic inhomogeneities to account for galactic walls, filaments, and other observables at redshift scales greater than one.

Wiltshire says the proper way to do it is first model the relativistic inhomogeneities, then do your average to find out the "real" Hubble flow, the "real" age of the universe.

Again, I could be misdescribing. But it seemed agreed in the room that doing the averaging afterwards is the more correct way to apply GR to cosmology.

 

[twofish-quant]

I don't get any of this. Wiltshire is arguing that dark energy does not necessarily exist. It could just be an illusion created by the way we have to look through a whole lot of lumpy spacetimes, a soup of quasi-local Hubble flows.

Part of the problem with the paper was that it wasn't clear whether or not he was arguing for new physics or not, and after the third time I read through it carefully, I came to the conclusion that he *was* arguing for a non-standard theory of gravity.

It is not an argument for new physics but more careful GR calculations.

That's the big problem with the paper was that it wasn't clear whether it was arguing for more careful calculations or that gravity acts in a different way. After looking at the metric and thinking about it, my conclusion was that Wiltshire is arguing that general relativity is incorrect and that you need a mass dependent metric based on a new equivalence principle.

 

[edpell]

To quote from Wiltshire's paper "In laying the foundations of general relativity, Einstein sought to refine our physical understanding of that most central physical concept: inertia. As he stated: “In a consistent theory of relativity there can be be no inertia relatively to ‘space’, but only an inertia of masses relatively to one another”. This is the general philosophy that underlies Mach’s principle, which strongly guided Einstein."

When I put up a post mentioning Mach's principle it was deleted as "personal theory". I guess my question is why is this whole thread not deleted as "personal theory"? Or is truth defined by having a tenured professorship?

 

[George Jones]

To quote from Wiltshire's paper "In laying the foundations of general relativity, Einstein sought to refine our physical understanding of that most central physical concept: inertia. As he stated: “In a consistent theory of relativity there can be be no inertia relatively to ‘space’, but only an inertia of masses relatively to one another”. This is the general philosophy that underlies Mach’s principle, which strongly guided Einstein."

When I put up a post mentioning Mach's principle it was deleted as "personal theory". I guess my question is why is this whole thread not deleted as "personal theory"? Or is truth defined by having a tenured professorship?

As you have been told, Physics Forums rules, to which you agreed when you registered,

https://www.physicsforums.com/showthread.php?t=5374,

in part, state

Overly Speculative Posts: One of the main goals of PF is to help students learn the current status of physics as practiced by the scientific community; accordingly, Physicsforums.com strives to maintain high standards of academic integrity. There are many open questions in physics, and we welcome discussion on those subjects provided the discussion remains intellectually sound. It is against our Posting Guidelines to discuss, in most of the PF forums, new or non-mainstream theories or ideas that have not been published in professional peer-reviewed journals or are not part of current professional mainstream scientific discussion.

David Wiltshire has published his work in reputable physics journals like, for example, Physical Review D,

http://arxiv.org/abs/0909.0749.

 

[edpell]

OK "published in professional peer-reviewed journals" is the gold standard. So Wiltshire meets the standard so why are not the posts calling him a crackpot deleted?

 

[twofish-quant]

I am not an expert in GR, but what I heard was that most people have been doing the calculations the simple way - assuming a flat average FRW universe and then adding a sprinkle of relativistic inhomogeneities to account for galactic walls, filaments, and other observables at redshift scales greater than one.

I'm also not an expert in GR, but I've done GR in the context of neutron star calculation. What you do in this situation which is nicely explained by Van Riper (1979) is to start with a global clock, and then you use an integral to calculate the difference between the local reference frame and the global reference frame to take into account the difference in volumes and times. The nice thing about doing this is that if you do the integrals and you find that it doesn't make much of a difference, then you can forget about GR.

It's called the 3+1 formalism and there is a more sophisticated version of this in the book the membrane paradigm. The reason for all of this is to precisely to use Newtonian gas and EM physics in a correct GR calculation. The integrals aren't hard to do, and my gut feeling is that it's going to show that you can use Newtonian gas dynamics in a GR setting. I'd be shocked if people that ran large scale simulations of the universe didn't do this calculation first.

One reason that makes me pretty sure that Whitshire is invoking new physics is that if he weren't, he could do that integral and show that GR makes a difference at small scales and you can't do the problem with Newtonian gas dynamics in a 3+1 formalism. If that's what he was arguing, I'd expect to see a much different paper.

Wiltshire says the proper way to do it is first model the relativistic inhomogeneities, then do your average to find out the "real" Hubble flow, the "real" age of the universe.

But in order to make a difference, I think you'd have to invoke new physics in which the inhomogeneities make more of a difference than it would in standard GR.

Again, I could be misdescribing. But it seemed agreed in the room that doing the averaging afterwards is the more correct way to apply GR to cosmology.

The problem is that you make the problem harder without adding anything new. What people do in large scale cosmology simulations is to *assert* the existence of a global clock (which you can do since you have the freedom to choose your own coordinate system), and then model inhomogenities as deviations from the global clock. The global clock is just a choice of coordinate systems, and you just choose which whatever makes the calculations the easiest, and it turns out that if you run the numbers that the deviation from standard GR doesn't make that much difference so you can pretty much ignore them in your calculations.

