# Macroscopic aspects of the Unruh effect

December 18, 2014

Macroscopic concepts pertaining to the Unruh effect are elaborated and used
to clarify its physical manifestations. Based on a description of the motion of
accelerated, spatially extended laboratories in Minkowski space in terms of
Poincar\'e transformations, it is shown that, from a macroscopic perspective,
an accelerated observer will not register with his measuring instruments any
global thermal effects of acceleration in the inertial (Minkowskian) vacuum
state. This result is not in conflict with the well-known fact that microscopic
probes respond non-trivially to acceleration if coupled to the vacuum. But it
implies that this response cannot be interpreted as the effect of some heat
bath surrounding the observer. It is also shown that genuine equilibrium states
in a uniformly accelerated laboratory are not spatially homogeneous. In
particular, all equilibrium states coincide with the inertial vacuum at
sufficiently large distances from the horizon of the observer and consequently
have the same (zero) temperature there. The analysis is carried out in the
theory of a free massless scalar field, but its conclusions hold more
generally.

Keywords:

*none*