Quizzes & Puzzles1 min ago
The Expanding Universe
38 Answers
Ok. This is the thread suggested in the Alien Astronauts thread. I'm not asking so much for what the expansion is (I'm willing to accept for now the idea that space growing/being created is the main driver, and actual motion of "stuff" is a lesser effect and occurs within the existing universe) I'm more into trying to get to understand of the idea that the universe isn't really growing after all, that it's all just measurements, and may have always been infinite.
So what is this idea that the universe started from a small area (maybe singularity) if everything to do with expansion is merely to do with spatial measurement on the largest measurable scales of our universe ?
Either,
a) ~14 billion years ago, the universe really was small, hardly any space/volume, in which case there has been a real expansion, rather than just a measurement thing, (regardless how that occurs - space being created is fine, although the cause would be a nice thing to know (but wiki adventures lead to "false vacuums" and "instantons" (!)¹)). In which case the issue regarding how a finite volume can become finite in the elapsed time since, is still an unexplained issue.
Or,
b) the universe was always infinite, which then leads us to two more options.
i) Either we have an infinite universe that started out extremely (infinitely ?) hot and dense throughout it's infinite size
ii) Or the "Big Bang" was some kind of local event within an infinite universe.
(I'm assuming ii is fairly unlikely).
Am I meant to accept an infinite universe, all of which is in an explosive state, bereft of even quarks etc. which sorted itself out throughout afterwards ? An infinite universe coming into existence seems a little far fetched.
¹ Sometimes I think it'd be nice to sit in on the early first year or whatever university physics lectures. They ought to have a public gallery ;-)
So what is this idea that the universe started from a small area (maybe singularity) if everything to do with expansion is merely to do with spatial measurement on the largest measurable scales of our universe ?
Either,
a) ~14 billion years ago, the universe really was small, hardly any space/volume, in which case there has been a real expansion, rather than just a measurement thing, (regardless how that occurs - space being created is fine, although the cause would be a nice thing to know (but wiki adventures lead to "false vacuums" and "instantons" (!)¹)). In which case the issue regarding how a finite volume can become finite in the elapsed time since, is still an unexplained issue.
Or,
b) the universe was always infinite, which then leads us to two more options.
i) Either we have an infinite universe that started out extremely (infinitely ?) hot and dense throughout it's infinite size
ii) Or the "Big Bang" was some kind of local event within an infinite universe.
(I'm assuming ii is fairly unlikely).
Am I meant to accept an infinite universe, all of which is in an explosive state, bereft of even quarks etc. which sorted itself out throughout afterwards ? An infinite universe coming into existence seems a little far fetched.
¹ Sometimes I think it'd be nice to sit in on the early first year or whatever university physics lectures. They ought to have a public gallery ;-)
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I didn't even notice. The brain is cool like that.
Anyway, (iib) is certainly wrong, as you said -- the Big Bang happened everywhere in the Universe at once, and that's true whether or not it's infinite.
We don't technically know which, by the way. There's no measurement I know of that can prove the Universe is infinite, as opposed to simply bigger than we can ever see -- although of course that won't stop physicists from trying. (The Cosmic Microwave Background helps, a bit, to show that at least the Universe is larger than the Observable Universe, but that might be as far as we can go).
I think the Universe being finite is actually weirder. If it were finite then either you could travel in any direction and eventually hit a literal wall, or (more likely) you would do the sort of Asteroids thing, and eventually (in particular, in a finite time) arrive back at where you started. That happens if the Universe is similar to Earth, or to a doughnut, or something of that kind.
But a Universe that's finite, but also expanding, opens up the real possibility that it's expanding into something. It would have, in some dimension, a finite size, so that you could potentially imagine extending that dimension to beyond the bounds of our Universe and into... well, something. I don't know what. But it might have "room" for other Universes, also finite, and that opens up a whole can of worms and I don't want to go any further in that direction for now, as it's very speculative and anyway not really what the question is about.
So let's go with an infinite universe, and see if that makes more sense.
(TBC)
Anyway, (iib) is certainly wrong, as you said -- the Big Bang happened everywhere in the Universe at once, and that's true whether or not it's infinite.
We don't technically know which, by the way. There's no measurement I know of that can prove the Universe is infinite, as opposed to simply bigger than we can ever see -- although of course that won't stop physicists from trying. (The Cosmic Microwave Background helps, a bit, to show that at least the Universe is larger than the Observable Universe, but that might be as far as we can go).
I think the Universe being finite is actually weirder. If it were finite then either you could travel in any direction and eventually hit a literal wall, or (more likely) you would do the sort of Asteroids thing, and eventually (in particular, in a finite time) arrive back at where you started. That happens if the Universe is similar to Earth, or to a doughnut, or something of that kind.
But a Universe that's finite, but also expanding, opens up the real possibility that it's expanding into something. It would have, in some dimension, a finite size, so that you could potentially imagine extending that dimension to beyond the bounds of our Universe and into... well, something. I don't know what. But it might have "room" for other Universes, also finite, and that opens up a whole can of worms and I don't want to go any further in that direction for now, as it's very speculative and anyway not really what the question is about.
So let's go with an infinite universe, and see if that makes more sense.
(TBC)
" Surely it would be expanding into nothing. It would be creating a something as it goes."
Yes, that can also be true. I suppose I mean that it's more plausible to imagine other "universes" existing if the one we have is itself finite. Like planets in space, there might be Universes in another space.
It's not necessary, but it is perhaps more plausible with a finite universe to imagine something beyond it.
Yes, that can also be true. I suppose I mean that it's more plausible to imagine other "universes" existing if the one we have is itself finite. Like planets in space, there might be Universes in another space.
It's not necessary, but it is perhaps more plausible with a finite universe to imagine something beyond it.
I wonder if it is creating its own nothing to expand into as it expands?....so, reading from out to in you'd have an undefined state of undefined shape and possibly infinite size, then within that, a "skin" of "real" nothing that is the same shape as the universe, but very slightly bigger and is continually destroyed as the universe expands into it and continually recreated to provide something for the universe to expand into, and then in the centre the actual expanding universe itself.
Ok: but how would that help ? Surely there already is nothing by definition because there's no something to grow into; so no obvious need to create a further layer of nothing to create something in from the nothing there.
I think we're in peril of assuming we need to create one state from the other in some kind of circular neverending process. The universe needs to grow by creating something so it creates nothing first, but this will need to be created in turn from something, which it'll have to create from some nothing, which in turn it'll need to create from something, which is made from some nothing...
I think we're in peril of assuming we need to create one state from the other in some kind of circular neverending process. The universe needs to grow by creating something so it creates nothing first, but this will need to be created in turn from something, which it'll have to create from some nothing, which in turn it'll need to create from something, which is made from some nothing...
My instinct is that it's probably "solving" a problem that isn't really a problem and creating a new one alongside. I did think about it for a while without making much progress.
But this is one of the other small problems, I'd suggest, about a finite universe conceptually. I was hoping to discuss an infinite one later -- may take a while longer, sadly.
But this is one of the other small problems, I'd suggest, about a finite universe conceptually. I was hoping to discuss an infinite one later -- may take a while longer, sadly.
