Stephen A. Fulling - How Acceleration Radiation Respects the Equivalence Principle

Contribution to the Quantum Field Theory in Curved Spacetimes Workshop (23-27 May 2022) https://sites.google.com/view/qftcswo... Author: Stephen A. Fulling Affiliation: Department of Physics and Astronomy, Texas A&M University Title: How Acceleration Radiation Respects the Equivalence Principle Abstract: The emission of quanta by an accelerated detector (Unruh--Wald effect) is in some sense a quantum analog of the classical radiation of photons by an accelerated charge (Larmor effect). The latter has always been controversial. Most experts now agree that a uniformly accelerated charge emits radiation (as seen by a stationary observer), but that it does not radiate from the point of view of a coaccelerated observer (one following another orbit of the same Rindler Killing vector). More controversial is the claim that a stationary charge radiates from the point of view of a uniformly accelerated observer. This effect would be the closest classical analog of the original Unruh effect (the hot vacuum); an even closer quantum analog is the Unruh-like radiation from an atom in free fall into a black hole recently deduced by Scully et al. Moreover, it is demanded by the "qualitative equivalence principle'': Local physics should not depend drastically on whether the force accelerating the charge is gravitational or, say, electromagnetic. The issue is largely one of definition, and its resolution hinges on two distinctions between inertial and accelerated reference frames: (1) For an accelerated observer, energy density and flux must be defined relative to the Rindler (boost) Killing vector field. (2) The Rindler space accessible to that observer is a proper subset of the full Minkowski space. From (1) it has been shown that radiated power depends in a symmetrical way on the accelerations of the charge and the detector (proportional to the square of their difference), as the equivalence principle demands. But the fact that (2) is not symmetrical complicates the ascription of physical reality to the radiation observed by an accelerated detector.