eli5 So if the universe is constantly expanding and there is no void then what happens to light? Does it just get to the furthest expansion and wait for it to expand more? Does the expansion of the universe “stretch” light enough where it loses too much energy and stops?

Question

Basically, where does light end up? I know that there is no void and that the universe is all that there is and it is constantly expanding, but what happens to light? Wouldn’t it reach the edge? Does cosmological redshift eventually cause the light to stop after long enough?

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Answer 1

Universe isnt expanding at the “edges”, edges probably dont even exist, its expanding universally across its whole surface and volume. Its basically stretching.

And even the universe where our earth is, is being stretched in between you and me, but gravitational and other forces keep us together, so we dont notice it. But other celestial bodies that dont have any interaction between each other are getting further apart. Universe is being stretched everywhere, all at once.

And like someone already said here, it’s stretching faster than the speed of light, so light cant outrun it.
And we dont know but, most probably universe doesnt even have a limit, and it could even be curved in such a way that you just end up in the same place if you go far enough, like its circular in a way.

So a beam of light wouldnt reach the “edge” of the universe, it would just circle back around to where it originated from, and would keep doing that forever, until something stops it.