By invoking inverse temperature as a van Kampen-Israel future-directed timelike 4-vector, this paper derives the Relativistic Blackbody Spectrum, the Relativistic Wien's Displacement Law, and the Relativistic Stefan-Boltzmann Law in inertial and non-inertial reference frames. 2 Significant misperceptions have arisen concerning temperature in relativistic thermodynamics due in part to the confusion surrounding the respective differences between empirical and absolute temperatures. The empirical temperature is a Lorentz invariant, relativistic scalar that considers the radiation rest frame and the observer frame to be in thermal equilibrium [22]. This ensues from the Zeroth Law of Thermodynamics, and correlates directly to the absolute temperature in the radiation (source) frame. The Zeroth Law's validity is required without making use of any thermodynamic property (including entropy and energy) [23].The absolute temperature of a thermodynamic system is a consequence of the Second Law of Thermodynamics. It is the product of the Lorentz factor and the absolute temperature in the radiation frame, and contains no angular dependence. Even though the difference between empirical and absolute temperatures may be observable in nonrelativistic thermodynamics, it becomes persuasively illuminated in relativistic thermodynamics.The Planck distribution describes a solid angular photon number density, and defines a directional (or effective) temperature. However, this results from solely mathematical manipulations, and its thermodynamic relevance is, at best, questionable. Alternatively, temperature transformations can be accomplished by treating inverse temperature as a van Kampen-Israel future-directed timelike 4-vector. Although Przanowski and Tosiek [24] i , and Lee and Cleaver [4] ii have demonstrated temperature inflation without making use of inverse temperature, angular dependence is required for the relativistic blackbody spectrum.
Derivation of the Relativistic Spectral RadianceThe relativistic blackbody spectrum can be obtained by considering the blackbody spectrum of a stationary radiation source, and including temperature inflation (in terms of inverse temperature), Doppler shifting, and relativistic beaming. The inertial and non-inertial frames cases are each examined. In the non-inertial case, the Unruh Effect is not considered because it is many orders of magnitude smaller than the effect presented here.
Inertial FramesThe radiation (source) frame photon energy density ε in frequency and wavelength spaces of a Planckian distribution are: