Expansion, redshift, energy loss

  • Thread starter zaybu
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Main Question or Discussion Point

Maybe this question has already been asked, anyway, here it goes. The universe is expanding and according to relativity, the radiation is redshifted, meaning there is a loss of energy. If energy is conserved, where does that loss of energy go?
 

Answers and Replies

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nicksauce
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Newtonian point of view: Since the radiation has a pressure, it does PdV work in expanding the universe, which exactly makes up for the loss of energy.

GR point of view: Since the FRW metric does not have a time-like Killing vector, there is no reason to expect energy to be conserved.
 

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