Originally posted by Maslo
reply to post by ChaoticOrder
It very well may be curved and we just can't detect it, but if it isn't, then the theory that the Big Bang created space-time with it, is completely flawed.
Why, even an infinite universe can expand just as well as hyperspherical finite universe. Infinities come in different sizes. As an example, both integers and even numbers are infinite, but there is two times as much of integers than of even numbers. Just because we cannot imagine infinite expanding spacetime as simply as an expanding sphere does not mean that the idea is not mathematically consistent and valid.
Originally posted by ChaoticOrder
reply to post by fiftyfifty
No... infinity can expand. However infinity has no shape, it's infinite. It cannot be a sphere or anything else. The idea of a sphere which can contain infinite space is indeed mathematically invalid. Infinite flat space is just that - infinite flat space.edit on 2/10/2012 by ChaoticOrder because: (no reason given)
But the statement that infinity can expand simply does not hold.
Originally posted by magma
reply to post by fiftyfifty
Star
Infinite can not be flat
For it to be infinite it needs to have no boundry
For ever and ever
But the statement that infinity can expand simply does not hold. If something is expanding, it must have an observable end or edge or a volume.
Originally posted by CLPrime
Originally posted by ChaoticOrder
I would also like to know how the Universe can be expanding but also be infinite like they say.
Let's look at it this way...
Picture the series of Integers in the form of a line:
... -12 -11 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11 12 ...
...extending to infinity at either end.
As it stands, there is only a single space between each number. However, what happens if we add another space between each number? The distance between each number increases, but the infinite nature of the series stays the same.
This is the same as the expansion of the universe. Each of the universe's 3 spatial dimensions can be represented as an infinite series of numbers on, for example, a Cartesian grid. Each dimensional axis extends to infinity, but the distance between each point increases.
This is how universal expansion works, whether the universe is infinite or not.
Clearly you don't even know what 'flat space' means. Again, let me quote something from CLPrime:
I also disagree in what you call 'flat space'. if space was flat then there would have to be a top and a bottom.
Originally posted by CLPrime
Originally posted by ChaoticOrder
So it's like how large gravitational fields can bend space-time. You're saying that space-time is generally flat throughout the entire Universe unless disturbed by forces such as gravity? So would the spherical model perhaps represent some sort of Universe where space-time loops back around on it's self, or something like that?
Yep, all of those points are pretty spot on. The spherical universe is also the one where it's possible to see ourselves if we look out far enough... and, if we keep travelling in a "straight" line, we'll eventually come back to our starting point.
As Arbitrageur mentioned, it's still possible that the universe is curved like this. It just has to be such slight curvature that we can't detect it. That's why what scientists will usually say is that the universe is locally flat. The Earth is also locally flat to any given person standing on it.
This is the same as the expansion of the universe. Each of the universe's 3 spatial dimensions can be represented as an infinite series of numbers on, for example, a Cartesian grid. Each dimensional axis extends to infinity, but the distance between each point increases. This is how universal expansion works, whether the universe is infinite or not
As an example, both integers and even numbers are infinite, but there is two times as much of integers than of even numbers.
Well surely this points towards the universe not being infinite.
Originally posted by blobby
has no one measured which side of the edge of the universe is nearest to us? as we cant be slap in the middle, so one side has to be nearer to us than any other side?
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