This question has arisen from a wish to understand an end-of-universe scenario: heat death.
Are time and mass intrinsically linked?
If so, does time "run slower" (whatever that may mean) in a universe with less mass? And ultimately, in a universe without any mass, just space and energy (photons), then the universal clock stops ticking. I.e. no further aging takes place?
So does time slow down gradually as baryonic mass breaks down?
If this is the case, would the rate at which time slows down also slow down - because time itself as slowed down - leading to an asymptotic decay of time. I.e. it would take forever for all the particles to decay because each particle takes longer and longer to break down due to time slowing down.