Radical new take on *uni*verse questions by Smolin, could be important

[marcus]

...4. In one of the Sci-Am article about Loop Quantum Gravity. It is said if different wavelength photons from far away in space are measured to arrive differently, it can support the discreteness of space. Isn't it this experiment has been done already? Is the result null or non-null?
...

Whatever was said in popular media doesn't matter. LQG was shown to be Lorentz covariant in a technical paper by Rovelli&Speziale in around 2009.
It was never proven rigorously that LQG predicts different arrival times (dispersion). So if they ever observe energydependent speed of light this will, unfortunatelyNOT support Loop or spin foam gravity. There was speculation that Loop might imply dispersion up to around 2006 but then people tried very hard to prove it mathematically and failed. So there is this free-floating popular misconception...

3. Does Loop Quantum Gravity use the principle of Shape Dynamics or are they independent GR theories?

There are several versions of Loop gravity being worked on by the community. SD people including Barbour and Koslowski were all over the opening day program of Loops 2011 at Madrid. They had a less prominent role at the next Loops conference. I have seen papers by SD people about what SD can give Loop, what can be put in, how to do SD in a Loop way etc etc. Loop people have a lot of experience QUANTIZING theory of spacetime geometry. And SD is still basically a classical theory--it still has not gotten very far in the quantum direction. So SD people get invited to present and Loop people listen and there is room for collaboration.

But if you want my private opinion I think SD was to some extent a FAD, which peaked around 2011. I see diminished activity. IT HAS THINGS TO TELL US though. So you should notice what I said about the ILQGS talk by Koslowski on November 12, in about one week from now. It is basically about "What can Loop learn from SD?" This is the online International LQG Seminar hookup, like a big conference call with various places in US Canada Europe. Listen to the presentation, the questions, the answers, the discussion. If the connection is good and everybody joins in you can get a feel for how it is going with SD.

The short answer is that Loop is several things and they are separate from SD. Loop has about 10 times the research activity and might eventually cannibalize SD---we can't tell the future of research, it is almost by definition impossible to predict the future evolution of human understanding. Anything can happen. BTW Loop has its own "in house" study of global time called "Tomita Time" or "thermal time hypothesis". We've had thread about that. My feeling is that it is more interesting than SD, but also in preliminary growth stage so one cannot tell much.

1. Besides Unimodular, what other GR proposed replacements have global time...?

Well a world-famous GR expert named Ted Jacobson has something called Einstein-Aether which has a timelike unit-vector field. And Petr Horava at UC Berkeley (pronounced Ho-zha-va) has proposed GR replacement that I believe somebody has gotten a preferred foliation out of. I don't keep track of all the proposed GR replacements. You know about CDT, i guess. Ambjorn and Loll's Causal Dynamical Triangulation. That is built on a preferred foliation. That is slicing spacetime into space like slices so you get layers---essentially a preferred time.
And of course there is Tomita Time that some Loop people have been working on.
And as I told you you get a preferred time in Cosmology as soon as you fill the early universe with hot gas and look at the CMB. Or even if you just have ordinary Friedman model expansion.

2. What do you think about Shape Dynamics?

I told you I think there was a lot of excitement about it which I think peaked a year or two ago. And it is one of SEVERAL proposed replacements that have global time. I wouldn't get excited. Another world-famous GR expert George Ellis just posted on arxiv about Unimodular. I think Unimodular has considerably more legs than SD so if I was going to be interested in one of these i think it might be Tomita Time or Unimodular. Ellis co-authored the classic book on spacetime geometry ("the largescale structure of space time") I have very high regard for his intuition and sense of what matters and where things are going. Unimodular is cool but you couldn't necessarily explain why it is cool to a lay audience in a short popular article or in a book like "Time Reborn". Smolin made an excellent choice in what to use as an example.

I think it is time to LEARN WHAT WE CAN from SD and move on. So I will definitely listen to the Seminar talk by Koslowski when he talks to the Loop people (and not for the first time!) on ILQGS. I'm not an expert or a researcher, but I watch the research scene with interest, and I'm always prepared to be surprised. So we'll see.

Unimodular solves the main Cosmological Constant problem which is a huge plus. If SD would turn out to solve the CC problem that would be significant. Maybe Koslowski will report something on that score. I'm prepared to learn something new from his talk--smart young guy. Maybe you should listen.

 

[amos carine]

I look forward to even such an anouncement about release, and hope that, as far as different models goes, "there will be others proposed." And also, I will try to maintain a capable mental position to keep up with it so as to "stay tuned!..."

My guess is that we might see some advance notices about the Smolin Unger book sometime in next six months.

In the mean time, do you know of any other instances of his scheme or view, or perhaps sources of his?

