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

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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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22 Answers

Anonymous 0 Comments

Because it’s not infinite in time. Light takes time to travel, and the universe as we know it has a beginning. So there is some distant location from which light from the earliest moment could just now be reaching us. The current distance to that location defines the “observable universe”.

Anonymous 0 Comments

>hence the light from the farthest will take billions of years to reach us

This is why.

We can only see as far as the farthest objects whose light has had time to reach us. The universe is about 13.7 billion years old, so we can only see things whose light has traveled 13.7 billion years to get to us. Anything farther away and light hasn’t had enough time to reach us yet

The universe is also expanding, in the sense that space itself is stretching out. That’s its own ELI5, but the consequences here are 1) the light that traveled 13.7 billion light years to reach us actually started closer, because the distance got bigger as it was traveling and 2) some things we can never observe because they’re moving away from us faster than light, so the light will never be able to catch up to us.

Anonymous 0 Comments

I don’t understand the question, but if your asking why we can’t see the big bang, it’s because our telescopes sent good enough yet… but they are getting close. If you’re asking why we can’t see the edge of the universe, it’s Because the universe is expanding faster than the speed of light. it’s doing this faster than the speed of light and not breaking any other rules of physics because new space is being formed between the stars … the universe is literally growing between galaxies.

Anonymous 0 Comments

I’m not sure I understand your question. I’ll answer it and you can tell me whether I guessed correctly.

Our ability to see is limited by our telescopes or other devices for increasing our perceptions. It used to be just based on what we could see with our bare eyes. Telescopes keep improving, but even the new James Webb Space Telescope, which has greatly increased our ability to see distant stars, doesn’t allow us to see all of them.

Of course, even the stars we can see have been moving away from us even as their light moved toward us. So the ones on the outer edge of our sight have now moved out of our sight. We can calculate how far they would be now, but we can no longer see them with the telescopes we have.

Anonymous 0 Comments

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.

Anonymous 0 Comments

> I understood that there was nothing in the beginning and everything was formed all at once

We don’t know what was there “before the big bang” (which is already ill defined because the big bang is the beginning of time as we know it), but having the universe being created ex-nihilo creates more problems than solves.

So there most probably was something that caused the Big Bang, the universe as it is today probably didn’t just “appear out of nothing”. What that was and what laws of physics did it obey? Was there time, the way we describe and think about it now? Maybe, maybe not.

But “we don’t know” is a far cry away from “there was nothing”.

Regarding the rest of your question, I don’t know, but we can’t actually see light as far back as the big bang, because the universe was opaque at the time and no light from before then has been allowed to reach us without being intercepted by something else.

The first time this has happened is at so called recombination, which happened ~380,000 years after the big bang. At that point the universe was infinite and since light travels at a finite speed, we can’t see further away than that.

As time goes by, light from the moment of recombination we see comes from further and further away, because more and more time has passed.

That’s why we can only see a finite part of the universe and it’s getting bigger as time goes by.

Anonymous 0 Comments

This is a variant on Olbers’ paradox: if the universe is infinite, why is it dark at night?

Anonymous 0 Comments

We actually don’t know if the universe is infinite or not.

We noticed that galaxies tend to all be moving further apart from each other over time. If you play time in reverse, they appear to be getting closer together. And we’re able to play time in reverse because light takes a long time to reach us if it’s coming from really far away. So when we observe stuff that’s really far away it’s like looking far into the past.

But…. There is stuff that is soooo far away that the light will never reach us because the space between us is expanding faster than the light can travel the distance. Anything past this distance has exited the observable universe and we can no longer see it forever.

Thus, the observable universe has a finite distance that can be measured and is not infinite. We can only observe stuff that light can travel the distance between faster than the space expands.

But everything outside the observable universe? We’re not entirely sure how big that is. Could be infinite, might not be infinite. We don’t have a way to prove it yet.

There is the cosmic microwave background radiation which is light that appears everywhere and thus seems to be good evidence for a big bang type event (since if everything originated at a single point that would explain the light being everywhere). But that doesn’t tell us if the universe is infinite or not (what if the single point was infinite).

Anonymous 0 Comments

Because it’s not infinite in time. Light takes time to travel, and the universe as we know it has a beginning. So there is some distant location from which light from the earliest moment could just now be reaching us. The current distance to that location defines the “observable universe”.

Anonymous 0 Comments

>hence the light from the farthest will take billions of years to reach us

This is why.

We can only see as far as the farthest objects whose light has had time to reach us. The universe is about 13.7 billion years old, so we can only see things whose light has traveled 13.7 billion years to get to us. Anything farther away and light hasn’t had enough time to reach us yet

The universe is also expanding, in the sense that space itself is stretching out. That’s its own ELI5, but the consequences here are 1) the light that traveled 13.7 billion light years to reach us actually started closer, because the distance got bigger as it was traveling and 2) some things we can never observe because they’re moving away from us faster than light, so the light will never be able to catch up to us.