Unruh effect

The prediction that an observer accelerating through a quantum field perceives a thermal bath, even when inertial observers see the vacuum. Its temperature is proportional to the observer’s proper acceleration.

Rindler coordinates: Coordinates adapted to uniformly accelerated observers in flat spacetime. They describe the observer’s trajectory and the horizon that separates accessible field modes.
Quantum field theory: A framework describing particles as excitations of fields that extend throughout spacetime. The effect arises from how observers define excitations of quantum fields.
William Unruh: Canadian theoretical physicist known for predicting the thermal response of uniformly accelerated observers. His 1976 analysis established the effect now bearing his name.
Unruh–DeWitt detector: An idealized pointlike quantum system coupled to a field to model particle detection. Its excitation probability provides a precise way to calculate what an accelerated observer detects.
Experimental detection of the Unruh effect: The effort to measure radiation or detector excitation caused by acceleration through a quantum field. Large accelerations are needed for appreciable temperatures, making direct tests challenging.
Rindler horizon: A causal boundary beyond which events cannot send signals to a uniformly accelerated observer. It divides the field into accessible and inaccessible regions, underlying the observer’s thermal description.
Proper acceleration: The acceleration measured by an object’s instantaneous rest-frame accelerometer. It sets the temperature perceived in the Unruh effect.
Stephen Hawking: British theoretical physicist who predicted thermal radiation from black holes. Work on black-hole radiation formed the setting in which Unruh developed the observer-based result.
Hawking–Unruh correspondence: The relation between thermal effects caused by black-hole horizons and those caused by observer acceleration. The Unruh effect supplies a flat-spacetime comparison for interpreting Hawking radiation.
Dynamical Casimir effect: The production of real photons when a boundary condition changes rapidly in time. It offers an experimentally accessible acceleration-related phenomenon, but is not itself the Unruh effect.

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