Thermal nature of de Sitter spacetime and spontaneous excitation of atoms

TL;DR

This paper demonstrates that atoms in de Sitter spacetime experience spontaneous excitation akin to being in a thermal bath, confirming the thermal nature of de Sitter space through quantum field interactions.

Contribution

It provides a detailed analysis of spontaneous atomic excitation in de Sitter spacetime, linking vacuum fluctuations and radiation reaction to thermal effects, extending Gibbons and Hawking's results.

Findings

Freely falling atoms perceive a thermal bath at Gibbons-Hawking temperature.

Static atoms also perceive a thermal bath due to spacetime's intrinsic temperature and acceleration effects.

Spontaneous excitation occurs even without external radiation, confirming the thermal nature of de Sitter space.

Abstract

We consider, in de Sitter spacetime, both freely falling and static two-level atoms in interaction with a conformally coupled massless scalar field in the de Sitter-invariant vacuum, and separately calculate the contributions of vacuum fluctuations and radiation reaction to the atom's spontaneous excitation rate. We find that spontaneous excitations occur even for the freely falling atom as if there is a thermal bath of radiation at the Gibbons-Hawking temperature and we thus recover, in a different physical context, the results of Gibbons and Hawking that reveals the thermal nature of de Sitter spacetime. Similarly, for the case of the static atom, our results show that the atom also perceives a thermal bath which now arises as a result of the intrinsic thermal nature of de Sitter spacetime and the Unruh effect associated with the inherent acceleration of the atom.