RE: I'm too dumb to be an atheist
March 8, 2014 at 11:16 am
(This post was last modified: March 8, 2014 at 1:52 pm by Tiberius.)
So I've been summoned into this thread via PM to comment on infinities. Whilst I don't claim to be an expert, I think Neil deGresse Tyson explains the concept quite nicely in this 1:25 minute video:
http://www.youtube.com/watch?v=nzQ4-gEesRg
Effectively:
The edge of the observable universe is simply the furthest point away from us (Earth) that light has been able to reach us from. This distance is about 13.7 billion light years away. Note that due to limitations on light speed (i.e. that the speed of light is not infinite) it is impossible to know whether there is any space beyond that edge, though it is quite likely that there is...we just can't see it.
The reason it's quite likely is that we already know there are galaxies that are moving away from us at speeds faster than the speed of light. If that sounds impossible ("nothing can move faster than the speed of light"), then you've hit upon the problem when talking about universal expansion compared to...well, any other kind of expansion.
I've seen analogies of universe expansion that liken it to a balloon gradually being filled with air. The material of the balloon remains the same mass, but the points that make up the balloon are all stretched and the distances between them become greater. Universal expansion is when space itself expands. That is to say, technically speaking, the galaxies themselves are pretty stationary (i.e. they don't move through space that much), but the space between galaxies is expanding. The problem with the balloon analogy is that the balloon is situated within space, and so it expands into other space. This is not true of the universe, because the universe is space. So in order to make the analogy correct, you have to imagine the balloon is the only thing that exists. It doesn't expand "into" anything, because it is the only thing that exists.
In this sense, the universe itself is infinite, the distances between certain points of space in the universe are being "stretched" at speeds which are getting faster the further apart the two points are (though the speed limit of objects within space itself remains a constant), and the observable universe (because it is limited by the speed of light) is expanding at the speed of light, and is most definitely finite.
That last paragraph can serve as a TL;DR btw. :-)
http://www.youtube.com/watch?v=nzQ4-gEesRg
Effectively:
The edge of the observable universe is simply the furthest point away from us (Earth) that light has been able to reach us from. This distance is about 13.7 billion light years away. Note that due to limitations on light speed (i.e. that the speed of light is not infinite) it is impossible to know whether there is any space beyond that edge, though it is quite likely that there is...we just can't see it.
The reason it's quite likely is that we already know there are galaxies that are moving away from us at speeds faster than the speed of light. If that sounds impossible ("nothing can move faster than the speed of light"), then you've hit upon the problem when talking about universal expansion compared to...well, any other kind of expansion.
I've seen analogies of universe expansion that liken it to a balloon gradually being filled with air. The material of the balloon remains the same mass, but the points that make up the balloon are all stretched and the distances between them become greater. Universal expansion is when space itself expands. That is to say, technically speaking, the galaxies themselves are pretty stationary (i.e. they don't move through space that much), but the space between galaxies is expanding. The problem with the balloon analogy is that the balloon is situated within space, and so it expands into other space. This is not true of the universe, because the universe is space. So in order to make the analogy correct, you have to imagine the balloon is the only thing that exists. It doesn't expand "into" anything, because it is the only thing that exists.
In this sense, the universe itself is infinite, the distances between certain points of space in the universe are being "stretched" at speeds which are getting faster the further apart the two points are (though the speed limit of objects within space itself remains a constant), and the observable universe (because it is limited by the speed of light) is expanding at the speed of light, and is most definitely finite.
That last paragraph can serve as a TL;DR btw. :-)
