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

You’re on the right track. The amount of matter and energy will remain the same and more ‘space’ is created as the universe expands. One possible outcome of this would be the ‘heat death’ of the universe.

Edit
In places like galaxies, gravity also counteracts the expansion of space. Most of the expansion happens in the emptier areas between gravity wells.