It is said that there are extremely distant stars and galaxies that we will never see, because overall, the space between us is expanding faster than their light travels towards us. Does this mean some radiation can travel forever through expanding space, and never reach a mass?
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If light doesn’t reach a mass, its energy is not “lost”. The light itself has energy.
G. Smith
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I do understand your question and your confusion.
Photons are massless particles, they travel along null geodesics, meaning that the spacetime distance between emission and absorption is 0.
You are thinking about information (photon) being emitted somewhere, and then its very purpose should be to receive (absorb) it.
Though, expanding space can somewhat change that, since some photons might never be absorbed, received because the space as you say along their travel direction expands faster then the speed of light. In this case, and I think this is what you mean, this information carried by these photons might never fulfill its purpose. It will never be absorbed, received.
But, the information these photons carry, will not be lost physically. They will just in a way be lost in space, so you are correct. They will never be able to fulfill their very purpose to be received, absorbed.
Yes, the expansion of space itself is allowed to exceed the speed-of-light limit because the speed-of-light limit only applies to regions where special relativity – a description of the spacetime as a flat geometry – applies. In the context of cosmology, especially a very fast expansion, special relativity doesn't apply because the curvature of the spacetime is large and essential.
Árpád Szendrei
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