A new look at relativistic thermodynamics

The Lorentz transformations of special relativity (SR) convert time or distance intervals from a resting frame of reference to one that is moving, even at nearly the speed of light. But what temperature will a speeding observer register for a gas in a stationary bottle? A closely related question concerns the correct generalization of Maxwell’s velocity distribution to SR, in which more energy means more mass and nothing can move faster than the speed of light. The first answer was put forth by Ferencz Jüttner in 1911, and many variations on his theme have appeared since the 1980s. It is very difficult to maintain a contained gas at relativistic speeds in a terrestrial laboratory, but Jörn Dunkel and his colleagues at the University of Augsburg (Germany) and the University of Seville (Spain) have now performed extensive simulations for a one-dimensional, fully relativistic, two-component gas. The results unequivocally favor the original Jüttner distribution. Furthermore, the simulations illustrate that the concepts of thermal equilibrium and temperature can extend to SR only for spatially confined systems. And, measured with a velocity-based statistical thermometer, moving bodies appear neither hotter nor colder than stationary ones. (D. Cubero et al., Phys. Rev. Lett. 99 , 170601, 2007 http://dx.doi.org/10.1103/PhysRevLett.99.170601 .)