Space can’t go on forever can it?
But what could stop it and what would be on the other side of that barrier?
Huh?!?!?
Why not?
On the other hand, consider the surface of the Earth (or any spherical object). It’s not infinite in size, but it doesn’t have any sort of “edge” or “boundary” - it’s a continuous closed surface. You can travel an unlimited distance in a straight line on the Earth’s surface without leaving it. The Universe could be like this, but in three dimensions rather than two - however, I believe that the latest astronomical observations say that it isn’t. Don’t know the precise details, I’m afraid.
At the moment there’s a bit of a debate about this, amongst astrophysicists. From the point of view of elegance, most seem to want to find enough mass in the known universe to counter-act the expansive forces imparted by the Big Bang. However, what we can see isn’t enough to cause everything to slow down, and collapse.
So, some go looking for ‘dark matter’ - any kind of matter that’s hard for astronomers to actually observe directly.
Others seem to say, okay - we’re stuck with an open universe, and it’s going to just keep expanding and expanding and expanding.
As for what’s on the other side of the boundary? I’ve not the foggiest - I think it’s a Schroedinger’s Cat thing - you can’t know. I do know that the math involved with so-called Black Holes and other superdense objects and matter gets really weird. And based on that, some really outre theories have been proposed.
My favourite theory (for which I offer no evidence, nor even any vaguely “scientific” arguments, since like OtakuLoki I believe it’s largely a matter of personal belief) is that our universe is finite and exists in a larger space, full of similar other universes. This larger space is itself contained in a larger space, and so on ad infinitum. Of course, this also applies “downwards” as well - we will eventually discover that there are smaller bits of matter that form quarks, etc… That’s called the infinite divisibility of matter, and I see no reason why it shouldn’t extend “upwards”, too. I think there are arguments against this, but that’s probably GD territory.
I had a trig teacher in school who said that the only thing harder to imagine than an infinite universe is a finite one. He also said that parallel universes were easy to imagine because they figure so much in pulp science fiction.
Let me throw the question back:
How could the universe NOT be infinite?
I mean, do you come to a wall or a door or a moat? And if you do, something has to be on the other side of it.
Think about a few hundred years ago when people looked out at the ocean and thought if you sailed far enough out, you would fall off the earth - that was their realm of thought. Ridiculous now, but real enough back then.
Perhaps in 500 or 1000 years they will laugh at us idiots who never understood the simple matter of travelling through worm holes and going 100 billion miles to the planet Czendion for a weekend vacation.
And OMG, it’s full of turtles! :eek: 
Sorry. 100 billion miles leaves you a long way beyond Pluto, but a bare 0.04% of the way to Alpha Centauri.
Kind of a hijack but could someone answer this question?
Some friend and I were talking about the big bang and I know I’ve heard this before, the thing about if the big bang happened all the galaxies or bodies in space would spin in the same direction, yet some spin in the opposite, thus the big bang theory is incorrect. Is this accurate or is their some reasonable explanation that does not disprove the big bang theory.
Umm… I think the burden of proof is still on you there… “if the big bang happened all the galaxies or bodies in space would spin in the same direction,” – why should that be so??
The big bang happened with space, time, matter, and energy expanding out of a superatom singularity, or something like that. The big bang would not have had ‘spin’ of its own. Within the first few instants, irregularity in the distribution of matter, and the force of gravity, would probably have created turbulence eddies, starting local clumps of matter to spin this way and that, however I don’t think this process would have given all matter the same ‘spin.’ Thus, it seems quite intuitively logical to me that the big bang could lead to some bodies in space spinning in one direction, some spinning in the other.
Anyone have a counterpoint??
Well the friend, not me is the one who made the argument that the big bang theory is false because of this, and I am pretty sure that his argument is incorrect I just didn’t have the facts to back me up at the moment.
Okay, this is off the top of my head, and very loose.
The problem with predicting that all of the matter in the universe would spin in the same direction because of the big bang it makes a couple of unwarranted assumptions:
First, for the initial microsecond, or less, after the Big Bang there was no matter. So making assumptions based upon the behavior of matter in other explosions is not a valid assumption. I don’t have the exact numbers here, but one of the reasons that a number of physicists are so excited by newer and larger cyclotrons is because it allows us to observe energy states closer and closer to what existed immediately after the Big Bang.
