On the thermodynamics of moving bodies

We model the situation in which a photon detector moves with constant velocity in a Minkowski heat-bath by considering an Unruh-DeWitt detector, with variable energy gap ℏω, moving on a brane, at a non-zero (Unruh) temperature T due to acceleration in an orthogonal direction. We compute the angular response for a 2-brane. At low velocity we find agreement with the standard Doppler shift formula in the limit ℏω T in which the photon gas is classical; otherwise there is a discrepancy. At relativistic velocities our result disagrees with the standard formula even when ℏω T, and above a critical velocity there is no response from the detector within a 'backward' cone. We discuss potential implications for observations of the cosmic microwave background radiation. [Talk given by JGR at this 1st Mediterranean Conference in Classical and Quantum Gravity].