Demise of Unruh radiation

Unruh radiation has attracted much interest, particularly because of its relationship to Hawking radiation. But its existence has been challenged by a variety of authors, including ourselves [Phys. Lett. A158, 31 (1991)]. The absence of a consensus may be traced to the complex challenge of dealing with the infinite number of particles of the associated heat bath. Here, we show how this problem may be obviated by using the quantum Langevin equation [Ford et al., Phys. Rev. A37, 4419 (1988); J. Math. Phys.6, 504 (1965)], which enables us to present a simple argument to show that, despite the existence of an Unruh temperature, there is no Unruh radiation. A key point is that the Unruh system is an equilibrium system, in contrast to the Hawking system which is a non-equilibrium system.