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How do we know space is not infinite? 
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#1
Sep911, 02:33 AM

P: 38

How do we know space is not infinite? How can we be sure that the objects we see moving through space aren't just moving away from each other through space, rather than 'expanding space' as they change positions in outer space?



#2
Sep911, 06:31 AM

PF Gold
P: 6,506

We do NOT know for sure that space is or is not infinite but we DO know that space is expanding. If I understand it correctly, all galaxies are moving IN space in random directions but their motion relative to each other (small) is totally dominated (NOW) by their apparent motion (LARGE) due to the expansion of space. EDIT: if galaxies were NOT moving IN space in random directions, and in particular if they were all moving away from US (or from ANY single point) IN space, this would imply a pointposition for the big bang and I don't think you'll find any support in science for that point of view. FURTHER EDIT: Just in case you don't get another point, expanding space and infinite space are NOT in any way contradictory terms. 


#3
Sep911, 12:19 PM

P: 617

The observable universe is finite. The big bang happened about 14 billion years ago, so light from points in space that are 14 billionlight years away (actually 46 because of expansion) are just now reaching us and showing us the big bang. If we try to see farther than 46 billion light years away, we can't, because there is a wall of light caused by the big bang we are trying to see passed.
The unobservable universe may be infinite, but we can't know because we can't see it. But even if we could, how can you prove something like "infinite". It would take an infinite amount of time to measure something infinitely large. 


#4
Sep911, 01:00 PM

PF Gold
P: 6,506

How do we know space is not infinite?



#5
Sep911, 03:33 PM

P: 1

Just to be a bit more concise...yes, the Observable Universe is always finite, but also increasing every year.
At present the Comoving Distance has a radius of about 47 billion light years, while the diameter is, of course, doubled to around 93 billion light years. We can't actually see objects 93 billion light years away in one direction. 


#6
Sep1011, 12:19 AM

P: 186




#7
Sep1011, 01:07 AM

PF Gold
P: 6,506




#8
Sep1011, 01:18 AM

P: 56




#9
Sep1011, 01:50 AM

Sci Advisor
PF Gold
P: 9,488

Infinite is unbounded, so I fail to see your point.



#10
Sep1011, 03:55 AM

P: 1,666




#11
Sep1011, 05:14 AM

P: 534




#12
Sep1011, 05:15 AM

P: 534




#14
Sep1011, 11:59 AM

P: 191




#15
Sep1011, 12:04 PM

P: 534




#16
Sep1011, 03:33 PM

P: 191




#17
Sep1011, 04:20 PM

PF Gold
P: 6,506

infinity + 1 = infinity The thing represented by the word "infinity" is EXACTLY the same on both sides of the equation. If you can't get your head around this, then you will not get any further with the concept of infinity. This, by the way, is just an algebraic version of Hilbert's Hotel. 


#18
Sep1011, 05:15 PM

P: 191

My problem, not yours.,, 


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