 

[Ken G]

As is normal for science, we will need to use observations to decide which theory is best. Does Smolin give attention, rather than to philosophical principles which may or may not be true, to what observable features the consequences of those principles might present? It seems to me the highest goal of any theory should be to help us see something in the observations that we would not have otherwise known to look for. What are we looking for in the CMB that we wouldn't have been without these theories? I'm not suggesting there is no answer to that, I am simply curious if there is an answer, and what it is. Much ballyhoo is made about the Gaussian or non-Gaussian nature of the noise, are these philosophical principles, and the theories they motivate, helping us see this data with better eyes, and how?

 

[marcus]

... Does Smolin give attention, ..., to what observable ... consequences...those principles might present?

Yes. He has given a lot of attention to testability and falsifiability. In his writings over the years that have to do with "evolving physical laws" theory, he's made predictions as far back as 1992.

... What are we looking for in the CMB that we wouldn't have been without these theories? ...

The predictions don't involve CMB as far as I know (unless indirectly). They concern measured values of fundamental physical constants, observed masses of neutron stars.

Over the past 5 years or so the basic principles Smolin has mainly been involved with can, I think, be called "temporal naturalism" and "rule-evolution". A recent evolving law MODEL that he has been collaborating on is called "energetic causal sets"---it is in very early stages, preliminary computer simulation simplified models.

It explores how regularities in physical behavior (such as those we call "Laws of Physics") can evolve over time in a simple causal set-up.

If anyone is curious and wants to get a taste of the latest ideas in this area, there's an essay.
Actually all you need to do is google "temporal naturalism" and it is the top hit.
Or you can use this link:
http://arxiv.org/abs/1310.8539
BTW some predictions are discussed on pages 30 and 31, although the essay is primarily philosophical background and overview---and the current theoretical model development (with Cortes) is still in early stages.

 

[marcus]

...My guess is that we might see some advance notices about the Smolin Unger book sometime in next six months.
...

From what I hear actual publication date is expected to be in "Fall 2014". So there might be some advance notices by May 2014, which is six months away. And the schedule might slip of course.
In the meanwhile, as regards Smolin's recent ideas on rule-evolution there's probably all one needs to know already online:
http://arxiv.org/abs/1205.3707
Precedence and freedom in quantum physics
Lee Smolin

http://arxiv.org/abs/1307.6167
The Universe as a Process of Unique Events
Marina Cortês, Lee Smolin

http://arxiv.org/abs/1308.2206
Energetic Causal Sets
Marina Cortês, Lee Smolin

http://arxiv.org/abs/1310.8539
Temporal naturalism
Lee Smolin

For sources on the earlier idea of "Cosmological Natural Selection" (which goes back to 1992) google that or else "cosmic natural selection". CNS is associated with several observational/experiemental predictions, and could in principle, be falsified.

 

[Adrian07]

Here is his page about the Smolin Unger book, it is in draft and the (provisional?) title is:
The Singular Universe--and the Reality of Time.
http://leesmolin.com/writings/the-singular-universe-and-the-reality-of-time/

The book will have two sections, one by each author. The first, more philosophical, and longer portion will be by Unger. The second portion, by Smolin, will have more science-oriented specifics and more physics and cosmology detail.

Here's an excerpt from Lee Smolin's webpage about the draft book.

==quote==
The book develops four inter-related themes:

1) There is only one universe at a time. Our universe is not one of many worlds. It has no copy or complete model, even in mathematics. The current interest in multiverse cosmologies is based on fallacious reasoning.

2) Time is real, and indeed the only aspect of our description of nature which is not emergent or approximate. The inclusive reality of time has revolutionary implications for many of our conventional beliefs.

3) Everything evolves in this real time including laws of nature. There is only a relative distinction between laws and the states of affairs that they govern..

4) Mathematics deals with the one real world. We need not imagine it to be a shortcut to timeless truth about an immaterial reality (Platonism) in order to make sense of its “unreasonable effectiveness” in science.

We argue by systematic philosophical and scientific reasoning , as well as by detailed examples, that these principles are the only way theoretical cosmology can break out of its current crisis in a manner that is scientific, i.e. results in falsifiable predictions for doable experiments.
The book is in two parts: the first part by Roberto Mangabeira Unger and the second, shorter part by Lee Smolin...
==endquote==

I suppose some may believe it. Time I used to think was real but I now realize its just a measure of our universe decaying from its start to its end which makes it more of an illusion. There is far more out there than what we see.
Maths cannot describe an immaterial reality but it does not prove that such a thing does not exist outside our reality.

 

[Chalnoth]

Maths cannot describe an immaterial reality but it does not prove that such a thing does not exist outside our reality.

If math can't describe it, then by definition it can't exist, as long as we include every self-consistent logical structure in math.

