Accelerating reference frame for electromagnetic waves in a rapidly growing plasma: Unruh radiation and the dynamic Casimir effect

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 Unruh 3 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/s 2 , this thermal radiation is at a temperature of only 4 × 10 −20 K. Bell has suggested 5 that the spin depolarization of electrons accelerating around a storage ring may be interpreted as being caused by such radiation. Boyer 6 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 Fulling 7 argued that the observation of reflected zero point field fluctuations from an accelerating mirror was sufficient to establish the relative accelerating motion.