Do particles still have gravitational potential energy if they are trapped in their own light cones; isolated from everything else (eg. when space has sufficiently expanded)? Surely GPE only exists when a particle is in relation to other particles...?
I was thinking specifically in terms of Roger Penrose's conformal cyclic cosmology. In his hypothesis mass is required to eventually decay over time. I wondered whether it is plausible that instead of mass decaying, all motion stops at the heat death and then there is no more mass.
I've been thinking about mass and the question occurred to me: If a particle is completely inert i.e. absolutely no motion whatsoever then does it still have a mass? I ask because, as far as I understand it, everything we've ever measured cannot strictly be said to be inert. That is: Every...