Thermodynamical interpretation of the second law for cosmology

Abstract

The area of a future holographic screen increases monotonically. This area can be associated with entropy, resulting in a generalized second law for cosmology (GSLC). However, such an area law has no thermodynamical interpretation, in contrast to black hole horizons. We propose a thermodymical interpretation by relating the screen area to a phase space by means of a geometrical construction. This enables us to uniquely identify the direction of foliation necessary in order to present the entropy of any holographic screen as entropy derived from phase space. Moreover, by construction, this allows us to associate a specific temperature with each holographic screen. In the case of accelerated observers, these quantities coincide with the entropy and temperature that they detect due to their acceleration. Thus, using the equivalence principle, we obtain a thermodynamical interpretation for the GSLC.