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Old November 23rd, 2012, 03:16 PM   #51
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Again, if the universe were indeed infinite, as by definition it couldn't be measured, by definition it would be impossible to know.
Easy as that.




That said, please be aware that the well attested & easily verifiable phenomenon of the expansion of the known universe is a bit different concept; such expansion is attestable for all the observable universe
Observable_universe Observable_universe
(by definition finite) which is not necessarily everything what exists (the usual definition of the word "universe")
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Old November 23rd, 2012, 05:49 PM   #52
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I'm just going to clarify this thread a little. First the question is very much still in debate in cosmology circles. There is no definitive answer one way or the other. One method that those that believe in a finite universe is to measure the curvature of space. Measuring the curvature of space we have found that the universe is no less then 750 billion light years across. Unfortunetly our measurements are not exact and inside the margin of error includes 0 and even negative numbers, although almost every cosmologist believes that space is not negatively curved. If curvature = 0, then space is infinite.

One point that was brought up was that if it was infinite now, it must have always been infinite. This is exactly true. That still doesn't prove anything though. Infinity can expand.

One final point someone said earlier that galaxies were moving away from us at close to the speed of light, actually the furthest galaxies are receeding at much faster then the speed of light. A related subject is called the hubble volume. These are galaxies far enough away from us the are moving away at speeds greater then the speed of light that light will never reach us.
Hubble_radius Hubble_radius

If the above is confusing, it should be. Just 1 thing to remember, objects cannot move faster then the speed of light, but space can expand faster then the speed of light.
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Old November 24th, 2012, 08:33 AM   #53
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Originally Posted by Telix View Post
I'm just going to clarify this thread a little. First the question is very much still in debate in cosmology circles. There is no definitive answer one way or the other. One method that those that believe in a finite universe is to measure the curvature of space. Measuring the curvature of space we have found that the universe is no less then 750 billion light years across. Unfortunetly our measurements are not exact and inside the margin of error includes 0 and even negative numbers, although almost every cosmologist believes that space is not negatively curved. If curvature = 0, then space is infinite.

One point that was brought up was that if it was infinite now, it must have always been infinite. This is exactly true. That still doesn't prove anything though. Infinity can expand.

One final point someone said earlier that galaxies were moving away from us at close to the speed of light, actually the furthest galaxies are receeding at much faster then the speed of light. A related subject is called the hubble volume. These are galaxies far enough away from us the are moving away at speeds greater then the speed of light that light will never reach us.
Hubble volume - Wikipedia, the free encyclopedia

If the above is confusing, it should be. Just 1 thing to remember, objects cannot move faster then the speed of light, but space can expand faster then the speed of light.
There are two ideas I just can't get my mind around. Infinity can expand? and space can expand faster then the speed of light? Infinity goes on forever. How can you expand beyond that? Space is empty. How can it bend or expand?
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Old November 24th, 2012, 08:58 AM   #54

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There are two ideas I just can't get my mind around. Infinity can expand? and space can expand faster then the speed of light? Infinity goes on forever. How can you expand beyond that? Space is empty. How can it bend or expand?

Ridiculous as it may seem, some infinities are bigger than others. I think the decimal infinity is larger than the regular number infinity. Then there's the infinity of fractions etc. The Horizon documentary a few pages back explains it.

The mathematician Cantor ended up in a mental institution, go figure.
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Old November 24th, 2012, 12:50 PM   #55

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Who says there is another side?

Space might be curved. Consider if we lived in a 2D world and it was a mobius strip.

Click the image to open in full size.

