Thread: Latest Paper by T. Padhmanaban may 2014

Here is the link :

http://arxiv.org/pdf/1405.5535v1.pdf

ABSTRACT

"I show that in a general, evolving spacetime, the rate of change of gravitational
momentum is related to the difference between the number of degrees of freedom in
the bulk and the boundary of a region. This expresses the gravitational field equa-
tion in the thermodynamic language (in contrast with the conventional geometric
language) which is the natural description, if gravity is an emergent phenomenon.
In all static spacetimes, the number of degrees of freedom in the boundary is equal
to the number of degrees of freedom in the bulk; i.e., these spacetimes maintain
holographic equipartition. It is the departure from holographic equipartition that
drives the time evolution of the spacetime. This result, which is equivalent to
Einstein’s equations, provides an elegant, holographic, description of spacetime
dynamics."


CONCLUSION

"This strengthens the idea
that gravitational field equations have the same conceptual status as the equations of
thermodynamics or fluid mechanics, with the Davies-Unruh temperature providing the
link between microscopic and macroscopic descriptions of spacetime. It is remarkable
that the dynamical evolution of the spacetime can be described in such an elegant,
holographic language which is closer to thermodynamics than to geometry."




>> I'm interested in your reactions on this paper.

What's it about?

Originally Posted by Daecon

What's it about?

It's about 6 pages.

Originally Posted by Daecon

What's it about?

I added the abstract and the conclusion to give you an idea.

I noticed that out of the 5 references in the paper, one was from 1975, and the other 4 he was referencing himself. All his self-references were to papers on arvix, none of which was peer reviewed.

Originally Posted by AlexG

I noticed that out of the 5 references in the paper, one was from 1975, and the other 4 he was referencing himself. All his self-references were to papers on arvix, none of which was peer reviewed.

No, look more carefully, all of his references are published . In very reputable journals. He simply gives the arxiv link as an addition.

This paper is a continuation on his larger 2009 paper 'Thermodynamical aspects of gravity : new insights', containing 150 references, only a very small portion being his own papers. In turn that 2009 paper was an important reference in Erik Verlindes 2010 paper 'On the origin of gravity and the laws of Newton, and an influence on his work after 2010.

I stand corrected.

Here are a couple of less technical articles by him:
2Physics: Gravity : An Emergent Perspective
http://www.iucaa.ernet.in/~paddy/res...nalarticle.pdf

Just a few comments here. Firstly, Thanu Padhmanaban is one of the foremost experts on gravitational physics alive today. His textbook "Gravitation: Foundation and Frontiers" is well on track to become a standard text alongside MTW and Wald, although it must be said that it is highly technical and definitely not your run-of-the-mill undergrad text. In any case, he is a genuine researcher and brilliant academic, albeit not one who is widely known outside academic circles.

>> I'm interested in your reactions on this paper.

I closely follow both gr-qc and hep-th on arXiv, and Padhmanaban is in my favourites along with a few others, so I read this paper when it was first uploaded. It is very interesting, though many of the details elude me for lack of mathematical knowledge; however, it goes along very nicely with some of the things I had mentioned on your other thread. The basic idea of this paper is that the future-oriented foliation of hypersurfaces ( i.e. the "succession of moments of time" ) arises from a relationship between a hypervolume and its surface, called the holographic equipartition principle. I would lie if I said I understand everything involved in this, but basically what he is pointing out that there is a link between macroscopic gravitation and the microscopic structure of the vacuum given by Unruh radiation, i.e. the fact that accelerated observers see a different vacuum ground state.

Padhmanaban has been working on these ideas for some time, so this paper is an elaboration on previous proposals.

I forgot to mention the following - while there are remarkable parallels between gravity and thermodynamics, Verlinde's original idea of "entropic gravity" appears to be in conflict with experimental data. I wasn't aware of this until KJW pointed it out a while back, but the paper outlining this seems quite convincing :

http://alpha.sinp.msu.ru/~panov/Lib/...009.5414v1.pdf

It seems that this is an ongoing discussion
with arguments and counter arguments

http://arxiv.org/pdf/1104.4650v2.pdf

Originally Posted by Noa Drake

It seems that this is an ongoing discussion
with arguments and counter arguments

http://arxiv.org/pdf/1104.4650v2.pdf

Interesting I'd call it a healthy debate !

Healthy debate ! Excellent.