Okay. So, we know that the universe is expanding. It has been, presumably, since the big bang (or whatever the heck started this whole mess). But, the big question, is this. Presumably, there must be an edge of the universe, where the photons and other subatomic particles that exploded from the big bang are just now reaching. The universe is expanding, but into what? What lies beyond the edge of the universe? I know that it is impossible to make much other than a WAG, but have any scientists ever wagered a semi-educated guess on the subject?
Nope, no edge, no extra space, no nothing. Space-Time was created with the Big Bang, and the Universe is simply expanding by getting bigger.
To add a bit, new space is being created by the expansion of the universe.
Draw a line along the surface of a basketball. Keep the line going until you hit an edge. When you do so, I’ll give you a million dollars.
That’s just a fancy, SPOOFEy way of saying “There IS no edge.” (No, that’s NOT a Matrix reference.) If you were to head off in a “straight” line and travel trillions upon trillions of times the speed of light, eventually you’ll get back to the exact same point that you started at.
There’s no “new” space being formed. The existing space is being stretched out… interestingly enough, this results in a sort of “quantum blur” (I apologize, I don’t recall the exact term for the phenomenon) where tiny, tiny, tiny objects lose the definition of whatever edge they may have apparently had. To get an idea of what I’m talking about, get a deflated balloon and draw a smiley face on it, and then inflate the balloon. The smiley face will still be there, but it’ll be faded and blurred and… well… larger. And stretched.
That’s what’s happening to the universe.
The universe is infinite in size. If there was something else for it to expand into, it would have boundaries, and thus be finite. The universe - that is, space-time itself - is expanding, thus there isn’t any need for a ‘something else’ for it to go into.
Thinking about it makes my head hurt. I do want to semi-hijack by posting a related question.
Everything I ever heard about the Big Bang say it started with a very compressed little ball, something the size of… what?
if we take away all empty space in all the atoms in a star, there would still be something left, albeit very much smaller. Shouldn’t we be able to guesstimate how big the ball that started the big band was?
So … the universe is like an inflating balloon?
I’m still not quite sure that I get the concept. At the milisecond, just before the big bang, the universe was teeny tiney. Then, it exploed and got big. Shouldn’t there be an ‘edge’ of the universe’ just as there is an edge to anything else? Or, am I just not thinking umpteen-dimentionally?
The inflating balloon analogy illustrates how a two-dimensional universe would expand. To extend the analogy to our 3D universe we would have to talk about being on the 3D “surface” of an expanding four-dimensional “hyper-balloon”, which would not be very useful because it’s difficult/impossible to picture such a thing.
Usram has it. This whole question boils down to our effective inability to model things in four dimensions. We simply don’t have any exposure to anything remotely like it in our regular lives to base the model on. So unless you approach it from a totally abstract and mathematical viewpoint you’ll never really get your head around the concept.
So the inflating balloon is the best we can do.
It’s easier to think of it as staying the same size but the space between the things in it expanding.
Well the balloon analogy given recent obeservations doesn’t really work as the universe appears to be flat (as opposed to curved) and most likely infinte, though it could still be flat and finite if it were torus (‘donut shaped’) as opposed to spherical.
Another way of getting a good idea of how the universe can expand without expanding into something is from the fact that the famous astronmer (and ardent opponent of the big bang theory) showed that an expanding universe is apparently (i.e. observationally) the same as a universe where all the matter inside is shrinking.
At the big bang the entire observed universe was compressed into a point of infinite density (a singularity).
My current argument with the universe (it doesn’t argue back, so I’ll lay it on you people)
is that the expansion causes constant cooling; it is like a piston with a fixed volume of gas inside, with the cylinder head being withdrawn at the speed of light- the universe is effectively open in this case, isn’t it?
I mean - the Sun is pouring energy out into the black sky at a terrific rate; as those photons stream away into the universe, a certain proportion of them will never directly encounter matter, and so not be absorbed; they will just keep going as the universe expands around them
as if the universe were infinite…
that worries me- it seems so wasteful.
SF worldbuilding at
http://www.orionsarm.com/main.html
It was my understanding that there were approximately 384 people at the gathering when Glenn Miller began playing.