Now what I think Wiltshire is saying is that if you create a metric so that the the inhomogenities have more of an impact on the clocks than standard GR implies that you can have acceleration without dark energy. I think he is right, but he is invoking new physics, and so he spends the first several pages of the paper coming up with a justification of the new physics. It is interesting because it's original new physics, but it's less interesting because it is new non-standard physics.

The final reason I'm pretty sure that Wiltshire *is* invoking new physics is that he doesn't do any detailed calculations. If he *were* saying that inhomogenities are being handled incorrectly, then it wouldn't be hard to do a "we have a problem" calculation using standard GR. What I think he is doing is to use a new equivalence principle to create a new *class* of models, but since you have a class of parameterizible models rather than a single model, the next step is to try to put numbers in that let you do calculations.

 

[twofish-quant]

OK "published in professional peer-reviewed journals" is the gold standard.

For some people, it is. Not for me, since I can think of some papers in Ap.J. that I (and pretty much everyone in the field) think are crackpot. I know of people in the National Academy of Sciences and who have Nobel prizes that have ideas that pretty much everyone in the field thinks are crackpot (i.e. don't mention topic black holes or accretion jets or redshift around so and so since he'll bore you with his "proof" that they don't exist).

So Wiltshire meets the standard so why are not the posts calling him a crackpot deleted?

Because sometimes calling someone a crackpot is a compliment. It's rather interesting looking at a "professional crackpot" because you can see how some of the personality characteristics make them obsessive about weird ideas that happen to be right, also make them obsessive about weird ideas that everyone else thinks are crazy.

Also professional crackpots sometimes win. There is one crazy idea which the first time it was explained to me, my reaction was that "well so and so has finally lost it". Over the last several years, it turns out I've gotten used to that idea, and I think it's pretty brilliant.

 

[twofish-quant]

When I put up a post mentioning Mach's principle it was deleted as "personal theory". I guess my question is why is this whole thread not deleted as "personal theory"? Or is truth defined by having a tenured professorship?

It's because he is playing the game and there's enough meat in the paper so that people in the field have something to think about. What he is suggesting is new and original, and it's fun to read new and original ideas even if they happen to be wrong.

 

[apeiron]

Part of the problem with the paper was that it wasn't clear whether or not he was arguing for new physics or not, and after the third time I read through it carefully, I came to the conclusion that he *was* arguing for a non-standard theory of gravity.

I'm still really surprised that this is your interpretation so it would be nice to hear if others see the same.

As I say, I had a good half hour conversation with Wiltshire and I think his belief is that he is doing GR more deeply - yes, a valid extension of the equivalence principle - rather than something which is new physics in the sense that anything was wrong or needs correcting at the equations level.

Making a probably non-standard suggestion myself, there is an interesting question when it comes to averaging over any system, but especially an open or expanding system.

In a closed or static system, we would expect averages to be gaussian. But in open or expanding systems, we expect averages to be log/log or powerlaw.

So I guess there is the possibility that the standard way of averaging the flatness of the universe builds on that gaussian expectation. And perhaps the reality may be fractal in some real sense. So for example, we might have relativistic curvature of quasi-localities over all scales. Mostly, we look at the universe as being large and flat. But around black-holes, clearly the curvature becomes extreme.

So if we could actually profile the average relativistic curvature of the timescape, it could perhaps be not generally "very flat" with a few local exceptions like black holes, but instead flat in a powerlaw sense.

I'm sure I will be told I'm wrong here. But I put it forward to be educated as to how I should be thinking about this. The timescape seems to say the universe is lumpy and so has local variations in spacetime curvature. But it could even be lumpy in a powerlaw fashion.

This connects with another long-running cosmo debate I could never follow - the apparent upset caused by fractal universe stories. All the debate about galactic walls, filaments, etc, and how large-scale cosmic structure would be a problem for the assumption of homogeneity, isotropy, what have you.

Wiltshire was certainly saying that it appears the universe is void dominated over 200 megaparsecs. And that would fit in with the sound horizon of the big bang. Below that scale, the variation would have been scrambled and look close to gaussian (which would of course mean that the universe would not actually fit a pure powerlaw matter/curvature distribution over all scales).

 

[edpell]

To quote Wiltshire from the peer reviewed literature "In laying the foundations of general relativity, Einstein sought to refine our physical understanding of that most central physical concept: inertia. As he stated: “In a consistent theory of relativity there can be be no inertia relatively to ‘space’, but only an inertia of masses relatively to one another”. This is the general philosophy that underlies Mach’s principle, which strongly guided Einstein."

How do we feel about this idea that inertia is defined only relative to other masses? Did Einstein think that? Does Wiltshire think that? Do you agree?

 

[George Jones]

For some people, it is.

But edpell did not ask about "some people," he asked about the policies of Physics Forums.

Not for me, since I can think of some papers in Ap.J. that I (and pretty much everyone in the field) think are crackpot. I know of people in the National Academy of Sciences and who have Nobel prizes that have ideas that pretty much everyone in the field thinks are crackpot (i.e. don't mention topic black holes or accretion jets or redshift around so and so since he'll bore you with his "proof" that they don't exist).

Yes, there are many examples of stuff like this, which is why Physics Forums Rules require more than just "published in professional peer-reviewed journals." For my take on the wording (which I think is overly convoluted) of the relevant part of Physics Forums Rules, see

https://www.physicsforums.com/showthread.php?p=2251832#post2251832.

This is a judgment call by the Mentors (moderators).

 

[Phrak]

dispit the crackpot points, most very irritating, i think it's worth the time to read it.