Is the universe infinite?

[Whateverist]

It may or may not be infinite but no one has found the edge of it yet.

If it loops in on itself it can be finite and you would never find the edge.

Drat, foiled again. Well played, God. Well played.

[vorlon13]

With the 'edge' of the observable universe receding from us at near lightspeed, our hopes of (our descendants) ever reaching it are nil, and even if it was reachable, it turns out the view from there is equivalent to the view from here.

For hypothetical beings there (at the distant edge of our observable universe) looking our way, we are at the 'edge' of their observable universe, but we can cast our gaze further along their same sight line towards us, and note we see at the 'edge' of our observable universe what they see at the 'edge' of theirs. And you can keep doing this thought experiment further and further in that direction and never get to a region of the universe that is lopsided looking, implying an actual 'edge'.

So we have an infinite universe of finite age. Weird, huh ?

[Anomalocaris]

With the 'edge' of the observable universe receding from us at near lightspeed, our hopes of (our descendants) ever reaching it are nil, and even if it was reachable, it turns out the view from there is equivalent to the view from here.

For hypothetical beings there (at the distant edge of our observable universe) looking our way, we are at the 'edge' of their observable universe, but we can cast our gaze further along their same sight line towards us, and note we see at the 'edge' of our observable universe what they see at the 'edge' of theirs. And you can keep doing this thought experiment further and further in that direction and never get to a region of the universe that is lopsided looking, implying an actual 'edge'.

So we have an infinite universe of finite age. Weird, huh ?

The assumption that the universe is more or less homogenous on a much larger scale than what we've observed, ie another observer at the edge of any particular observable universe will always see much the same thing as an observer in the middle, does not seem to be anything more than an assumption. It seems to me we don't have anything like an ability to form a comprehensive and accurate description of what can come out of the Big Bang, much less predict whether what came out of the Big Bang is really all there is.

I think it is fair to say we don't know if the universe beyond our visibility horizon is really uniform, similar to the part visible to us, and extends forever, or if it is nonhomogenous, and would become drastically different from the parts visible to us, including perhaps coming to an edge, or loop back to where we started, if we were able to go far enough.

[vorlon13]

We know for sure to 3X from my simplistic geometrical angle and the WMAP results I think gets you way beyond that.

And if you're willing to wait a few googleplex years, even that 3X distance gets kinda staggering.

[Anomalocaris]

We know for sure to 3X from my simplistic geometrical angle and the WMAP results I think gets you way beyond that.

And if you're willing to wait a few googleplex years, even that 3X distance gets kinda staggering.

Way beyond what? Accelerating expansion of the universe means almost everything will eventually recede from us at accelerating rate. Expansion of the universe is not limited by light speed, so almost everything will eventually surpass light speed as they recede from us. The size of visible universe, on the other hand, grows at fixed rate equal to speed of light. So time will not allow us to see more of the universe. It will restrict us to seeing less and less of the universe as time goes on.
In a googleplex years, the visibility horizon might be a googleplex light years. But by that time a googleplex light years might barely be big enough to contain a single proton, everything else having been carried beyond the confines of a sphere a googleplex light years in radius by expansion of universe.

[robvalue]

It's possible that it has no boundaries, but is not infinite. What appears to be 3D space could in fact be the surface of a 4D object. If so, you'd eventually "wrap around" like if you travel on the surface of a sphere. Or like pacman.

EDIT: whoops, seems this has already been mentioned.

[Anomalocaris]

It seems to me there are only three possible ways to become persuaded that we know whether the universe is infinite (in the sense it is basically similar everywhere and goes on forever without coming back to the same point) or not (space with properties that would make us call it part of the universe only goes out so far before coming to an end or coming back to the same point):

1. We perfect such a powerfully, precisely, accurately and fundamentally predictive model of the physics of the Big Bang that we have some considerable confidence in what it predicts for region of space beyond our visibility horizon.

2. We discover some form and information transfer that is faster than speed of light with which we can probe for properties of what lies well beyond current visibility horizon.

3. The thing that lies closer to the origin of the Big Bang than inflation - call it primordial atom - contained information that can be used to predict the outcome of the Big Bang, inflation and expansion, and the subsequent process of inflation and expansion nonetheless left enough residual information from the primordial atoml intact within in our visible universe for us to use to reconstruct what inflation and subsequent expansion of the universe has pushed beyond our direct observational horizon. ie, universe beyond our visibility horizon may have left evidence of its impact upon our part of the universe before the inflation, and from the nature of the surviving evidence of these impact we can deduce what nature of the universe beyond our visible horizon would have been.

[robvalue]

I read somewhere about testing whether the universe is a simulation by seeing if the laws of physics start to go wrong at the boundaries (if there are some). But I don't get that, because how could we know that a real universe doesn't just go wobbly near the boundary anyway? The laws of physics are just our observations after all.

Simulation hypothesis. Mindfuck. I'm cool with it, though. This business of having a maximum speed, even maximum relative speed, seems to me to imply some sort of #BUFFER FULL limitation in a program. Maybe.

[Whateverist]

It seems to me there are only three possible ways to become persuaded that we know whether the universe is infinite..

Oh where's the fun in that? Here are three ingredients sure to produce some pretty impressive predictions:

1) Imagination

2) Metaphors

3) Confirmation bias

The possibilities are limitless. Don't listen to the nay sayers, boys and girls. Get out there and have some fun creating your very own cosmos! And remember, you're never limited to figuring things out so long as you retain the capacity to make shit up.