The observable universe. Does it mean the edge of space where nothing else is? Is it where the universe is currently at in its expansion after the big bang? Or is it just a barrier that our telescopes are yet to look beyond, and there are just more galaxies past it?
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Its the furthest distance that light has had time to reach us.
So we might look at a star very faintly whose light started traveling to us back near the start of the universe.
There will be light sources further away, but their light has not reached us yet.
But it will in time.
So the observable universe is getting bigger at the speed of light.
Note: For two separate things to **cause** an effect on each other, something must travel in between. And the fastest travel is light. So the speed of causality is light speed.
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