Where Did the Energy Go in Light Waves When the Universe Expanded?

[Daniel Petka]

https://www.physicsforums.com/attachments/198775

The expansion of the universe stretches the wavelength of EM-waves. Though the energy equivalence says energy can't be destroyed... so where did the energy go?

 

[Drakkith]

Though the energy equivalence says energy can't be destroyed...

That's not energy equivalence, it's the conservation of energy law. Conservation of energy doesn't apply to the universe as a whole, it only applies locally.

 

[Daniel Petka]

1.)Lol that's what I meant sorry
2.)What exactly do you mean by saying locally?

 

[Drakkith]

I'm not sure about the technical definition of local, but I believe the idea is that it's a small region of space where things like the curvature of spacetime is negligible and the laws of special relativity can be used.

For more info on this topic, see this link: http://math.ucr.edu/home/baez/physics/Relativity/GR/energy_gr.html

 

[Daniel Petka]

Thanks that helped