Why is the universe limited in range of visibility if it is infinite?

Question

Please correct me if I’m wrong in understanding big bang, I understood that there was nothing in the beginning and everything was formed all at once, hence the light from the farthest will take billions of years to reach us to see it’s present moment and so why is matter limited, honestly feels like a computer simulation since everything is limited in nature.

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Answer 1

First: we don’t actually know what went on *at* the big bang. We can get very close to it and still know what’s going on, but we don’t know what happened *at* the moment of, or what happened before (if “before” really even applies… it gets weird).

So we don’t know why only so much energy is in the universe. But the fact that only so much energy is in the universe is the reason why matter is limited–matter is basically frozen energy, so limited energy means limited matter.

As for why the range of visibility is limited? Shortly after the big bang, the universe underwent a period of inflation. It’s still inflating, actually, but it was inflating *much* more rapidly back then. This means that things raced away from each other at much faster than the speed of light. The speed of light (which is really the speed of cause-and-effect) only applies to things moving *through* space; it doesn’t apply to space itself. When things got distant enough, even when the inflation slowed down, they were so far away that even the reduced inflation is carrying them away from each other at faster than the speed of light (because, technically, they’re not moving *through* space. Space is expanding between them, causing them to effectively move away from each other, but it’s a very different thing).

Since those things are moving away from us faster than the speed of light, light that they emit can never reach us. The section of the universe that we call the “observable” universe is literally that: it’s the part of the universe that, given enough time, light from any point in that area can reach us, and we can observe it. Light from outside that region can *never* reach us, so we can never observe it.