This question may seem a little vague, but, i will try to make it as specific as possible with what terms I am familiar with. Also, I guess none of these will apply if the universe is open(except for the last question), and that all of this is therefore hypothetical. How do we know where this universe (or the universe) ends. If there is something outside this universe, like maybe, another universe, would it have the same laws of physics, or different ones? If it does have a different set of laws of physics, can we define the edge of the universe as where our laws of physics stop working?
Also, how would we know if the universe is closed or not?
Most cosmologists would say the universe has no edge. It’s kind of a difficult concept for the human mind to grasp, but “beyond” the known universe there exists nothing; no time, space, energy or matter. While many have speculated on the existence of multiple universes, it’s just that: speculation. Since we cannot observe any other universes, they cannot therefore affect us in any way, and so can be effectively said not to exist.
But still, how do we know that the universe has no edge? and if from what i understand of the Big Bang theory, the universe exploded, so doesn’t that imply that the universe had an edge at one time? Or am I just misunderstanding the theory?
As I said, it’s a very difficult concept to grasp. If you can accept the idea that space cannot exist without time or dimension, that the concept of “nothingness” is just that, you’ll begin to understand what I mean. The universe encompases everything that exists, by definition, so one cannot discuss what is “beyond” it without wandering into the realm of metaphysics. Language simply fails us at this point, and one must accept certain concepts at face value. Unsatisying, perhaps, but that is all our limited minds can grasp. Ain’t cosmological physics fun?
No one on the planet knows. There are theories and models, but our ability to gather evidence for them is pretty miniscule when compared to the scope of the question. I mean, this is one of The Questions. You might as well ask “What Is The Soul?”
I understand that that if there isn’t an edge to the universe, we can’t know it, and if there is an edge, we can’t pass it, but isn’t there some sort of debate as to whether the universe is open or closed?
The universe has a limit- a different thing…
if you look at the Hubble Deep Space Field photographs, you will see ancient galaxies up to 10.5 billion of years old and of course 10.5 billion ly away from us.
What is * between * those galaxies? are there smaller images of even more distant galaxies 20 billion ly away?
No.
The Limit of the universe is about 15 billion years ago, and about 15 billion ly away in those images. All you get from that distance and that time is the Background radiation, an echo of the Big Bang itself. We only get a small amount of this big bang radiation, because the universe has expanded so much that most of itis forever beyond our reach, beyond an effective event horizon in the sky.
You are never going to find out the full extent of the original big bang so you can stop worrying about it.
The debate on whether the universe is open or closed doesn’t revolve around its boundaries, but rather whether it will continue to expand forever (open) or eventually reverse its expansion and collapse in on itself (closed, a Big Crunch). Currently, with available evidence, cosmologists do not believe there is sufficient matter in the universe to reverse the expansion, so the universe is open and will expand forever, continuing to cool as it does so, eventually reaching an average temperature of near absolute zero. Eventually, all the stars will burn out and we’ll be left with a cold, dead universe. The universe could still be closed, but as we gather more and more evidence, this seems increasingly unlikely.
Thanks Q.E.D. Apparently i did misunderstand something, but if it was plausible that the universe could crunch together, doesn’t that mean it does have boundaries? Or am I still missing something? I knew about the whole Big Crunch thing, I have some old S.F. magazines laying around somewhere with something about that in them. Anyway, since my post was misunderstood, when I said closed or open, I meant boundaries, not whether it will stick around for all of infinity or if it will collapse again.
No, even if the universe is closed and will eventually “crunch” in on itself, it still doesn’t have a boundary, per se. The concept I’m trying to get across is that, although the universe is of limited dimension, it has no boundary. That seems very counterintuitive, and it is. the universe has been likened to the surface of a balloon being blown up: as it expands, points on its surface get farther away from each other, and there is no center (ignoring features like the opening you use to blow air in). If you can accept that there isn’t anything that is beyond the surface of the balloon, you’ll have the general idea.
I get it now. Thanks again.
/hijack?
so what about the shape of the universe? is it known? is it shaped like an egg sunny side up? does it rest on a plane?
The shape is as moot a concept as the boundary. Since a shape is defined by a boundary, without a boundary, you can’t have a shape. Our limited senses seem to perceive it as being spherical, but in reality, there really isn’t any shape to it. My head hurts now…
I raised a similar question here.
I think there was a concensus that the Universe does have a boundary - upto this boundary we can effect (or measure) “bodies” but beyond this boundary - we cannot know or say anything about bodies.
Since matter constantly moves out of the universe (which does’nt happen on the surface of a blowing up baloon), its not certain whether the universe’s entropy is increasing or decreasing. That is contrary to what we learn in thermodynamics that the entropy of the universe keeps increasing with time.
I disagree; the surface of the earth is boundless, yet it has a shape, the screen in an Asteroids arcade game is boundless, but it has a shape; of course whether it would be possible for the flatlander inside the spaceship in the Asteroids game to discern the shape is another matter entirely, but certainly they would be able to know when they had wrapped around and visited the same point twice, which is a start.
Nice one, Squink; I was thinking of posting a link to the Donut theory myself.
Homer Simpson Cosmology…
It might even be that with a big enough telescope you could see the back of your own head.
I really really don’t want this one to be true.
What is the shape of the Asteroids "universe? Locally it is flat. Globally, its topology is the same as a torus (doughnut). But a torus is curved, and on a flat surface you can’t go off in one direction and return from another.
I thought a torus was donut shaped. Asteroids, if I remember correctly, did not have a hole in the middle of it. Wouldn’t it be some sort of a contorted sphere?
Um, but you can. The “Asteroids universe” is an example of a flat surface where you can go off in one direction and return from another.
“Flat” is, as you correctly noted, a purely local condition. But whether or not you can go off in one direction and return from another has everything to do with the topology of the surface, which is a global condition (again, as you noted). Or, to put it another way, a torus doesn’t have to be curved; it’s just that our usual picture of a torus in three dimensions is curved.
(Mindless side note: I always think of “Robotron” as my videogame example instead of “Asteroids”, for some reason…)
XWalrus2: what DrMatrix is saying is that the “Asteroids universe” is topologically the same as the surface of a doughnut, and the hole in a doughnut isn’t in its surface. Imagine that the videogame was taking place on some kind of flexible rectangular sheet. Since you can walk off the left side of the game and reappear on the right, bend the sheet into a tube so that you can glue the left and right edges together. Now you have a cylinder, but you can still walk off the top side of the game and reappear on the bottom, so bend the tube in the other direction so that you can glue the top and bottom edges of the cylinder together. Now you have a torus-shaped surface.