 

[cristo]

Let's keep this thread on topic, please.

 

[marcus]

Let's keep this thread on topic, please.

Thanks Cristo! It's an interesting topic (if rather unusual). Smolin (with help of Cortes, Unger…) is attacking the idea that the world can be described as running on unexplained eternal Laws starting from unexplained Initial Conditions.

The topic of the thread is to watch the progress of that attack. Personally I would reserve judgment about it's eventual success: one can watch in an alert but noncommittal way. It might turn out to be significant

As I said there's probably all one needs to know for now already online:

http://arxiv.org/abs/1205.3707
Precedence and freedom in quantum physics
Lee Smolin

http://arxiv.org/abs/1307.6167
The Universe as a Process of Unique Events
Marina Cortês, Lee Smolin

http://arxiv.org/abs/1308.2206
Energetic Causal Sets
Marina Cortês, Lee Smolin

http://arxiv.org/abs/1310.8539
Temporal naturalism
Lee Smolin

The basic goal is to find a single simple causal process which can explain how specific patterns of regularity (aka "laws") can gradually take shape starting from some kind of patternlessness. This single law of causality should explain how it has come about that we have THESE laws of physics, that we observe, and THESE fundamental particles and physical constants, rather than some other operative equations and fields and dimensionless numbers.
Moreover this process of pattern formation (or "law evolution") should be something you can simulate in a computer to some extent, and it should be something you can TEST to see if it is actually still going on at some level. Is Nature still evolving her ways of behavior?

The basic rationale of this program is that things ought to be explained. The Newton paradigm of timeless Eternal Laws with some unexplained Initial Conditions is unsatisfactory in this regard when applied to the whole universe.

The program can, I think, have interesting byproducts:

http://arxiv.org/abs/1311.0186
Twistor relative locality
Lee Smolin
(Submitted on 1 Nov 2013)
We present a version of relative locality based on the geometry of twistor space. This can also be thought of as a new kind of deformation of twistor theory based on the construction of a bundle of twistor spaces over momentum space. Locality in space-time is emergent and is deformed in a precise way when a connection on that bundle is non-flat. This gives a precise and controlled meaning to Penrose's hypothesis that quantum gravity effects will deform twistor space in such a way as to maintain causality and relativistic invariance while weakening the notion that interactions take place at points in spacetime.
10 pages

 

[Ken G]

It sounds like a very interesting project, though I can't be too convinced by the driving motivation that things should be explainable. It seems to me such a goal is internally inconsistent, for if it succeeds, it would look like "I can explain the universe by stipulating that the universe should be explainable," to which I would ask, "please explain why the universe should be explainable." He could only say, "I don't explain that, I accept that and use it to explain the universe," to which I add, "if there is something about the universe you cannot explain, then you have not explained the universe."

 

[yuiop]

I am interested in the global time aspect. Does Lee Smolin anywhere address how he gets around the issue that in Special Relativity there is no global sense of simultaneity? I am guessing that it must be something related to Lorentz Ether Theory which is mathematically identical to Special Relativity, but assumes a background where there is a notion of absolute simultaneity. Due to time dilation and length contraction effects caused by motion relative to the background, the absolute reference frame becomes undetectable by normal methods (but is there by logical deduction).

 

[WannabeNewton]

I am interested in the global time aspect. Does Lee Smolin anywhere address how he gets around the issue that in Special Relativity there is no global sense of simultaneity?

There certainly is a sense of global simultaneity, there is just no unique sense of it. If we have a family of observers whose worldlines are non-intersecting and fill all of space-time, and on top of that the worldlines don't twist around one another, then this family of observers determines a foliation of space-time into space-like hypersurfaces, which are in fact nothing more than the global simultaneity slices for this family. Of course different families determine different foliations hence different global simultaneity slices but clearly the notion itself exists. If the worldlines of the observers in a given family do twist around one another then there is no notion of global simultaneity for this family.

More precisely, given a unit time-like vector field $\xi$ in some space-time $(M,g)$, if $\xi^{\flat}\wedge d\xi^{\flat} = 0$ then $\xi$ determines a space-like foliation of $(M,g)$.

 

[yuiop]

There certainly is a sense of global simultaneity, there is just no unique sense of it.

Yes your right, of course. I should of said something like SR does not admit a preferred reference frame which allows a notion of absolute simultaneity, which appears to be what Lee Smolin is striving for.

 

[Ken G]

But you're right that a lesson of relativity is pretty clearly that the one-to-one matching of simultaneity is only locally a physical concept. Globally there doesn't seem to be any more physical importance to "a bunch of events at different places and the same time" than there is to "a bunch of events at the same place but different times." All that seems to be physically important is the causality relations, which recognize wedges of spacetime rather than hypersurfaces. In that sense, simultaneity is more like a topological relationship than an algebraic one, so I share your question about how Smolin would resurrect a sense of "the march of time." It seems more natural to imagine that time is an emergent property of how our brains make sense of patterns of stimulus.