Secondly, and more importantly, the expansion after the Big Bang is provably not uniform. This is a bit harder to explain, so bear with me a minute, please. There is a phenomenon in high energy physics where a particle moving fast enough will bleed off energy by a process called pair production: A fraction of the particle’s energy, in the presence of a large mass (on the nuclear level, here) will be converted to a positron and an electron. The produced pair then, usually goes into mutual attraction, and annihilate each other - producing gamma radiation. The important thing to see, here, is that converting energy to matter is always going to produce matter/anti-matter pairs. It’s inherent to current understanding of nature, at least.
So - why does this mean that the Big Bang wasn’t uniform?
Well, basically, it comes down to the following evidence: We exist.
Normally, as I said, when energy is converted to matter it results in immediate matter/anti-matter annihilation. So, if the Big Bang had been of uniform density and composition, it would seem that the majority of matter created as the universe expanded and cooled down would have simply converted back to energy. Therefore, it’s been decided that the Big Bang was “lumpy.” That is, it wasn’t uniform.
Among other effects of this lack of uniformity - whorls, and other chaotic flows can be assumed to have happened. Which would randomize rotations. Among other things. If your friend wants a real problem with the Big Bang, tell him about the matter/anti-matter thing. Even assuming lumpiness in the Big Bang, we’re still stuck with evidence of our eyes that seems to contradict all we know about matter being created from energy.
Who’s to say it hasn’t already collided on the other side, and now we’re just waiting for the ripple back effect. :eek:
That’ll mess things up.
I’m pretty sure that dark matter was predicted in order to explain why the edges of galaxies spin as fast as the middle. Like, in our solar system, the further out planets are, the slower they orbit (because of the reduced pull of the sun’s gravity).
In galaxies, however, the outer edges ‘orbit’ the center of the galaxy just as fast as the middle.
One explanation would be a lot more ‘unseen’ matter that was balancing the gravitational effect everywhere.
I don’t think it has anything to do with ‘wanting’ the universe to contract again.
Okay, let’s clear the slate here and start by redefining some terms. Well, one term.
The Universe: The Universe is everything that exists. Anywhere. Ever.
That said, it’s clear that the Universe cannot have some finite boundary within its own dimensions. Maybe by some fluke there is some kind of shell of matter or whatever at a large radius from the Milky Way, but there will be the entire remainder of the Universe beyond that shell. Even if the remainder of the Universe is that shell.
In other words, you have to be able to travel an infinite distance in a straight line without ever leaving the Universe, and without coming up against something that is not the Universe (there is nothing that is not in the Universe). Whether you get back to where you started in doing so is another question entirely. If that were the case, the Universe would be toroidal in shape - the Cosmic Donut, if you will. The evidence against this (which has by no means ruled it out entirely) comes from probes that measure the background radiation to better than one part in a thousand. Doing so provides an image of the Universe about 300,000 years after the big bang (right when the plasma condensed to electron-proton atoms and allowed light to propagate without banging into stuff), and the best images we have now suggest that overall spacetime does not possess the necessary curvature to be toroidal - rather, it is (in general) flat. However, this is a tentative conclusion, awaiting confirmation (or disproval) by future results.
As far as this “spin” business goes, there are two possible ways I can interpret that term. One is the spin that subatomic particles like electrons and protons and photons, etc., are said to have. These are clearly not all in the same direction. In fact, in order to have a stable, neutral multielectron atom you need electrons of opposite spin in each orbital. So whatever processes governed the Universe up to the creation of the first stars obviously made electrons (and thus, presumably, all particles) of different spins, otherwise no helium or heavier elements from fusion. But here’s the kicker: a particle’s spin isn’t constant or immutable in any way. The entire basis of quantum computing is that they change the atoms’ spin with radio waves, which means that even if the big bang DID make electrons of, say, all spin up, some of them could have been changed by interactions with photons.
The other way to interpret it is the classical rotational motion of macroscopic bodies. Such bodies would have formed about 300,000 years AFTER the big bang (see above), and thus their rotational motion says nothing about the big bang itself.
Regardless of it’s original speculative purpose, I do believe the open/close universe folks use this as a deciding factor.