Abstract

In 1974, Hawking showed^1,2 that black holes evaporate by the emission of low-temperature thermal radiation, now named Hawking radiation. Shortly thereafter a closely related effect called Unruh radiation became apparent. According to Unruh³ and Davies,⁴ observers of the electromagnetic field in an accelerating reference frame should see thermal radiation at a temperature T: where a is the acceleration relative to an inertial frame, c is the speed of light, and ħ and k are Planck's and Boltzmann’s constant, respectively. With an acceleration equivalent to that at the earth’s surface, g = 980 cm/s², this thermal radiation is at a temperature of only 4 × 10⁻²⁰ K. Bell has suggested⁵ that the spin depolarization of electrons accelerating around a storage ring may be interpreted as being caused by such radiation. Boyer⁶ introduced a physically helpful semiclassical interpretation of Unruh radiation. In his phe­nomenological picture, external zero point electro-magnetic field fluctuations are accelerated up to a nonzero temperature. The observer need not experience the acceleration directly. Davies and Fulling⁷ argued that the observation of reflected zero point field fluctuations from an accelerating mirror was sufficient to establish the relative accelerating motion.

© 1988 Optical Society of America