Thermodynamics of Spacetime: The Einstein Equation of State
Abstract
The Einstein equation is derived from the proportionality of entropy and the horizon area together with the fundamental relation δQ = T dS. The key idea is to demand that this relation hold for all the local Rindler causal horizons through each spacetime point, with δQ and T interpreted as the energy flux and Unruh temperature seen by an accelerated observer just inside the horizon. This requires that gravitational lensing by matter energy distorts the causal structure of spacetime so that the Einstein equation holds. Viewed in this way, the Einstein equation is an equation of state.
 Publication:

Physical Review Letters
 Pub Date:
 August 1995
 DOI:
 10.1103/PhysRevLett.75.1260
 arXiv:
 arXiv:grqc/9504004
 Bibcode:
 1995PhRvL..75.1260J
 Keywords:

 General Relativity and Quantum Cosmology;
 High Energy Physics  Theory
 EPrint:
 8 pages, 1 figure. Revised version has core unchanged but paper rewritten and expanded to clarify the reasoning and to emphasize some points. One figure added