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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Nothing prevailing outside of the current paradigm is immediately intelligibly, Just as the notion of a Higgs boson or event horizon or elsewhere outside of a light cone use to be.

I like the sound of it so far, even if I can't grok a good portion it. It is an abstract artform, at least.

No Higgs boson no mass. Could there be a massless starship? Such a ship might reach the speed of light, but as far as I know that is still a speed limit for just about anything.

E=mc^2 is the only thing that limits faster than light travel.

Even if you tried to make the argument that it is infinite because it is always expanding, that would still be finite. If you travel at a speed faster than its expansion, you would theoretically reach the end, right?

Hey Jason, greetings,
I understand your comment, but you've touched on my point: 
If you theoretically- or otherwise- reach the end, whats beyond the end? There has to be something past 'the end', doesn't there? Or else, how could you logically call it, 'the end'?
(just fun to think about)

Rick, you're right; it is fun to think about.

It's fun to not have a three-year-old ask "Why is it fun to think about?"

It's fun to shirk responsibility, which those who lead responsibility-shirking theists dare not do.

I would say, not if the only space that makes sense to talk about is the space between things. However, as we now know that space functions like a substance (being compressible and stretchable), it would all depend on how far out these properties extend. Do they go on and on indefinitely or are they something like a field created by the physical massive universe. Imagine the magnetic field around a magnet.

Let me rephrase a concept I failed to explain well enough previously.

No matter where one is or is going in the universe, it will seem like one is in the center of it, never getting closer to any kind of edge. Everywhere one looks will look the same: the farther one can see, the more red shift will be seen; until finally the red shift just looks like a fog of background radiation. You can see it, but you'll never actually "get there".

You could call this far off fog a "wall" if you like. But it's not a physical boundary. It's merely an artifact of what existed billions of years ago.

If the universe is infinite, it's easy to grasp why you'll never see a physical boundary, as it would just seem to go on forever an ever. But for ever and ever, who could ever prove or disprove it? No one.

If the universe is finite, it's harder to fathom that there is no "other side" to the fog. The fog is only a remnant of what once existed, and if one could actually, ever see all the way back to time 0, that would be "the beginning", not the end. You could never actually be there to see it, unless you could time travel.

Pope OoO:

No matter where one is or is going in the universe, it will seem like one is in the center of it,....

Yes. The book Big bang: A Critical Analysis makes and explains this point.

The spotted balloon metaphor makes the point visually. No matter which spot you occupy, as the balloon enlarges the other spots are all moving away from you.

The spotted balloon metaphor makes another point as well, it's not the spots that are physically moving, it's the rubber of the balloon that is expanding.

arch, the spots are moving farther apart?




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