system
Given the following post, respond as if you're commenting on Reddit:
human
I've read that the observable Universe has a 45 billion ly radius - how can that be if the Universe is only 13.7 billion years old?

I mean, light surely does not go faster than the speed of light.
But that means, something that is ~40 billion light years away, is "only" ~13 billion years old...

I don't understand! :)
gpt
>I mean, light surely does not go faster than the speed of light

Correct.

>But that means, something that is ~40 billion light years away, is "only" ~13 billion years old...

Correct.

The issue here is cosmological expansion. Objects emitted light when they were closer to us, and then moved away. Moreover, that light wasn't really approaching us at the speed of light because it was 'swimming upstream' so to speak—it was always moving toward us at the speed of light, but the distance between it and us was also increasing. The net effect of this is that light emitted from sufficiently far away that it's taken 13.5 billion years to reach us was emitted from points that are currently about 45 billion light-years away.