So what’s all this talk about the universe being infinite? A year or so, the standard answer here would be that it’s finite, but unbounded. I would think it’s just a typo, but a recent article in Scientific American stated that the universe is infinite, therefore likely contains an infinite number of other, uh, local universes (?), so there are other universes out there where there is someone who looks just like me, living in an exact duplicate world, except that guy is a good dancer and a hit with the ladies.
It might help to think of space and time as really two aspects of the same thing, which began with the big bang. Right now, at this very moment, we are at the cutting edge of time. There’s no “future” into which time is expanding, it’s just expanding, so that the “now” is constantly growing farther from the big bang. So the “edge” of the 3D universe is constantly growing farther from the big bang, though it’s not expanding “into” anything 3-dimensional.
It also might help to think of yourself as a 2-dimensional creature on the surface of a constantly-expanding ball. All you know is that you’re on a surface, and you keep traveling around, trying to find the “edge,” wondering what the balloon is expanding “into.” But no matter how far you go there’s no edge, and your path keeps crossing itself, and you keep returning to places you’ve already been to. If some 3-dimensional being suggested to you that you might try moving “inward” or “outward,” you might understand him theoretically, but you wouldn’t be able to easily wrap your 2D mind around those concepts.
Think of universe this way
- Visible Universe: Basically this is what we can visible observer with our instruments. Goes back about 14 Billion years, but we miss out on all the cool stuff that happened before the universe cooled enough that photons could avoid being absorbed
- Our Universe: basically the whole thing where the laws of physics operate. This is the universe of eth Big Bang, inflation, expansion etc. Its “bigger” than the visible universe due to the initial opaque stage of the universe
- Universe: The entire realm of the possible, where our universe and its laws of physics reside with others with laws that make you head hurt.
The infinite universe idea comes from number 3.
I want to elaborate on Gaspode’s question a few posts back. Supposedly, at one time, a millisecond before the big bang, the universe was the size of a small sporting ball. And then it exploded.
If that was the case, and everything was contained in this miniature ball, wouldn’t it appear, to the inside observer, to be the exact same size as ever? Our relational size would be the same.
BTW, I’m glad that someone was actually capable of suitably explaining the “expanding into nothing” and “4D” scenarios at a level that I could understand. Thank you.
Now that I think about it, what do the possible multiple universes coexist within? It isn’t space-time, so what is used to describe it?
“Before the Big Bang” is not a meaningful term. It’s like going to the North Pole and keep on walking north. And if the Universe is infinite (as currently seems likely), then it was already infinite at every point in time after the Big Bang. What the Universe was like exactly at t=0 (not before nor after) is probably a meaningful question, but it’s not one to which we have a meaningful answer.
All modern (20th century or later) models of the Universe consider it to be unbounded. Until a few years ago, it wasn’t known whether it was finite or infinite, but current evidence seems to be rather strongly favoring infinite. A finite but unbounded Universe could be the surface of a hypersphere, or it could be topologically nontrivial like an Asteroids screen where the “edges” are pasted together (there are a number of other possible finite-but-unbounded topologies as well, but I won’t get into them here). The Universe appears to be flat, which rules out the hypersphere possibility, but we can’t yet rule out the topological possibilities, which is why we’re not certain that the Universe is infinite.
And the visible universe isn’t limited so much by the fact that the Universe used to be opaque (we can “look” past the opacity using neutrinos or gravitational waves), but by the speed of light. No matter what method of observing we use, we can’t see anything further than 13.7 billion lightyears away, since that’s the age of the Universe. While it’s conceivable that the laws of physics might be different in different regions, nowhere in the observable universe have we detected evidence of any sort of gradient or discontinuity in the laws. So either we’re in a “special” place in the Universe (one far from any change in the laws), or there aren’t any changes in the laws, and physicists are loathe to accept that our location is “special”.
Chronos, a clarification, if you please: You state that current evidence suggests an infinite universe. However, while the evidence I am familiar with (which, granted, may not be all that’s available) certainly suggests a flat universe, I’m not aware that it has anything to say on the finite vs. infinite issue. Are you assuming an infinite universe because, given a flat geometry, Occam would say that it is the simplest topology, or is there some evidence that really does support an infinite universe? (My asthetics were really hoping for a finite universe.)