Developments in Shape Dynamics

I'm not knowledgeable enough to discuss this, but I see that this paper has been cited at least 43 times, some fairly recent, so there seems to be some interest-

http://arxiv.org/cits/1105.0183

This paper looks to be a good reference/undergrad introduction-

http://arxiv.org/abs/1409.0105

 

I saw a talk by Barbour on this topic a few years back. It was rather interesting.

His central conceit is that the concept of time we use in physics is incorrect. He points out that there's no such thing as an ideal clock: the actual behavior of any clock actually depends upon the structure of the entire universe (naturally, things further away have less and less impact on the clock, but it is technically true that the structure of the entire universe has some impact). He uses this idea to claim that time should not be considered a parameter in the theory, or even a fourth dimension, but instead as an emergent property. He produces a theory which seems to replicate the results of General Relativity with no time parameter and using only three dimensions (with time being calculable from the configuration of the space).

I didn't really understand his theory, and it didn't seem to me that his criticisms of the standard paradigm were well-founded, but I thought it was an interesting idea.

 

Maybe this is the talk?

http://www.perimeterinstitute.ca/videos/shape-dynamics-and-general-relativity

His web site is-

http://www.platonia.com/index.html

 

Looks like the same talk, yes. Different venue, but same basic talk.

 

Some may find these papers of interest: http://arxiv.org/abs/1409.0105, A Shape Dyamics Tutorial; and http://arxiv.org/abs/1411.4316, Where to Apply Relationalism.

 

There has been a great deal of progress in Shape Dynamics in the last few years. Much of it due to Koslowski, Gryb and Gomes who have extended Barbour's best matching principle from a Lagrangian formulation to a canonical one. This has allowed them to develop the method of gauge symmetry trading, with which they have constructed Shape Dynamics as a theory which is dual to General Relativity in a particular gauge fixing.

By "dual" I mean the two theories are locally equivalent, everywhere giving the same equations of motion. This is similar to the ADS/CFT correspondence except at a fully classical level.

This trading of symmetries allows them to resolve two facets of the long standing "Problem of Time" which has plagued Quantum Gravity research, "many fingered time" and the "frozen formalism".

Some recent papers:-

"The shape dynamics description of gravity"
Tim Koslowski
http://arxiv.org/abs/1501.03007

"The Solution to the Problem of Time in Shape Dynamics"
Julian Barbour, Tim Koslowski, Flavio Mercati
http://arxiv.org/abs/1302.6264

"Identification of a gravitational arrow of time."
Julian Barbour, Tim Koslowski, Flavio Mercati
http://arxiv.org/abs/1409.0917

"A Shape Dynamical Approach to Holographic Renormalization"
Henrique Gomes, Sean Gryb, Tim Koslowski, Flavio Mercati, Lee Smolin
http://arxiv.org/abs/1305.6315

There was an interesting exchange between Lee Smolin and Julian Barbour at the end of Barbour's presentation at the Perimeter Institute where Smolin asks something like "rather than eliminate time haven't you found a universal time?" Barbour agreed that was a reasonable interpretation.

 

Also from the same line :

http://arxiv.org/abs/1302.7037
Loop Quantization of Shape Dynamics
Tim Koslowski

http://arxiv.org/abs/1303.0060
Differences and similarities between Shape Dynamics and General Relativity
Henrique Gomes, Tim Koslowski

 

Haven't read this but this sounds intuitively more natural to me, from a far more basic perspective : any internal frequency is sufficient for an observer to experience time, while complex interactions with other systems are required to even define space.

 

I have been trying to find the time to reread Time Reborn before tackling Unger/Smolin, so this is just from memory. The impression I had is that the idea of the primacy of time while consistent with his fecund universe model is not necessarily dependent on it.
I don't see how it can be made consistent however as one of the guiding principles in Time Reborn is a sort of cosmological version of Leibniz' Principle of Sufficient Reason, where all effects have a cause which is within the universe. This seems to be broken if the universe is emerging from somewhere now causally disconnected. It leaves the same explanatory gap as the initial singularity in BBT.

Smolin and Unger appear to disagree about the importance of Leibniz though so hopefully there will be some decent discussion on this point in the latest book.

 

Forgot to mention that the exchange between Smolin and Barbour starts about 75 minutes in at the link given by websterling in post #5.
(Edit to correct post number)