The Planck Blackbody Spectrum Follows from the Structure of Relativistic   Spacetime
  Here we show that within classical physics, the Planck blackbody spectrum can be derived directly from the structure of relativistic spacetime. In noninertial frames, thermal radiation at positive temperature is connected directly to zero-point radiation whose spectrum follows from the geodesic structure of the spacetime. The connection between zero-point radiation and thermal radiation at postive temperature is through a time-dilating conformal transformation in the noninertial frame. Transferring the spectrum back to Minskowski spacetime, the Planck spectrum is obtained. 
Timothy H. Boyer
physics.class-ph