Local thermodynamic equilibrium and inertia principle.
The inertia principle states that an object endeavours to preserve its present state. Although we know inertia is the gravitational coupling between matter and spacetime according to general relativity, the detail how this coupling works is not clear because the quantum gravity theory is still an open problem. What will happen if the inertia principle is violated? Here, based on the local thermodynamic equilibrium hypothesis and the relation $\delta Q = T dS$, we obtain the gravitational temperature and entropy of spacetime and matter. Then, we find that a violation of the inertia principle implies a violation of the second law of thermodynamics. What's more, it is the speed limit of light that prevents the gravitational temperature from dropping to absolute zero.
Publisher URL: http://arxiv.org/abs/1801.10018