# Where does the energy of light go, when it red-shifts?

When talking about the expansion of the universe, it is said that it can be proven by the red-shifting of light.(As we would need higher than lightspeed to get this redshift by the Doppler effect)

I am an amateur, so I am not sure I am correct, but here is what I think.

Redshifting increases the wavelength of the light. higher wavelength = lower frequency = less energy.

So, if my assumptions are correct, where does this energy from the light go? If not, where did I make an incorrect assumption?

• This was answered here great question though. Oct 7, 2016 at 2:24