Thread: Confusion about Redshift due to Universal Expansion

Hello, I am currently halfway through a physics undergrad, and have a question that I can't really find an answer to.The expansion of the universe clearly causes a redshift different from the Doppler Effect. The specifics of this redshift, as far as I can tell, are explained through General Relativity.My question is that if all of these photons are being redshifted due to this expansion, where is the photon energy going? It seems like this universal redshift of light must be indicative of some sort of universal energy loss. Can anyone address this question? Thanks!

I'm no physics major but from what I understand, the redshift is caused by the stretching of the light waves. Im not sure how this would result in any energy loss.