Arcadian Functor

occasional meanderings in physics' brave new world

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Marni D. Sheppeard

Friday, October 03, 2008

Machian Gravity

There are a number of interesting talks at Perimeter this week, including one talk by Julian Barbour on Machian gravity. In a strictly classical analysis, Barbour derives GR, and then SR, from a Machian geodesic principle applied to a shape space of particle configurations, in which Time is merely emergent. Carl will just love the long discussion about action principles and square roots, as well as the introductory remark that GR, as usually practiced, is fundamentally flawed for its treatment of Time.

Barbour concluded the talk by offering fqxi funding for research on Machian quantum gravity. Of course I immediately emailed him to apply for the funding.

See also the talks by Abramsky and Penrose. Abramsky managed to introduce Category Theory in a very sneaky fashion, after a 20 minute introduction.


Blogger L. Riofrio said...

Cool. maybe I'll contact Barbour too. Keep applying for postdocs.

October 03, 2008 6:01 PM  
Blogger Kea said...

Yes, you must. He's offering accommodation in his large old farmhouse near Oxford!

October 03, 2008 6:05 PM  
Blogger Matti Pitkanen said...

It seems that there are at least four schools about time: 1 time only, no time at all, 2 times, and even 3 times;-).

Barbour's view makes sense if one beliefs on canonical quantization of GRT. In canonical quantization of GRT Hamiltonians vanish identically and the natural conclusion is that there is no time. Canonical quantization is however based on Newtonian view about time and means that quantum states are essentially time=constant snapshots. This view must be given up already in Special Relativity. To my opinion classical GRT treats geometric time correctly although GRT as such is not completely correct theory.

As a representative of 2-time school I believe that the problems are created by the identification of geometric time with the experienced time and present already in Special Relativity and Newtonian mechanics. I do not believe that these problems can be solved without the extension of physics to a theory of consciousness.

General Coordinate Invariance poses very powerful constraints on this extension. One implication is that the contents of conscious experience must be about 4-D space-time regions rather than about time=constant snapshots. Among other things this means new view about memory. That General Coordinate Invariance allows to predict something highly non-trivial about neuroscience is to me a news! Especially so because the predictions conform with what we know and explain why the attempts to identify the "memory files" of past in brain have failed. It is also known that lab animals, whose brain regions believed to serve as memory storages are destroyed (I would not like to be practicing neuro scientist) can remember.

October 04, 2008 6:47 PM  
Blogger CarlBrannen said...


There were some things I liked but not much. On the other hand, check out this lecture by Jos Uffink, which reads directly on MUBs and thermodynamics.

October 05, 2008 8:57 AM  

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