Unruh effect

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The Unruh effect (also known as the Fulling–Davies–Unruh effect) is a hypothetical, observer-dependent prediction of quantum field theory that an observer who is uniformly accelerating through empty space (Minkowski vacuum) will perceive a thermal bath. This means that even in the absence of any external heat sources, an accelerating observer will detect particles and experience a temperature. In contrast, an inertial observer in the same region of spacetime would observe no particles and no temperature. In other words, the background appears to be warm from an accelerating reference frame. In layman's terms, an accelerating thermometer in empty space (like one being waved around), without any other contribution to its temperature, will record a non-zero temperature, just from its acceleration. Heuristically, for a uniformly accelerating observer, the ground state of an inertial observer is seen as a mixed state in thermodynamic equilibrium with a non-zero temperature bath. The Unruh effect...

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