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How do we know space is not infinite? 
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#37
Sep1211, 06:17 PM

PF Gold
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#38
Sep1211, 11:37 PM

P: 534

http://plus.maths.org/content/os/iss...topology/index http://www.csulb.edu/~scrass/Teachin...odecaSpace.pdf http://www.maths.lse.ac.uk/Personal/mark/topos.pdf 


#39
Sep1711, 07:59 PM

P: 78

my point is " some thing infinite can get bigger or smaller but it could have not been finite in the past, and will never become finite in the future " 


#40
Sep1711, 09:23 PM

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#41
Sep1911, 05:20 PM

P: 95

I see the Universe's "diameter" mentioned in two above posts.
I'm pretty sure the Observable Universe only has radius, and not diameter. To measure a diameter you need to be on the edge of the Universe (or any circle or sphere) and that's not possible in any version of the Universe. You can't simply multiply the radius by two and say it's diameter. 


#42
Sep1911, 05:35 PM

P: 95

I'll quote these two above posted arguments as very convincing:
 "how can you prove something like "infinite". It would take an infinite amount of time to measure something infinitely large." "The observable universe is finite. Given that is the only part observationally accessible, the rest is scientifically irrelevant until an observationally detectable effect on the observable part is confirmed."  The first argument can be given against anything being infinite, not just the Universe. 


#43
Sep1911, 07:23 PM

PF Gold
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#44
Sep2211, 04:44 PM

P: 38




#45
Sep2211, 04:49 PM

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#46
Sep2311, 12:55 PM

P: 728

Chronos by observable universe do you count the CMBR sphere or just the highest redshifted galaxies? The observable universe is shrinking all the time and eventually only our local group will be visible from our position. However isnt it pretty certain that the unobservable universe still exists both now and at that later time  unless we believe that the universe not homogenous and isotropic? 


#47
Sep2311, 01:14 PM

PF Gold
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What Chronos has said in other posts is that there basically ISN'T anything outside the OU because we can't TELL directly whether there is or not, but I think that's an overly restrictive point of view. I think the UNobservable universe exists now and will continue to exist but in practical terms, that doesn't seem to mean much since as Chronos always points out (correctly) we just can't detect it. It's not at all clear to me that there will EVER be any way to detect it, although I have heard, vaguely, that there are some theories that say there will be / may be observational evidence left over from the earliest times after the singularity that we WILL be able to observe remnants of. I don't get how this works but it would be neat if such things ARE ever observed. 


#48
Sep2311, 01:40 PM

P: 728

Perhaps I wasnt being clear. Try less of the matter in the universe will be observable in the future. However this wasnt the point I was trying to make.



#49
Sep2511, 05:22 AM

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#50
Sep2611, 08:01 AM

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#51
Sep2611, 11:28 AM

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#52
Sep2611, 12:06 PM

PF Gold
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#53
Sep2611, 12:34 PM

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#54
Sep2611, 03:36 PM

P: 728

Chris, I think I understand what you are suggesting. If the universe has an edge and we are relatively near it, then eventually we would see no more CMBR in that direction because it had all passed us by. I suppose we can keep looking!
I think that the observable universe is small compared to the whole universe because the CMBR is so flat in every direction implying homogeneity. However, if there was an edge of some kind I would not expect it to be a sudden transition either, there again we cannot discount any possibility, however remote, when we cannot make any observations. 


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