Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: paul.fr on 18/05/2007 19:46:28
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erm...Where is the "edge" of the Universe?
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OH MY GOSH!!!! i have always wondered this. everyone says it's never ending but that just doesn't seem possible!! this question usually keeps me busy for days... i can't figure it out! hopefully someone else can!
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What do you mean by 'the edge of the universe'?
The universe is about 13 billion years old, thus by definition, we cannot see anything that is more than 13 billion light years away (because light simply would never had time to reach us from further away, and since nothing can travel faster than light, so nothing else from further away could possibly have yet reached us).
So, for all practical purposes, the universe has an edge that is about 13 billion light years away (but constantly getting further away as the universe gets older). What is beyond that, we simply cannot know, because nothing from further away can reach us to tell us what is there.
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So, there is an edge. But that edge is not static! it just keeps expanding?
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is something else getting smaller as the universe expands?
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So, there is an edge. But that edge is not static! it just keeps expanding?
There is, for practical purposes an edge, insofar as a point beyond which we cannot see; but ofcourse, it is not an edge in the sense that with most things we think of an edge between one known thing and another known thing, but as edge between the knowable and the unknowable.
And, yes, it does keep expanding.
Ofcourse, if the universe ever goes from being a Big Bang, to a Big Crunch, and thus if at some time in the future the matter within the universe stops expanding, and starts to compact; this boundary between the knowable and the unknowable will still continue to expand, and so matter would start to be comming back through that boundary.
I am tempted to say that this fact alone would seem to make it unlikely that there ever will be a Big Crunch.
It must also be said that the edge of the universe is not absolute but relative - i.e. the edge of our Universe is about 13 billion light years away from us; but for someone living on a planet 3 billion light years away from us, he too will see an edge to his Universe that is 13 billion light years away from him, but his sphere of 13 billion light years will be centred on him, while our 13 billion year sphere will have a centre that is 3 billion light years away from his sphere, because it will be centred on us.
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is something else getting smaller as the universe expands?
Not that we are aware of (or at least nothing that I am aware of).
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There is, for practical purposes an edge, insofar as a point beyond which we cannot see; but ofcourse, it is not an edge in the sense that with most things we think of an edge between one known thing and another known thing, but as edge between the knowable and the unknowable.
And, yes, it does keep expanding.
Assume we are at the centre of the universe, and have our compass points. Is the universe expanding more in a north - south directon, east - west or at all points?
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If we are talking about expansion of the universe with regard to the expansion of the event horizon of the universe (rather than the Hubble expansion), then inherently we must always be at the centre of our own event horizon, and that event horizon must always be expanding equally in all directions. Fir the event horizon to expand faster in one direction than another would require that the speed of light be different in one direction than another.
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Ok. if the universe is expanding in all directions, what "space" is it occupying! Is it taking over an area, part of space that was not within our universe? or, as it expands is it creating new "space", or something else?
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Ok. if the universe is expanding in all directions, what "space" is it occupying! Is it taking over an area, part of space that was not within our universe? or, as it expands is it creating new "space", or something else?
Since, as I mentioned above, what is beyond our event horizon is unknowable, so we cannot know what space it occupies.
My undersatanding is (and maybe someone will correct me) that the Hubble expansion is actually faster than the expansion of the event horizon, so there is no risk (so long as that situation remains) of new matter entering our universe through the expanding event horizon (on the contrary, if I recollect correctly, we are actually losing matter through that event horizon).
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Do you think that there is an end to Space?
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There is another topic that deals with this question, but I can't remember what it was called!!
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There is another topic that deals with this question, but I can't remember what it was called!!
Not many topics deal with the event horizon, although quite a few deal with the Hubble expansion.
Dealing with the event horizon, we have :
http://www.thenakedscientists.com/forum/index.php?topic=3113.msg24498#msg24498
http://www.thenakedscientists.com/forum/index.php?topic=6676.msg70798#msg70798
(incidentally, in both threads, Ian (SoulSurfer) speculates on the possibility of a universe that does not completely fill our event horizon).
