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General proof of the entropy principle for self-gravitating fluid in static spacetimesPowerPoint Presentation

General proof of the entropy principle for self-gravitating fluid in static spacetimes

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### General proof of the entropy principle for self-gravitating fluid in static spacetimes

高思杰 (Gao Sijie)

北京师范大学

(Beijing Normal University)

2014 Institute of Physics, Academia Sinica

Outline fluid in static spacetimes

- Introduction
- Entropy principle in spherical case --radiation
- Entropy principle in spherical case –perfect fluid
- Entropy principle in static spacetime
- Related works
- Conclusions.

2014 Institute of Physics, Academia Sinica

1. Introduction fluid in static spacetimes

Mathematical analogy beween thermodynamics and black holes:

2014 Institute of Physics, Academia Sinica

2014 Institute of Physics, Academia Sinica fluid in static spacetimes

What is the relationship between fluid in static spacetimesordinary thermodynamics and gravity?

We shall study thermodynamics of self-gravitating fluid in curved spacetime.

2014 Institute of Physics, Academia Sinica

Consider a self-gravitating perfect fluid with spherical symmetry in thermal equilibrium:

S: total entropy of fluid

M: total mass of fluid

N: total particle number

fluid

There are two ways to determine the distribution of the fluid:

1. General relativity: Einstein’s equation gives Tolman-Oppenheimer-Volkoff

(TOV ) equation:

2. Thermodynamics: at thermal equilibrium.

Are they consistent?

2. Entropy principle in spherical case---radiation symmetry in thermal equilibrium:

Sorkin, Wald, Zhang, Gen.Rel.Grav. 13, 1127 (1981)

In 1981, Sorkin, Wald, and Zhang (SWZ) derived the TOV equation of a self-gravitating

radiation from the maximum entropy principle.

Proof: The stress-energy tensor is given by

The radiation satisfies:

2014 Institute of Physics, Academia Sinica

Assume the metric of the spherically symmetric radiation takes the form

The constraint Einstein equation

yields

2014 Institute of Physics, Academia Sinica

Since , the extrema of is equivalent to the Euler-Lagrange equation:

2014 Institute of Physics, Academia Sinica

3. Entropy principle in spherical case---general perfect fluid (Sijie Gao, arXiv:1109.2804,Phys. Rev. D 84, 104023 )

- To generalize SWZ’s treatment to a general fluid, we first need to find an expression for the entropy density .
- The first law of the ordinary thermodynamics:
Rewrite in terms of densities:

Expand:

The first law in a unit volume:

2014 Institute of Physics, Academia Sinica

Thus, we have the Gibbs-Duhem relation fluid

2014 Institute of Physics, Academia Sinica

Note that fluid

Thus,

4.Proof of the entropy principle for perfect fluid in static spacetimesarXiv: 1311.6899

- In this work, we present two theorems relating the total entropy of fluid to Einstein’s equation in any static spacetimes.
- A static spacetime admits a timelike Killing vector field which is hypersurface orthogonal.

2014 Institute of Physics, Academia Sinica

2014 Institute of Physics, Academia Sinica spacetimes

Proof of Theorem 1 spacetimes

2014 Institute of Physics, Academia Sinica

The total entropy spacetimes

Its variation:

Total number of particle:

The constraint

2014 Institute of Physics, Academia Sinica

Then spacetimes

2014 Institute of Physics, Academia Sinica

(Constraint Einstein equation) spacetimes

2014 Institute of Physics, Academia Sinica

Integration by parts: spacetimes

Integration by parts again and dropping the boundary terms:

2014 Institute of Physics, Academia Sinica

2014 Institute of Physics, Academia Sinica spacetimes

2014 Institute of Physics, Academia Sinica spacetimes

2014 Institute of Physics, Academia Sinica spacetimes

5. Related works spacetimes

- Proof for stationary case----in process
- Stability analysis
(1) Z.Roupas [Class. Quantum Grav. 30, 115018 (2013)] calculated the second variation of entropy, showing that the stability of thermal equilibrium is equivalent to stability of Einstein’s equations.

(2) Wald et. al. [Class. Quantum Grav. 31 (2014) 035023 ] proved the equivalence of dynamic equibrium and thermodynamic equibrium for stationary asymtotically flat spacetimes with axisymmetry.

- Beyond general relativity:
Li-Ming Cao, Jianfei Xu, Zhe Zeng [Phys. Rev. D 87, 064005 (2013)] proved the maximum entropy principle in the framework of Lovelock gravity.

2014 Institute of Physics, Academia Sinica

6. Conclusions spacetimes

- We have rigorously proven the equivalence of the extrema of entropy and Einstein's equation under a few natural and necessary conditions. The significant improvement from previous works is that no spherical symmetry or any other symmetry is needed on the spacelike hypersurface. Our work suggests a clear connection between Einstein's equation and thermodynamics of perfect fluid in static spacetimes.

2014 Institute of Physics, Academia Sinica

Thank you! spacetimes

2014 Institute of Physics, Academia Sinica

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