What happens to potential, thermal, energy in Einsteins equation?
These add to the total mass-energy of the system, and any energy that’s not kinetic “counts” as rest mass. If you add some energy to a system from outside, (and kinetic energy does not increase) the total mass of the system increases. So if, for instance, by some external force you do some work to pull some masses apart, the final system of masses will have more gravitational potential energy, which “counts” as mass of the entire system. Thermal energy of an entire system also counts when considering mass of the entire system (note that kinetic energy in Einstein’s mass-energy equation refers to overall translational energy of the system).