 

[WannabeNewton]

But you're right that a lesson of relativity is pretty clearly that the one-to-one matching of simultaneity is only locally a physical concept. Globally there doesn't seem to be any more physical importance to "a bunch of events at different places and the same time" than there is to "a bunch of events at the same place but different times." All that seems to be physically important is the causality relations, which recognize wedges of spacetime rather than hypersurfaces. In that sense, simultaneity is more like a topological relationship than an algebraic one, so I share your question about how Smolin would resurrect a sense of "the march of time." It seems more natural to imagine that time is an emergent property of how our brains make sense of patterns of stimulus.

All you have done here is put together random, completely unrelated terms into an incomprehensible paragraph.

 

[Ken G]

So you didn't get the message that relativity apportions all events into three sets, with regard to the here and now, which are the sets of "future", "past", and "possible present", in regard to what the here and now can cause, can be caused by, or can have no such relation with, respectively? Cuz I thought that's what I said pretty clearly. The point is, mathematical expressions are concise and precise, but meaning matters too.

As for time being emergent from our processing of data, I should think that would be the pretty obvious alternative to Smolin's perspective on it as a fundamentally real entity. To understand one person's view, it is often useful to juxtapose it with an opposite perspective. Again, meaning.

 

[WannabeNewton]

You're blabbering again. If you want to be clear then just explicitly use math, there is no need for wordplay. How does any of what you said have any relation to local/global simultaneity being a "topological relationship"?

 

[Ken G]

I wonder if you always conclude that everything you personally don't understand is blabber. It's certainly an easy position to take, but not conducive to much learning. For example, it seems that you feel that only syntactic expressions have any value, but from my perspective that's just silly. Perhaps you should think more on the differences between syntax and semantics.

 

[marcus]

Let's keep this thread on topic, please.

Thanks Cristo! It's an interesting topic (if rather unusual). Smolin (with help of Cortes, Unger…) is attacking the idea that the world can be described as running on unexplained eternal Laws starting from unexplained Initial Conditions.

The topic of the thread is to watch the progress of that attack. Personally I would reserve judgment about it's eventual success: one can watch in an alert but noncommittal way. It might turn out to be significant

As I said there's probably all one needs to know for now already online:

http://arxiv.org/abs/1205.3707
Precedence and freedom in quantum physics
Lee Smolin

http://arxiv.org/abs/1307.6167
The Universe as a Process of Unique Events
Marina Cortês, Lee Smolin

http://arxiv.org/abs/1308.2206
Energetic Causal Sets
Marina Cortês, Lee Smolin

http://arxiv.org/abs/1310.8539
Temporal naturalism
Lee Smolin

The basic goal is to find a single simple causal process which can explain how specific patterns of regularity (aka "laws") can gradually take shape starting from some kind of patternlessness. This single law of causality should explain how it has come about that we have THESE laws of physics, that we observe, and THESE fundamental particles and physical constants, rather than some other operative equations and fields and dimensionless numbers.
Moreover this process of pattern formation (or "law evolution") should be something you can simulate in a computer to some extent, and it should be something you can TEST to see if it is actually still going on at some level. Is Nature still evolving her ways of behavior?

The basic rationale of this program is that things ought to be explained. The Newton paradigm of timeless Eternal Laws with some unexplained Initial Conditions is unsatisfactory in this regard when applied to the whole universe.
...

How about we follow Cristo's suggestion (he moderates Cosmo forum) and keep on the topic of Smolin and Cortes' specific ideas? Members could check out their actual papers and make sure to focus on discussing them. Have I given a fair paraphrase or summary of the main direction of their research as shown in the above 4 papers? Did I miss some significant feature that you can point out?

 

[marcus]

By the way, in the Temporal Naturalism paper that just appeared Smolin appeals to the following four principles which he finds helpful in the search for a correct cosmological theory.
• Principle of (aspiration for) sufficient reason.
• Principle of the identity of the indiscernible.
• Principle of causal closure: the universe contains all its causes.
• Principle of reciprocity: if an element of nature, A, can influence change in an element B, the reverse must also be the case.

These principles were formulated by Leibniz.

It's to some extent based on these principles that Smolin mounts his attack on the idea of the universe run according to fixed eternal laws (the Newtonian picture), and proposes that the regular patterns we see (and call physical laws) must be changing.

As Feynman pointed out, this would offer an historical or evolutionary explanation why the laws of physics are what they are and not something different---they evolved---and thus accord with the principle of sufficient reason (that there should be an explanation for things being this way rather than otherwise).

