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What is the entropy in entropic gravity?

Sean M. Carroll* and Grant N. Remmen†

  • Walter Burke Institute for Theoretical Physics, California Institute of Technology, Pasadena, California 91125, USA

  • *seancarroll@gmail.com
  • †gremmen@theory.caltech.edu
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Phys. Rev. D 93, 124052 – Published 21 June, 2016

DOI: https://doi.org/10.1103/PhysRevD.93.124052

Abstract

We investigate theories in which gravity arises as a consequence of entropy. We distinguish between two approaches to this idea: holographic gravity, in which Einstein’s equation arises from keeping entropy stationary in equilibrium under variations of the geometry and quantum state of a small region, and thermodynamic gravity, in which Einstein’s equation emerges as a local equation of state from constraints on the area of a dynamical light sheet in a fixed spacetime background. Examining holographic gravity, we argue that its underlying assumptions can be justified in part using recent results on the form of the modular energy in quantum field theory. For thermodynamic gravity, on the other hand, we find that it is difficult to formulate a self-consistent definition of the entropy, which represents an obstacle for this approach. This investigation points the way forward in understanding the connections between gravity and entanglement.

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Phys. Rev. D 93, 124052– Published 21 June, 2016
  • Received 29 January 2016
Article part of CHORUS

© 2016 American Physical Society

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