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Entropy and Quantum Gravity
Open AccessArticle

Gravitational Entropy and the Second Law of Thermodynamics

Perimeter Institute for Theoretical Physics, Waterloo, Ontario N2L 2Y5, Canada
Department of Physics and Astronomy, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
Academic Editors: Kevin H. Knuth and Remo Garattini
Entropy 2015, 17(12), 8341-8345;
Received: 8 October 2015 / Accepted: 15 December 2015 / Published: 21 December 2015
(This article belongs to the Special Issue Entropy in Quantum Gravity and Quantum Cosmology)
The spontaneous violation of Lorentz and diffeomorphism invariance in a phase near the big bang lowers the entropy, allowing for an arrow of time and the second law of thermodynamics. The spontaneous symmetry breaking leads to O(3,1) → O(3) × R , where O(3) is the rotational symmetry of the Friedmann–Lemaître–Robertson–Walker spacetime. The Weyl curvature tensor Cμνρσ vanishes in the FLRW spacetime satisfying the Penrose zero Weyl curvature conjecture. The requirement of a measure of gravitational entropy is discussed. The vacuum expectation value 〈0|ψμ|0〉 ≠ 0 for a vector field ψμ acts as an order parameter and at the critical temperature Tc a phase transition occurs breaking the Lorentz symmetry spontaneously. During the ordered O(3) symmetry phase the entropy is vanishingly small and for T < Tc as the universe expands the anti-restored O(3,1) Lorentz symmetry leads to a disordered phase and a large increase in entropy creating the arrow of time. View Full-Text
Keywords: gravitation; cosmology; entropy gravitation; cosmology; entropy
MDPI and ACS Style

Moffat, J.W. Gravitational Entropy and the Second Law of Thermodynamics. Entropy 2015, 17, 8341-8345.

AMA Style

Moffat JW. Gravitational Entropy and the Second Law of Thermodynamics. Entropy. 2015; 17(12):8341-8345.

Chicago/Turabian Style

Moffat, John W. 2015. "Gravitational Entropy and the Second Law of Thermodynamics" Entropy 17, no. 12: 8341-8345.

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