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What is the entropy of the universe?

Paul H Frampton1, Stephen D H Hsu2, Thomas W Kephart3 and David Reeb2

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Standard calculations suggest that the entropy of our universe is dominated by black holes, whose entropy is of order their area in Planck units, although they comprise only a tiny fraction of its total energy. Statistical entropy is the logarithm of the number of microstates consistent with the observed macroscopic properties of a system, hence a measure of uncertainty about its precise state. Therefore, assuming unitarity in black hole evaporation, the standard results suggest that the largest uncertainty in the future quantum state of the universe is due to the Hawking radiation from evaporating black holes. However, the entropy of the matter precursors to astrophysical black holes is enormously less than that given by area entropy. If unitarity relates the future radiation states to the black hole precursor states, then the standard results are highly misleading, at least for an observer that can differentiate the individual states of the Hawking radiation.


PACS

98.80.Cq Particle-theory and field-theory models of the early Universe (including cosmic pancakes, cosmic strings, chaotic phenomena, inflationary universe, etc.)

04.70.Dy Quantum aspects of black holes, evaporation, thermodynamics

95.30.Tg Thermodynamic processes, conduction, convection, equations of state

97.60.Lf Black holes

MSC

83C57 Black holes

83F05 Cosmology

Subjects

Gravitation and cosmology

Astrophysics and astroparticles

Dates

Issue 14 (21 July 2009)

Received 5 February 2009, in final form 7 April 2009

Published 19 June 2009



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