A universe can be finite without having boundaries. But as far as I know, present evidence recently points more to the "infinite" option.
I have no idea what a finite or infinite existence is supposed to mean.
Since both a finite or an infinite universe seems to be possible, it's hard to imagine how this question could be settled by any a priori argument.
I have no idea what a finite or infinite existence is supposed to mean.
Since both a finite or an infinite universe seems to be possible, it's hard to imagine how this question could be settled by any a priori argument.
You know, I think I'm finally beginning to understand spacetime.
I used to think that, if space was shaped like a sphere, then if we went straight we'd run into some kind of 'wall', which didn't make sense to me. What I didn't realise is that I'd be MOVING in a curved direction(To put it simply). However, if space was infinite, I'd just keep on going into nothingness.
Right?
I used to think that, if space was shaped like a sphere, then if we went straight we'd run into some kind of 'wall', which didn't make sense to me. What I didn't realise is that I'd be MOVING in a curved direction(To put it simply). However, if space was infinite, I'd just keep on going into nothingness.
Right?
Bikewer
Penultimate Amazing
I admit to being fascinated by cosmology, but also to being quite mystfied. I just chewed my way through "A Brief History of Time" (again...), and still find many of Hawking's concepts to be beyond me.
Even he says that the study is so specialized that only a tiny percentage of the population can claim to understand the current concepts in any meaningful way.
We have notions like "The universe if finite, but without boundary or edge." and the universe is a "sum over histories."
Regardless of the boundaries (or not?) of our own universe, there seems to be nothing to place a limit of only one, and the universe we live in may be one in an unimaginably-long series, or co-exist with essentially limitless others, outside our own space-time.
Though I have high hopes for the eventual resolution of these problems, I admit that infinity, with all it implies, is a difficult concept.
Even he says that the study is so specialized that only a tiny percentage of the population can claim to understand the current concepts in any meaningful way.
We have notions like "The universe if finite, but without boundary or edge." and the universe is a "sum over histories."
Regardless of the boundaries (or not?) of our own universe, there seems to be nothing to place a limit of only one, and the universe we live in may be one in an unimaginably-long series, or co-exist with essentially limitless others, outside our own space-time.
Though I have high hopes for the eventual resolution of these problems, I admit that infinity, with all it implies, is a difficult concept.
Re: Re: Re: Re: Infinite vs finite universe/existence
Let me explain it a bit more in detail.
Perhaps you have heard that the world is a fourdimensional 'spacetime'. Perhaps you have heard that new theories demand 11 dimensions. But for pedagogical reasons, imagine our universe having only two space dimensions (and one dimension for time).
Now what shapes could our universe have? It could be an infinite flat plane: infinite, euclidean, no boundaries.
It could be the surface of a ball (a sphere): finite, but still no boundaries: you can go round and round a sphere without finding any boundaries (remember, our universe and its inhabitants are only two-dimensional, so they can't dig the sphere or leave it into space).
Another possibility: the universe is the interiour of a circle, the circle the boundary of the universe. Such a universe would be finite and would have boundaries.
Another possibility: the universe is an inifnite flat plane with a hole in it. Such a universe would be infinite, but it would also have a boundary (the edge of the hole).
So you see, a two-dimensional universe can be infinite without boundaries, finite without boundaries, finite with boundaries, or infinite with boundaries.
You may imagine other possible shapes, like the surface of a torus, a projective plane, a hyperbolic plane, and so on.
Now the same holds if you imagine not a two-dimensional, but a three-dimensional universe. The universe could be an euclidean space (infinite, no boundary), the three-dimensional 'surface' of a four-dimensional hyperball (finite, no boundary), the interiour of a ball (finite, boundary) or an infinite space with holes (infinte, boundary).
Flatworm said:
Let me explain it a bit more in detail.
Perhaps you have heard that the world is a fourdimensional 'spacetime'. Perhaps you have heard that new theories demand 11 dimensions. But for pedagogical reasons, imagine our universe having only two space dimensions (and one dimension for time).
Now what shapes could our universe have? It could be an infinite flat plane: infinite, euclidean, no boundaries.
It could be the surface of a ball (a sphere): finite, but still no boundaries: you can go round and round a sphere without finding any boundaries (remember, our universe and its inhabitants are only two-dimensional, so they can't dig the sphere or leave it into space).
Another possibility: the universe is the interiour of a circle, the circle the boundary of the universe. Such a universe would be finite and would have boundaries.
