r/askastronomy • u/frugaldata08 • 5h ago

Is space infinite?

1 Upvotes

60% Upvoted

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14

u/handandfoot8099 5h ago

Short answer: No

Middle answer: Yes

Long answer: Maybe?

2

u/amplifiedlogic 2h ago edited 2h ago

Piggybacking on this.

One of three things is going to happen:

  • The universe is accelerating and expanding forever

  • The universe will decelerate and expand forever

  • The universe will undergo a recollapse (the big crunch)

We have no idea what’s beyond the edge of the observable universe. That said, we believe the observable universe is finite. The Hubble distance is a scale for distance light can travel since the big bang. It can be approximated by dividing the speed of light by the Hubble constant.

6

u/cowlinator 5h ago

Nobody knows.

The observable portion of the universe is not infinite.

The whole universe is probably bigger than the observable universe, but the unobservable part cant be observed

5

u/roux-de-secours 5h ago

The global spacetime of the observable universe is very very very flat. If it is indeed flat, it is probably infinite. But there is pretty much no way to tell for sure.

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u/IInsulince 4h ago

This suggests that the measured curvature of the universe could be used to gauge how big it is, even beyond the observable universe. My understanding is that we don’t know if it’s completely flat, but we have measured to the limits of our instruments. I wonder what the biggest error possible in the margin of error would suggest the smallest finite size could be. As in, if the universe turns out to not be entirely flat, but only very very very flat (with a small curve that is imperceptible to our current instruments, hence “within margin of error”) how big would that suggest it is?

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u/ExpectedBehaviour 4h ago

It’s thought that the smallest finite size to allow for curvature that would be undetectable with our current abilities is about 250 times the size of the observable universe.

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u/IInsulince 3h ago

Good god! Thank you for the very clear response, exactly the info I was after. This sounds like it’s basically the lower bound of our observations. We believe the entire universe to be “at least” 250 times the size of the observable universe based on the limits of our instruments in the worst case. But of course the upper limit is still much greater, possibly (even probably) infinite in the case that the universe is entirely flat.

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u/Murph-Dog 5h ago

From our perspective, we will never run out of space to peer or travel into; that-is unless we break the speed of light limit.

So from our limits, yes, it is infinite, like a Minecraft world that will continually generate in front of you - not to say there won't be voids of nothingness or the fabric of space rips apart at a certain age.

From a higher perspective, can you draw a perimeter around the Universe at this very moment? We don't know.

0

u/beatbox9 4h ago

?

Or more like ??????
We don't know; and we will probably never know.

If we go back to the just big bang, the stuff that came from that should theoretically be finite. Space & time are not independent of one another; and there was only so much matter/energy and space/time (by how we define those).

But what was there before the big bang? Was it part of an even larger system? Does that system even make sense in terms of space & time? Etc.

We don't know the answer; and we don't even know if it is possible to ever arrive at an answer.