- #1
nomadreid
Gold Member
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I am sure this question comes up frequently in the forum, and I have read a number of answers to it in different places; namely, that since the expansion of the universe stretches the wavelengths and thereby lowers the energy of light, what happens to the principle of the conservation of Energy? From the answers I have read, it seems that the answer is that Energy is not conserved, as it doesn't obey Noether's Theorem, but that a combination of Energy and stress tensors is what ends up being conserved. However, I doubtful whether this is a good statement of the proper answer. Could someone give me, in relatively straightforward terms (no pun intended), the answer to this question?