Thermodynamics of Spacetime: The Einstein Equation of State?

  • Thread starter mtak0114
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  • #1
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Hi,

I have recently been delving into Quantum gravity related material... and I came accross a paper by Ted Jacobson "Thermodynamics of Spacetime: The Einstein Equation of State" http://arxiv.org/abs/gr-qc/9504004 and as far as I understand the argument it is very impressive who would have thought that three seemingly unrelated theories could be so closely tied (GR, thermo and QFT). But I have two questions:

1) Why starting from the 2nd law which assumes an arrow of time can we extract a theory which is time reversal invariant GR? (this is probably closely related to the work of Hawking which I am unfamiliar with)

2) His interpretation of heat puzzles me:

"In thermodynamics, heat is energy that flows between degrees of freedom
that are not macroscopically observable. In spacetime dynamics, we shall
define heat as energy that flows across a causal horizon."
specifically he identifies [tex]Q[/tex] (the heat) with [tex]T^{\alpha\beta}[/tex] (the energy momentum tensor.)

cheers

M
 

Answers and Replies

  • #2
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This seems dependent on the holographic principle/conjecture...and all these things tie together when entropy is considered as information...

entropy is a measure of hidden information (not macroscopically observable) with heat and entropy closely related.

wiki has some insights at: http://en.wikipedia.org/wiki/Laws_of_black_hole_mechanics

I hesitate to make any other comments as I would be as likely to mislead as enlighten.

Leonard Susskind has good discussion on this general subject, THE BLACK HOLE WAR, in various places under thermo/heat/entropy as does Charles Seife, DECODING THE UNIVERSE, including pages 70 to 85...
 

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