PHD Discussions Logo

Ask, Learn and Accelerate in your PhD Research

Question Icon Post Your Answer

Question Icon

10 months ago in Cosmology By Akash

Where did the cmb’s energy go?

The cosmic microwave background started as a hot, dense, high-energy soup. Today it's cold and faint. Where did all that energy go?

All Answers (1 Answers In All)

By Shraddha Answered 7 months ago

It didn't vanish it redshifted away. As the universe expands, the wavelengths of CMB photons stretch. Longer wavelength means lower frequency, lower energy per photon (E = hf). The total energy density of the radiation field decreases because space itself has grown. But energy is not lost without a trace; in General Relativity, that energy does work against the gravitational pull of the universe. It's accounted for. It's just not where it started.

Your Answer