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Supaiku
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I'm wondering if there's science that supports an infinite (in some way) universe
Danger said:Since we know when the universe began, and how fast it's expanding, we know that it has to be of finite size.
Sure, that's also possible. No one knows wheter the universe is infinite or not. (And it certainly does not care about "opinions" )The_Bled said:My opinion is that the universe is what is called in mathematics, a "three-dimensional torus". There are no edges, but it isn't infinite. Think of an ant on a beachball walking around on its surface. The universe is a three-dimensional flat surface that wraps around a four-dimensional sphere.
EL said:Sure, that's also possible. No one knows wheter the universe is infinite or not. (And it certainly does not care about "opinions" )
I notice the "wink", but may I ask why you choose to stick to just one option?The_Bled said:Well, since there are so many theories and nobody has ever flown to the edge of the universe, I think I'm stickin' to that.
EL said:I notice the "wink", but may I ask why you choose to stick to just one option?
SpaceTiger said:. . . we have a successful theory (inflation) that suggests that the present-day universe would look pretty much the same either way.
The_Bled said:I don't just stick to one option... that just seems to be like the most plausible theory to me. But... you don't know which one is right, so you talk about all of them... Whatever, back to the infinite universe topic.
saltydog said:Is this a cause for pause? Should not a "successful" theory account for only ONE possibility? I don't enjoy criticizing, esp. a field I love but to me, that's like saying the results suggest it's less than one and bigger than one at the same time.
mars2 said:I think it is a philosophic problem .And ...the universe is finite ,but it have no boundary.It seems like ...you walking on the ground but never fall over the cliff and leave our Earth ~~
^_^
Danger said:I believe you'll find that it's the other way around. Since we know when the universe began, and how fast it's expanding, we know that it has to be of finite size. It's generally thought to be unbounded, though, so you can go in the same direction forever without hitting the end.
How?ComputerGeek said:actually, I think it is infinite yet bounded.
EL said:Think of a 2D universe situated on the surface of a sphere. The area of this universe is finite, but anyway it has no boundaries where the 2D beings living there can "fall over a cliff".
Now you of course have to generalize this picture to a universe with 3 spatial dimensions, where the "area" is replaced by the "volume". Although our brains cannot really handle this generalization, this would give you a hint of how a universe could be finite and still unbounded.
Danger said:What I was getting at is that if it formed a finite time ago, and is expanding at finite speed, it can't be infinite.
mars2 said:Oh~~It is so involuted.:zzz:
You lost me on that one. How could it have been infinite when it formed? If it started at zero volume/infinite density, and is now at medium volume/medium density, then it had to have passed through small volume/high density on the way.EL said:If the universe was (spatially) infinite at Big Bang, which may have been the case,
Why not? Why must it have been finite?Danger said:How could it have been infinite when it formed?
Why must it have startet at zero volume?If it started at zero volume/infinite density
I fail to understand how the universe could have been spatially infinite at the beginning of time. For every cosmological model the volume contained within every boundary at the big bang is zero because for a zero scale factor a(t=0) = 0 the volume element is zero (or all distances are zero in the singularity). A different situation arises as soon as one considers any time slightly greater than zero, avoiding the singularity.EL said:The Universe started as a singularity of infinite density, but not necesary of zero volume.
hellfire said:I fail to understand how the universe could have been spatially infinite at the beginning of time. For every cosmological model the volume contained within every boundary at the big bang is zero because for a zero scale factor a(t=0) = 0 the volume element is zero (or all distances are zero in the singularity). A different situation arises as soon as one considers any time slightly greater than zero, avoiding the singularity.
Danger said:You lost me on that one. How could it have been infinite when it formed? If it started at zero volume/infinite density, and is now at medium volume/medium density, then it had to have passed through small volume/high density on the way.
SpaceTiger said:I think Ned Wright addresses this in a fairly straightforward manner:
http://www.astro.ucla.edu/~wright/infpoint.html"