Unruh versus Tolman: On the heat of acceleration

TL;DR

The paper clarifies that the Unruh effect's temperature increase for accelerated detectors is due to quantum effects from local coupling with the vacuum, not actual heat transfer, and the vacuum remains at zero temperature regardless of acceleration.

Contribution

It demonstrates that the Unruh effect does not imply a real thermal heat exchange, contrasting with Tolman's law, and attributes the temperature readings to quantum vacuum excitations.

Findings

Unruh temperature arises from quantum effects, not heat transfer.

Vacuum remains at zero temperature regardless of acceleration.

The effect is due to local quantum coupling, not thermal energy exchange.

Abstract

It is shown that the Unruh effect, i.e. the increase in temperature indicated by a uniformly accelerated thermometer in an inertial vacuum state of a quantum field, cannot be interpreted as the result of an exchange of heat with a surrounding gas. Since the vacuum is spatially homogeneous in the accelerated system its temperature must be zero everywhere as a consequence of Tolman's law. In fact, the increase of temperature of accelerated thermometers is due to systematic quantum effects induced by the local coupling between the thermometer and the vacuum. This coupling inevitably creates excitations of the vacuum which transfer energy to the thermometer, gained by the acceleration, and thereby affect its readings. The temperature of the vacuum, however, remains to be zero for arbitrary accelerations.