Dealing with Hubble Expansion, we have:
http://www.thenakedscientists.com/forum/index.php?topic=4298.0
http://www.thenakedscientists.com/forum/index.php?topic=6149.0
http://www.thenakedscientists.com/forum/index.php?topic=7675.0
http://www.thenakedscientists.com/forum/index.php?topic=3598.0
http://www.thenakedscientists.com/forum/index.php?topic=2366.0
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Let us make some reasonable assumptions.
Our place is much the same as any other.
What I see looking out in one direction looks much the same as in any other on a 'large scale'.
That's isotropy and homogeneity.
It means the universe we know should not change just because we 'lose sight' of the rest of it. The other way is more or less 'magic', because then everything we 'know' to be true is just a local fact, including the mathematics and physics we use for your laptop.
Let us now 'probe' the outer reaches of what we can see. It's about 13 billion light years away, because before that no light have reached us. That 'age' is also the age of the first 'light' existing in this universe. Before that we can't see anything.
Now move yourself to that 'edge' of a 'first light'.
Would you expect the universe to vanish there? And what would you expect to see looking back at the sun you 'just left'. The 'first light' right? Because that will still be as far as you can see from your new 'SpaceTime position'.
But what about that other 'side' of the universe that's 'new' to you.
You think it ends there?
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Really nice.
" "Life is not measured by the number of Breaths we take, but by the moments that take our breath away." "
And true Karen
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Here's one man's answer to the OP.
http://wtamu.edu/~cbaird/sq/2016/01/20/where-is-the-edge-of-the-universe/
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The event horizon of a black hole at one end and the atom on the other
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You will need to keep pushing the envelope infinitely to reach the edge.
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And that's scientific too.
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The event horizon of a black hole at one end and the atom on the other
What is that supposed to mean, exactly?
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Many scientific publications mention an "edge of the Universe".
Example:
Once you create a neutrino, a tiny subatomic particle, it moves at the speed of light, and it doesn't stop. It keeps going in a straight line to the edge of the universe. Straight through any stars, planets, or mountains; straight through any atoms, nuclei, or other particles that happen to lie in its path.
https://www.discovermagazine.com/the-sciences/the-unbearably-unstoppable-neutrino
The "edge of the Universe" is simply a reference to the boundary of one's perspective on his/her environment which could have been the "edge of the Earth" when people did not know yet that the Earth was round, and today it could refer to the edge of what is known about space.
By looking further, one's perspective can change. From "the edge of the Earth" to "the edge of the Universe" to "the edge of human knowledge about its environment".
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erm...Where is the "edge" of the Universe?
There is no edge to the universe. An often used analogy is a sphere whose surface the inhabitants reside in. No matter where on the surface you go you're still in the universe. The thing with this universe is that if the inhabitants take a walk in the straightest line possible they will come right back to where they came from. This is called a closed surface whose curvature is possible. Another surface is a flat plain. It's curvature is zero. Walk in a straight line and you'll never come back to where you started from. The flat universe is infinite in size.
Our universe appears to be very close, if not exactly, to being flat.
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Beautifully expressed Pete.
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This aligns perfectly with that conclusion of yours. It also say no to the Big Rip or the Big Crunch.
https://www.forbes.com/sites/startswithabang/2018/07/19/how-the-planck-satellite-changed-our-view-of-the-universe/
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There is no edge to the universe.
Physics, maths and, possibly, intuition tell us that this is probably so, but as far as I’m aware, there is no observational evidence.
An often used analogy is a sphere whose surface the inhabitants reside in. No matter where on the surface you go you're still in the universe.
Excellent analogy for a, very distinctly, curved (closed) universe.
Another surface is a flat plain. It's curvature is zero.
Could this let in the possibility of a boundary? It seems not, because…..
The flat universe is infinite in size.
Could this be paraphrased as: “the universe is flat, therefore it is infinite? Does one necessarily follow from the other?
Our universe appears to be very close, if not exactly, to being flat.
So, all options are open. I like that.
Please, Pete, don't think I'm questioning your superior knowledge, here. Hopefully, you know me well enough to appreciate that I have to try to get my own thoughts straight.
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It's curvature is zero.
How do you interpret non-zero curvature?
Our universe appears to be very close, if not exactly, to being flat.
I'll say that within some measurement uncertainty, observable universe is flat.