(December 2, 2015 at 5:28 pm)Quantum Wrote: Mass is simply the measure of how much energy of any form is contained in an object (*). Energy is conserved at short time spans, but can be converted and in particular, energy which appears as mass, can be freed from its confines and converted into other types. However, cosmic expansion removes energy from the universe via the redshift.
(*) This holds always. For example, a spring under tension has more mass than a relaxed one, precisely differing by the stored energy divided by c^2
I thought Friedman equations shows energy is conserved in the entire expanding universe despite the red shifting of the photons.