It would also accord with the principle of reciprocity. We wouldn't be postulating an eternal law that is outside of time and acts on things (e.g. electrons) without itself, in turn, being acted upon in the reciprocal action-reaction manner widely observed in nature.

Here's an excerpt from the abstract of the Temporal Naturalism paper:

==quote Smolin http://arxiv.org/abs/1310.8539 ==
... One version, which I call temporal naturalism, holds that time, in the sense of the succession of present moments, is real, and that laws of nature evolve in that time. This is contrasted with timeless naturalism, which holds that laws are immutable and the present moment and its passage are illusions. I argue that temporal naturalism is empirically more adequate than the alternatives, because it offers testable explanations for puzzles its rivals cannot address, and is likely a better basis for solving major puzzles that presently face cosmology and physics...
==endquote==

 

[petm1]

Thank you marcus, you always have the best links.

 

[Ken G]

How about we follow Cristo's suggestion (he moderates Cosmo forum) and keep on the topic of Smolin and Cortes' specific ideas? Members could check out their actual papers and make sure to focus on discussing them. Have I given a fair paraphrase or summary of the main direction of their research as shown in the above 4 papers? Did I miss some significant feature that you can point out?

I was hoping you could comment on whether Smolin addresses the paradox of using as a fundamental tenet that the universe should be explainable, while recognizing that choosing any starting point always means taking something as itself unexplainable. Also, another issue of interest is how Smolin justifies regarding time as real rather than as a conceptual tool used by our minds to organize and experience stimulus. The latter point he may not need to address, it is merely an alternative picture of what time is, but the former seems like a challenge to his fundamental premise. Indeed, it seems to me that one can have temporal naturalism without asserting that time be real, one can simply access greater organizational power by letting the concept extend to the evolution of laws. In other words, there is a difference between seeking a means of being able to explain more things, and a requirement that we adopt a perspective that all must be explainable. The latter premise seems like a logical contradiction.

 

[WannabeNewton]

I wonder if you always conclude that everything you personally don't understand is blabber.

I can't understand statements that make no sense mathematically. If you don't know the math then don't throw in a mix of random terms to form a string of nonsense that you think sounds technical enough to pass as understandable. I asked you to prove in what sense local/global simultaneity are, according to you, "topological relationships" as opposed to "algebraic relationships" and you haven't so don't blame me for it.

 

[Ken G]

So you've picked out two phrases from ten sentences and from that you conclude that none of it makes any sense? Fascinating. But I should have clarified when you asked before. By an "algebraic" relation, I mean only that in the old way of thinking, we could seek a formula that would tell us, by mapping our spacetime coordinates into theirs, what our "now" means for some distant observer. But by the new way of thinking, any such formula is a relatively arbitrary coordinate convention, which cannot have physical content unless it crosses the topological borders of the light cone. By "topological", I simply mean that the light cone divides events into three open sets that can be mapped into themselves by arbitrary coordinatizations, maintaining only their distinctions as three separate causality sets. That's a very different way of thinking about "future", "past", and "present", which cares more about the set that the events belong to than it does to where in that set the event lies.

It's true that the proper time does have a quantifiable value along a path between events, but the reliance on path makes it a higher order functional than the algebraic relations we used to think that spacetime events could be classified using. Special algebraic relations on the spacetime coordinates also exist, such as those that find the proper time along inertial paths, but in relativity, an inertial path holds no particular added significance, in that the postulates hold even for observers on noninertial paths. So the bottom line is, spacetime is a much different place in relativity, because there is no universal meaning of simultaneity, and the quantifications of separation depend on the path between the events, not just the difference in time coordinate like for Newton. Put all that together, and the idea that "time is real" is significantly challenged, requiring a much more sophisticated way to think about what Smolin might mean by "real time." Hence the relevance to this thread.

 

[kye]

Well a world-famous GR expert named Ted Jacobson has something called Einstein-Aether which has a timelike unit-vector field. And Petr Horava at UC Berkeley (pronounced Ho-zha-va) has proposed GR replacement that I believe somebody has gotten a preferred foliation out of. I don't keep track of all the proposed GR replacements. You know about CDT, i guess. Ambjorn and Loll's Causal Dynamical Triangulation. That is built on a preferred foliation. That is slicing spacetime into space like slices so you get layers---essentially a preferred time.
And of course there is Tomita Time that some Loop people have been working on.
And as I told you you get a preferred time in Cosmology as soon as you fill the early universe with hot gas and look at the CMB. Or even if you just have ordinary Friedman model expansion.

