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Quarkroscoe
2018-Mar-12, 07:31 PM
As photons travel from the CMB to Earth, they are red shifted from visible light into microwave wavelengths. Since visible light is more energetic than microwaves, were did the energy go?

antoniseb
2018-Mar-12, 08:07 PM
If you were traveling in the same frame of reference as the source of the CMB, you'd still see it in the ultraviolet. No energy was lost.

Ken G
2018-Mar-12, 08:35 PM
As photons travel from the CMB to Earth, they are red shifted from visible light into microwave wavelengths. Since visible light is more energetic than microwaves, were did the energy go?Energy is always only conserved in a single frame, not if you change frames. For example, if a baseball is thrown backward from a car, the ball might have zero speed relative to the road-- so where did the energy that the thrower put into it go?

George
2018-Mar-12, 08:58 PM
Energy is always only conserved in a single frame, not if you change frames. For example, if a baseball is thrown backward from a car, the ball might have zero speed relative to the road-- so where did the energy that the thrower put into it go?If my brother threw it, it would go to increase the car's speed. ;) [He wasn't very accurate, thankfully, since he, when highly agitated, couldn't hit me with his rocks.]

Ken G
2018-Mar-13, 12:59 AM
If my brother threw it, it would go to increase the car's speed. If you stay in the same frame, energy is conserved. I'm talking about after the ball is released, in the car's frame it has a lot of energy and the car has none. Go to the road frame, the ball has no energy, but the car does not make up the difference (it has gobs of energy!).

cjameshuff
2018-Mar-13, 01:29 AM
Locally, energy is still conserved. Globally, energy isn't conserved in GR, because the geometry of the space-time that you are measuring energy within can change. The product of energy*momentum is conserved, though.

http://www.preposterousuniverse.com/blog/2010/02/22/energy-is-not-conserved/

Quarkroscoe
2018-Mar-13, 05:22 PM
cjameshuff...I can get my armes around this explanation. It also matches what Lawrence Krauss said in one of his recent lectures.