eli5: Does expansion of the universe not cause reduction in mass and energy? How does does the mass and energy of an expanding universe remain constant and not reduce or diffuse?

Question

eli5: Does expansion of the universe not cause reduction in mass and energy? How does does the mass and energy of an expanding universe remain constant and not reduce or diffuse?

In: 279

Answer 1

oh mass and energy in the universe remain constant overall but if you consider at a point it’ll be ‘running thin’ as they keep expanding. This is a concept known as heat death where things are so far from each other, energy and mass becoming so thin that everything stops and no process can proceed further since there’s not enough energy at that point of process.