Another possibility: the universe is an inifnite flat plane with a hole in it. Such a universe would be infinite, but it would also have a boundary (the edge of the hole).
So you see, a two-dimensional universe can be infinite without boundaries, finite without boundaries, finite with boundaries, or infinite with boundaries.
You may imagine other possible shapes, like the surface of a torus, a projective plane, a hyperbolic plane, and so on.
Now the same holds if you imagine not a two-dimensional, but a three-dimensional universe. The universe could be an euclidean space (infinite, no boundary), the three-dimensional 'surface' of a four-dimensional hyperball (finite, no boundary), the interiour of a ball (finite, boundary) or an infinite space with holes (infinte, boundary).
We have all heard that the stars and galaxies are 'fleeing' from us. Those which are the farthest from us are flying away from us at even a greater speed than those that are closer to us.
How do these scientists not know if instead of our universe expanding at some great rate, it is really all collapsing in towards some center somewhere. Couldn't this too explain the effect of stars moving away from us at great speeds where the closest ones move away...but the farther ones are even moving away at a faster speed?
Imagine that we are inSIDE a sphere (universe)which has stopped expanding, but is actually now collapsing inward. The stars closest to us AND closer to the center would be moving away from us, because gravity would be pulling the closer ones, faster. The stars just on the OTHER side of us, away from the center, would also APPEAR to be moving away from us, because due to relativity, OUR faster speed toward the center would make THOSE stars appear to be moving away from us.
Now take the stars that are farther from us yet. Those that are closer to the center of gravity (where the collapse is) would appear to be traveling away from us at a greater speed than the stars that are closest to us. Conversely, the stars way far away, that are both away from us and farther away from the center than us, would appear to be flying away from us at a greater speed also, because, in reality, it is US who is flying away from THEM faster, on the way towards the center.
Relativity being what it is...how do they not know that we are collapsing, instead of expanding?
How do these scientists not know if instead of our universe expanding at some great rate, it is really all collapsing in towards some center somewhere. Couldn't this too explain the effect of stars moving away from us at great speeds where the closest ones move away...but the farther ones are even moving away at a faster speed?
Imagine that we are inSIDE a sphere (universe)which has stopped expanding, but is actually now collapsing inward. The stars closest to us AND closer to the center would be moving away from us, because gravity would be pulling the closer ones, faster. The stars just on the OTHER side of us, away from the center, would also APPEAR to be moving away from us, because due to relativity, OUR faster speed toward the center would make THOSE stars appear to be moving away from us.
Now take the stars that are farther from us yet. Those that are closer to the center of gravity (where the collapse is) would appear to be traveling away from us at a greater speed than the stars that are closest to us. Conversely, the stars way far away, that are both away from us and farther away from the center than us, would appear to be flying away from us at a greater speed also, because, in reality, it is US who is flying away from THEM faster, on the way towards the center.
Relativity being what it is...how do they not know that we are collapsing, instead of expanding?
Ziggurat
Penultimate Amazing
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Iamme said:
That should cause an asymmetry, which we don't see. When we look outside our galaxy, as far as we can tell, the universe looks pretty much the same regardless of which direction you look. This leads to the basic assumption of cosmology, which is that the universe is basically isotropic. We cannot prove it, but it's the simplest scenario that fits with what we observe, and there's no reason to think otherwise. Given this assumption, that actually puts some major constraints on what kind of universe we could be living in.
I think you may misunderstand what people mean by the universe being a sphere: the idea is that three-dimensional space is in a sense wrapped around the surface of a four-dimension sphere, so that if you go far enough in any direction you'll always end up at the start. This is an isotropic universe. What you describe is not isotropic. Also, I think you somewhat misunderstand what the big bang is all about: it's not all the matter in the universe exploding (or collapsing) from a single point in some vast space, it's space ITSELF (along with all that matter) exploding from a single point. As the universe expands, it's not that galaxies move farther and farther away from each other, it's that the space itself between them gets larger and larger. Similarly, if an isotropic universe was collapsing, we wouldn't collapse towards a single point in space, but rather all of space would shrink, and everything would get closer to everything else.
Yes, but in such a scenario the stars to our sides would be pulling closer to us, so you'd be able to observe a major anisotropy around you - even if you couldn't tell which direction you were falling, you'd still be able to identify an axis. We do not observe any such anisotropy.
Because what you describe cannot occur in an isotropic universe, and we do not observe any large-scale anisotropies that would accompany your scenario.
Edited to fix formatting.