Is the Universe Infinite or Finite? I was having that debate with a friend of mine today. My position was that it is finite because it is expanding. My logic was that the fact that is expanding indicates that it must be finite, because how could something be infinite and getting bigger?

His position was that it was infinite though he couldn't really explain why he thought that. (to give you some context, he also believes his daily horoscope offers him meaningful guidance and that aliens built the pyramids).

You may have guessed by now that neither one of us are physicists, so to settle the argument, I proposed that we contact an expert.

Confident of my correctness, I suggested to my buddy that we should have friend of this here site @seanmcarroll (the brilliant physicist and author of "From Eternity to Here") give us an answer.

I tweeted at Sean the subject line of this thread and he was kind enough to tweet me back in a matter of minutes. He said:

"Nobody knows. Sometimes that's the answer."

He then tweeted

"There may not even be an answer. de Sitter space (e.g.) can be finite or infinite depending on how you slice it."

So not wanting to badger Sean with follow up questions, I ask you: If we know the Universe is continually expanding (which to me suggests that it has a finite size that is increasing), how can it be labeled as anything other than finite?

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the universe only needs an edge if it is finite which leave you with the problem of what is beyond that edge for the universe to expand into. if it is infinite ofcourse it does not have an edge

Unseen:

infinity is a mathematical concept having no real world application.

By definition?

I was saying that it, like zero, exists only by definition.

I really enjoyed reading these post. I'm a biology major as of now and have always found the study of space fascinating. Thrilling to hear these types of opinions. 

Amazon has two books you will find of interest:

Big Bang: A Critical Analysis, by Eastman and others.

The Big Bang Never Happened, by Eric Lerner.

The first cites Einstein as having told LeMaitre at the 1927 Solvay conference, "Your physics is abominable."

In the above Tyson clip, he now has it both ways. This is not traditional Big Bang doctrine.

Science hasn't reached a point where it can answer this question. We don't have enough facts.

A millennia ago, we thought the universe revolved around the Earth. Just a century ago, we thought the Milky Way was everything. Then we learned that the universe contains countless galaxies, not just the Milky Way. Now it appears quite possible that our universe is one of many -- perhaps even one of trillions of universes.

If the universe began with a bang and has been expanding ever since, then the only way it could be considered infinite is in its geometry -- its shape. Not that I really understand it but the universe might have a saddle shape that would make it virtually infinite. Regardless, the notion of a universe that is infinite in size always seemed less than satisfying to me. One can easily imagine standing outside the universe and looking at other universes in the distance, twinkling like little stars.

There are different ideas of what a multiverse might be like. They might be like other dimensions coexisting with ours but to which we have no access of any kind. One theory suggests the weakness of gravity might be explained by the physics of such a multiverse. I think the notion of multiverse that's gaining the most favor right now is one in which space is unimaginably larger that we ever thought it was and is populated by many universes -- even an infinite number of universes -- moving away from each other so fast that they leave light in their dust and, thus, are not visible to each other.

It appears that, so far, the universe is only as infinite as our imagination.

Well I heard that if you go to the edge of the universe you come out on the opposite side

Our knowledge on the universe to answer this topic is simply minimal, therefore it is hard to say if it's finite or infinite.

I think until it's proven otherwise, we need to assume that the universe, while unimaginably large and complicated, is finite. If it is both physically real and infinite, it will be the first such thing. There are strange ways of talking about things in a mathematical way that produce an infinity of sorts, such as a mobius strip, a physical body with a two-dimensional surface but only one edge, such that, in a sense, it is an unbounded (or, better, uncontained) surface. But the key phrase there is "in a sense." As you make a mobius strip and look at it on your table, there is also clearly a sense in which infinitude does not apply.

I agree with you on that one, that is what most physicists are likely to believe for now. The universe is a physical structure and anything physical cannot be infinite, this is a contradiction in terms. The universe may give the illusion of infinity in the same way that the surface of a globe creates the notion of a infinite surface, however it is plain to see that the globe is a three-dimensional physical structure and has finite measurements.

"The universe is a physical structure and anything physical cannot be infinite, this is a contradiction in terms.

You're good. 

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