How many percentage of physicists think of this preferred time? Lee Smolin based it on the Big Bang and CMB. For weeks I still can't decide what to make of this. Do you guys treat a global preferred time as a global preferred frame? is it the same? For those who knows arguments where the big bang and CMB are Lorentz invariant and there can't be preferred time, please share it now... the following is the logic behind Lee Smolin belief in it (anyone has counterarguments?) from his book "Time Reborn" (shared for sake of discussion).

"Before discussing how theory might resolve this contradiction, let’s look at what experiment
has to say. A preferred global notion of time implies a preferred observer, whose clock
measures that preferred time. This contradicts the relativity of inertial frames, according to
which there is no experimental or observational way to distinguish an observer supposedly
at rest from those moving with a constant but arbitrary velocity.
The first thing to note is that the universe is arranged in a way that does indeed pick out
a preferred state of rest. We know this because when we look around with our telescopes
we see the great majority of galaxies moving away from us at roughly the same speed in
every direction. But this can only be true of one observer, because someone moving rapidly
away from us and into space would see those galaxies ahead of her, which she is catching
up with, moving slower than those behind her. Moreover, we have good evidence that the
galaxies are uniformly distributed in space, at least when their positions are averaged over
a sufficiently large scale—that is, the universe seems to be the same when looked at in any
direction. From these facts, we can deduce that at each point in space there will be one
special observer who sees the galaxies moving away from her at the same speed in every
direction.3 So the motions of the galaxies pick out a preferred observer, and hence a preferred
state of rest, at each point in space.
Another way to fix a preferred family of observers is to use the cosmic microwave background.
These preferred observers see the CMB coming at them at the same temperature
from all directions in the sky.4
Happily, the two families of preferred observers coincide. The galaxies appear, on average,
to be at rest in the same reference system in which the CMB comes at us at the same
temperature from all directions. So the universe is organized in a way that picks out a preferred
state of rest. But this fact need not contradict the principle of the relativity of motion.
A theory can have a symmetry that is not respected by its solutions. To the contrary:
Solutions of theories often break the theories’ symmetries. The fact that there is fundamentally
no preferred direction in space does not prevent the wind from blowing from the north
today. Our universe represents just one solution to the equations of general relativity. That
one solution can be asymmetric—that is, it can include a preferred state of rest—without
contradicting the principle that the theory has a symmetry. The universe might have started
off in a way that broke the symmetry."

 

[marcus]

"... So the universe is organized in a way that picks out a preferred
state of rest. But this fact need not contradict the principle of the relativity of motion.
A theory can have a symmetry that is not respected by its solutions. To the contrary:
Solutions of theories often break the theories’ symmetries. ..."

There is no contradiction. Smolin says obvious things, in your quote. What is your problem? Essentially ALL cosmologists use a preferred idea of time and a preferred state of rest, for the reasons he says.
The CMB ancient light gives the most precise criterion of rest, but he gives a more general argument. The CMB only confirms more precisely what was already known since 1940 or earlier, from Hubble and others.

The other preferred time which I mentioned by name was "Tomita time" or "thermal time". It was identified and discussed by Alain Connes and Carlo Rovelli in the 1990s. It is a theoretical concept based on the *quantum* state of the universe.

I don't think it is advisable to decide issues based on "what percentage of physicists" think this or that. You would have to make an opinion poll to find out. What matters is what the EXPERTS in a certain AREA of physics think. We know that because the experts are the ones who write the research publications in that area and who are invited to speak at the major international conferences. Science is not a "one-man-one-vote" democracy.

Probably only a small percentage of physicists know about "Tomita time" (they would be the experts in quantum gravity and General Relativity) but nevertheless it is still very interesting. Also Rovelli has shown that within a certain quantum cosmology framework the Tomita time of Connes and Rovelli AGREES with the preferred time normally used by cosmologists.

 

[kye]

There is no contradiction. Smolin says obvious things, in your quote. What is your problem? Essentially ALL cosmologists use a preferred idea of time and a preferred state of rest, for the reasons he says.
The CMB ancient light gives the most precise criterion of rest, but he gives a more general argument. The CMB only confirms more precisely what was already known since 1940 or earlier, from Hubble and others.

The other preferred time which I mentioned by name was "Tomita time" or "thermal time". It was identified and discussed by Alain Connes and Carlo Rovelli in the 1990s. It is a theoretical concept based on the *quantum* state of the universe.

I don't think it is advisable to decide issues based on "what percentage of physicists" think this or that. You would have to make an opinion poll to find out. What matters is what the EXPERTS in a certain AREA of physics think. We know that because the experts are the ones who write the research publications in that area and who are invited to speak at the major international conferences. Science is not a "one-man-one-vote" democracy.

Probably only a small percentage of physicists know about "Tomita time" (they would be the experts in quantum gravity and General Relativity) but nevertheless it is still very interesting. Also Rovelli has shown that within a certain quantum cosmology framework the Tomita time of Connes and Rovelli AGREES with the preferred time normally used by cosmologists.

