Cosmology with Negative Absolute Temperatures

TL;DR

This paper explores the cosmological implications of negative absolute temperature systems, suggesting they could lead to novel universe expansion behaviors and offer alternative solutions to classical cosmological problems.

Contribution

It investigates the potential role of NAT in cosmology, proposing new models for universe expansion and contraction, and discusses their feasibility and implications.

Findings

NAT-dominated universes exhibit borderline phantom expansion without Big Rip.

Contracting NAT universes are forced to bounce at high energy densities.

NAT scenarios could provide alternative solutions to horizon and flatness problems.

Abstract

Negative absolute temperatures (NAT) are an exotic thermodynamical consequence of quantum physics which has been known since the 1950's (having been achieved in the lab on a number of occasions). Recently, the work of Braun et al (2013) has rekindled interest in negative temperatures and hinted at a possibility of using NAT systems in the lab as dark energy analogues. This paper goes one step further, looking into the cosmological consequences of the existence of a NAT component in the Universe. NAT-dominated expanding Universes experience a borderline phantom expansion ($w<-1$) with no Big Rip, and their contracting counterparts are forced to bounce after the energy density becomes sufficiently large. Both scenarios might be used to solve horizon and flatness problems analogously to standard inflation and bouncing cosmologies. We discuss the difficulties in obtaining and ending a NAT-dominated epoch, and possible ways of obtaining density perturbations with an acceptable spectrum.