Unruh Radiation

Physicist J. Bekenstein determined that a particle accelerating in a vacuum experiences a blackbody radiation bath around itself at a temperature directly proportional to its acceleration. By the equivalence principle, would a particle at rest in a gravitational field also experience this blackbody radiation bath?

Answer

The Equivalence Principle tells us that a particle accelerating in the vacuum is equivalent to a particle at rest in a uniform gravitational field. If there is radiation in one case, there must be radiation in the other equivalent case. The former is called Bekenstein radiation, the latter Unruh radiation, named after physicists who studied the properties of the radiation theoretically. No one has ever measured this radiation because its intensity is many powers of 10 too faint to be detected.