I believe the answer lies in this video:


Imagining 10 Dimensions - the Movie - YouTube


If anyone actually knows what the answer then they're a better wo/man than me.
do you mean curved in the sense of the shape of the universe. yet its been mathematically proven that the universe is flat which then supports the idea of a universe expanding without end.

the universe is infinite in the sense that it will go on expanding yet just before the big bang all matter was concentrated into a single almost palm sized ball. space and time expanded out from that yet for space to expand it needed to have a border to expand out from, even if its one that is always changing.
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Old November 24th, 2012, 01:39 PM   #56
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do you mean curved in the sense of the shape of the universe. yet its been mathematically proven that the universe is flat which then supports the idea of a universe expanding without end.

the universe is infinite in the sense that it will go on expanding yet just before the big bang all matter was concentrated into a single almost palm sized ball. space and time expanded out from that yet for space to expand it needed to have a border to expand out from, even if its one that is always changing.
No it has not been proven that the universe is flat. It has been proven that it is very close to flat.
Shape_of_the_Universe Shape_of_the_Universe

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The recent Wilkinson Microwave Anisotropy Probe (WMAP) measurements have led NASA to state, "We now know that the universe is flat with only a 0.5% margin of error."
0.5% margin of error means it could be positively curved, negatively curved or flat. Many physicists believe that the universe is positively curved, it may even be a majority, although I've never seen a poll on it. Unfortunetly when we measure curvature, you will always get a margin of error, meaning it may be actually impossible to prove a flat universe. At least with the current method, it is impossible through direct measurement.

Also the reference to the universe being in a palm sized ball is only a reference to the observable universe, that which is within 14B light years, while we know that the entire universe is much much bigger.

edit: I can see how the quote might be misleading. It makes it sound like they are saying that we are 99.5% sure that the universe if flat. That is not what they are saying. What they are trying to say is that the curvature of the universe is between -0.5% and 0.5%
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Old November 24th, 2012, 01:58 PM   #57
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There are two ideas I just can't get my mind around. Infinity can expand? and space can expand faster then the speed of light? Infinity goes on forever. How can you expand beyond that? Space is empty. How can it bend or expand?
I think EoR covered infinity fairly well so I will jump to your questions regarding space. I've never really heard a good intuitive way of understanding how space can bend, only that the evidence shows that it clearly does. In fact, it is one of the fundamental principles of relativity. Everything in space travels in straight lines, we have orbits because the objects in space are bending space. Sort of like a race car turning on a very sharp bank, they barely have to turn the wheel at all to stay on track. In fact, a black hole is an area where gravity is so strong and concentrated in such a small space that space is bent entirely in on itself, with all directions leading towards the center of the black hole.

As far as how can space expand, this is another tough one to answer, this will probably sound like I'm avoiding the answer, but well... in physics space isn't really treated as a physical entity. It is more just mathematics, when they say that space is expanding, what they really mean is that the angles are changing. I know that doesn't really make a lot of sense, but if it makes you feel any better, the math works great!
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Old November 24th, 2012, 02:09 PM   #58

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I have the same perception that the rules of physics as it is known to the people may not apply in the whole of the universe because of its relativity but, indeed mathematics can do the trick.
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Old November 24th, 2012, 02:24 PM   #59

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Originally Posted by Telix View Post
No it has not been proven that the universe is flat. It has been proven that it is very close to flat.
Shape of the Universe - Wikipedia, the free encyclopedia



0.5% margin of error means it could be positively curved, negatively curved or flat. Many physicists believe that the universe is positively curved, it may even be a majority, although I've never seen a poll on it. Unfortunetly when we measure curvature, you will always get a margin of error, meaning it may be actually impossible to prove a flat universe. At least with the current method, it is impossible through direct measurement.

Also the reference to the universe being in a palm sized ball is only a reference to the observable universe, that which is within 14B light years, while we know that the entire universe is much much bigger.

edit: I can see how the quote might be misleading. It makes it sound like they are saying that we are 99.5% sure that the universe if flat. That is not what they are saying. What they are trying to say is that the curvature of the universe is between -0.5% and 0.5%
thanks for clearing up that bit on a flat universe

as for the bit on the palm sized universe i was referring to right before the big bang when all matter was packed in tightly before expanding out. its mentioned some bit here from about 15:10
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Old November 25th, 2012, 10:41 AM   #60

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Could one have an infinite amount of matter coming into being at the big bang, which would then expand to form an infinite universe? Surely it doesn't make sense to think of anything infinite expanding from a more restricted space.
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