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Where Does the Energy Loss Due to Redshift Go in an Expanding Universe?

-- robbie | February 9, 2020

Cosmic Microwave Background Radiation Animation

Question:

Hello Jeff

If light is redshifted in an expanding universe, and this results in photons losing energy, where does that energy go to?

Thanks, Robbie

-- robbie

Answer:

Let me refer you to an Ask Ethan blog post which provides an excellent detailed answer to your question. The short answer, though, is that light loses energy as the Universe expands, and that energy goes into the expansion of the Universe itself, in the form of work.

-- Jeff Mangum

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