https://doi.org/10.1140/epjc/s10052-021-09028-5
Regular Article – Theoretical Physics
Thermodynamics of the 
Universe: a simplification of cosmic entropy
1
Department of Physics, The Applied Math Program, The University of Arizona, 85721, Tucson, AZ, USA
2
Department of Astronomy, The University of Arizona, 85721, Tucson, AZ, USA
Received:
14
December
2020
Accepted:
5
March
2021
Published online:
16
March
2021
In the standard model of cosmology, the Universe began its expansion with an anomalously low entropy, which then grew dramatically to much larger values consistent with the physical conditions at decoupling, roughly 380,000 years after the Big Bang. There does not appear to be a viable explanation for this ‘unnatural’ history, other than via the generalized second law of thermodynamics (GSL), in which the entropy of the bulk, 
, is combined with the entropy of the apparent (or gravitational) horizon, 
. This is not completely satisfactory either, however, since this approach seems to require an inexplicable equilibrium between the bulk and horizon temperatures. In this paper, we explore the thermodynamics of an alternative cosmology known as the universe, which has thus far been highly successful in resolving many other problems or inconsistencies in 
CDM. We find that 
is constant in this model, eliminating the so-called initial entropy problem simply and elegantly. The GSL may still be relevant, however, principally in selecting the arrow of time, given that 
in this model.
John Woodruff Simpson Fellow.
© The Author(s) 2021
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