Recoil of rotating detector

The question of why rotating detectors may respond even in the appropriate vacuum defined via canonical quantization has been a puzzle. We solve this puzzle by taking the recoil of the detector into account. The influence of the recoil, even in the limit of an infinite mass detector, appears in the response function. This enables the detector to respond in the vacuum if it is rotating, though in linear uniform motion it never responds in the vacu um, as is expected from Poincare invariance.