So all cosmologists who use the idea of Preferred time is comfortable or accept that the quantum correlations can be synchronized via a preferred global time (as Smolin mentioned).. and hence a preferred global frame? Because if you will review the literature on quantum entanglement.. nowhere or rarely is this notion of global preferred time used to explain why there are correlations... or is it due to the fact that quantum entanglement occur in local sector of the universe hence can't use the global preferred time? What do quantum physicists who study quantum correlations think about global preferred time?

 

[marcus]

So all cosmologists who use the idea of Preferred time is comfortable or accept that the quantum correlations can be synchronized ?

Nope. Why should they? Cosmologists just use a preferred rest frame (and universe-time) going back to I guess 1940 or earlier (with Hubble and others).
That is all classical, and specific to their specialty. Smolin explained this in very clear language in what you quoted.

 

[kye]

Nope. Why should they? Cosmologists just use a preferred rest frame (and universe-time) going back to I guess 1940 or earlier (with Hubble and others).
That is all classical, and specific to their specialty. Smolin explained this in very clear language in what you quoted.

when bells theorem was found to be violated. why didnt physicists jump on the cosmologist preferred rest frame of the universe and CMB idea to explain the correlerations? isn't it not related with the relativity of simultaneity in special relativity or having conflict? or in other words, what can you say about the relativity of simultaneity and the cosmologists idea of global rest frame. is it not in contradiction or connected? or to put it another way, you have to replace special relativity to make the quantum entanglement use a preferred frame that is not related to the cosmologists rest frame?

 

[Chalnoth]

I'm not so sure I like the language "preferred". I think "convenient" is a more apt term. It's a rest frame that makes our universe appear more symmetric, which is convenient because it makes our calculations simpler. It has nothing whatsoever to do with the classical notion of a "preferred frame" which certainly doesn't exist. Nor does it have any implications for simultaneity or Bell's theorem.

Incidentally, though, special relativity and quantum mechanics play together quite nicely. It's General Relativity that has issues.

 

[kye]

I'm not so sure I like the language "preferred". I think "convenient" is a more apt term. It's a rest frame that makes our universe appear more symmetric, which is convenient because it makes our calculations simpler. It has nothing whatsoever to do with the classical notion of a "preferred frame" which certainly doesn't exist. Nor does it have any implications for simultaneity or Bell's theorem.

Incidentally, though, special relativity and quantum mechanics play together quite nicely. It's General Relativity that has issues.

Or to give a more accurate question (to Markus in case you are not familiar with him). Is Smolin conjecturing that Special Relativity has one foliation of spacetime which uses the Universe or CMB global preferred frame? Or is Smolin idea of universe preferred frame and SR different.. meaning to say.. he has to modify SR to make one of its framed preferred (synchronized to the universe global rest or CMB frame)?? I'm somewhat confused when I read this aspect of Lee Smolin book Time Reborn.

 

[Chalnoth]

Is Smolin conjecturing that Special Relativity has one foliation of spacetime which uses the Universe or CMB global preferred frame?

Special relativity has no preferred frame at all. So this statement really doesn't make sense.

Or is Smolin idea of universe preferred frame and SR different.. meaning to say.. he has to modify SR to make one of its framed preferred (synchronized to the universe global rest or CMB frame)?? I'm somewhat confused when I read this aspect of Lee Smolin book Time Reborn.

This is a somewhat different idea. It's a proposed way of modifying special relativity. Such things have been proposed over the years, but none has really made any traction.

 

[marcus]

Kye you quoted a nice clear passage from Smolin's book NOT having to do with his recent theorizing especially but more with conventional cosmology going back to first half of 20th century.

...
The first thing to note is that the universe is arranged in a way that does indeed pick out
a preferred state of rest. We know this because when we look around with our telescopes
we see the great majority of galaxies moving away from us at roughly the same speed in
every direction. But this can only be true of one observer, because someone moving rapidly
away from us and into space would see those galaxies ahead of her, which she is catching
up with, moving slower than those behind her...
Another way to fix a preferred family of observers is to use the cosmic microwave background.
These preferred observers see the CMB coming at them at the same temperature from all directions in the sky...

Indeed empty Minkowski space, with no matter or radiation in it, lacks any conventional preferred time axis or state of rest. But empty space is not realistic, and as soon as you put in some matter and or radiation (especially if it is evenly distributed) you establish them. Here is how Smolin continues, in the passage you quoted:

==Smolin's book continued==

So the universe is organized in a way that picks out a preferred state of rest. But this fact need not contradict the principle of the relativity of motion. A theory can have a symmetry that is not respected by its solutions.
Our universe represents just one solution to the equations of general relativity. That
one solution can be asymmetric—that is, it can include a preferred state of rest—without
contradicting the principle that the theory has a symmetry. The universe might have started
off in a way that broke the symmetry.

