Gravity's universality: The physics underlying Tolman temperature gradients

Abstract

We provide a simple and clear verification of the physical need for temperature gradients in equilibrium states when gravitational fields are present. Our argument will be built in a completely kinematic manner, in terms of the gravitational red-shift/blue-shift of light, together with a relativistic extension of Maxwell's two column argument. We conclude by showing that it is the universality of the gravitational interaction (the uniqueness of free-fall) that ultimately permits Tolman's equilibrium temperature gradients without any violation of the laws of thermodynamics.

6 pages. 1 figure. First prize essay in the Gravity Research Foundation 2018 Essays on Gravitation. To appear in IJMPD