==endquote==

You could say that physics is all about the ways that symmetry is broken. And we still have a lot to learn about the ways that happens.

You might find the "QBism" paper by Fuchs Mermin Schack interesting. It is very readable: clear non-technical verbal reasoning for the most part. Essentially it is telling us about yet another way in which symmetry is broken, built into the very bones of quantum mechanics itself (by the importance it gives to the observer). I won't explain, you'd enjoy finding out for yourself what they are saying and what "QBism" (pronounced like the modern art style Cubism) is about.

 

[kye]

Kye you quoted a nice clear passage from Smolin's book NOT having to do with his recent theorizing especially but more with conventional cosmology going back to first half of 20th century.

Indeed empty Minkowski space, with no matter or radiation in it, lacks any conventional preferred time axis or state of rest. But empty space is not realistic, and as soon as you put in some matter and or radiation (especially if it is evenly distributed) you establish them. Here is how Smolin continues, in the passage you quoted:

But Marcus, Smolin tried to seek a global preferred frame to explain Bell's Theorem. His statement is clear as shared previously and again quoted:

"To describe how the correlations are established, a hidden-variables theory must embrace
one observer’s definition of simultaneity. This means, in turn, that there is a preferred notion
of rest. And that, in turn, implies that motion is absolute. Motion is absolutely meaningful,
because you can talk absolutely about who is moving with respect to that one observer—
call him Aristotle. Aristotle is at rest. Anything he sees as moving is really moving.
End of story.
In other words, Einstein was wrong. Newton was wrong. Galileo was wrong. There is no
relativity of motion"

Markus. This can only happen by altering SR and making the universe global frame the preferred frame. Or maybe you mean the following:

Matter and forces obey SR and has no preferred frame
Wave function can distinguish the universe global preferred frame and use it

Isn't this what Smolin had in mind? If not, how would his non-local hidden variable which he is seeking work?

 

[Chalnoth]

But Marcus, Smolin tried to seek a global preferred frame to explain Bell's Theorem. His statement is clear as shared previously and again quoted:

"To describe how the correlations are established, a hidden-variables theory must embrace
one observer’s definition of simultaneity. This means, in turn, that there is a preferred notion
of rest. And that, in turn, implies that motion is absolute. Motion is absolutely meaningful,
because you can talk absolutely about who is moving with respect to that one observer—
call him Aristotle. Aristotle is at rest. Anything he sees as moving is really moving.
End of story.
In other words, Einstein was wrong. Newton was wrong. Galileo was wrong. There is no
relativity of motion"

The broader context helps here. I found this passage in a quick Google search:
http://books.google.com/books?id=zH84LQ7-wAQC&pg=PA163&lpg=PA163#v=onepage&q&f=false

This is a hypothetical statement he's making.

 

[DennisN]

Just found a brand new video, "Lee Smolin (Perimeter Institute) on Time Reborn" (Published on Dec 12, 2014):



...which I am going to watch now :). Merry Christmas, by the way!

 

[marcus]

DennisN, thanks for the link! Chalnoth, good point. I have the book, in that passage that Kye quoted, Smolin was NOT presenting his own viewpoint. Kye took something unrepresentative out of context. That was on page 163, where he was showing the contradiction between two views and posing a dilemma. If you want to get a better idea of what he's saying you need to turn the page to where the next chapter starts---that's where he starts to RESOLVE the tension and present a THIRD position.

 

[marcus]

...
Isn't this what Smolin had in mind? If not, how would his non-local hidden variable which he is seeking work?

Apparently not what he has in mind. The passage you quoted is setting out a contradictory position that he does not subscribe to. To understand what he is seeking and how it is intended to work you have to turn the page and start the next chapter.

I think the way Smolin is seeking to resolve the contradictions he presents there is changing in a subtle way. In the book you quoted (if you read on further) you see he relies on the example of an alternative to General Relativity called Shape Dynamics where you get a kind of local equivalence to GR and locally no preferred rest, or preferred time, but there is a preferred time for the universe as a whole which we cannot determine or track with physical clocks.

However that book appeared over a year ago (April 2013) and probably was mostly written some two or three years ago. If I look at the current work of Smolin and co-author Marina Cortes, I see them interested in a different alternative to GR called Energetic Causal Sets.

This ECS gives what I suspect is a more sophisticated instance of the kind of thing Smolin is looking for. I think his approach has to some extent evolved. But that is just my take, can't speak with any assurance. Here's a sample of recent Cortes Smolin work:
http://arxiv.org/abs/1407.0032