Assuming that the widely accepted Big Bang theory is true, the massive explosion cited in that theory would send matter speeding in every direction. Following this line of thought, there must then be a center of the universe - is this true in any way?
There is no center. The Big Bang was not a localized explosion that flung matter out into pre-existing space. It happened everywhere. It was the birth of space, time, and matter. You can say there is no center or that every point is the center. No matter where you are, things are receeding at a velocity proportional to the distance from you.
I heard an anology before that it’s similar to blowing up a balloon. If you put dots all over the ballon (representing galaxies) and then blow it up, all of the dots are moving away from each other - no one dot is the “center”, they all are.
It’s not the best analogy, given that the universe has more than two dimensions, but it helped me wrap my brain around it a little.
This has always puzzled the hell out of me. If pre-existing space didn’t exist, what did the universe expand into?
It didn’t expand into anything, it expanded into nothing. You just have to accept the fact that the human brain did not evolve to be able to intuitively understand nothingness, and you will always have difficulty wrapping your mind around it.
Sorry, I posted prematurely. In the baloon analogy, there is space outside the baloon for it to expand into. I don’t understand how the baloon could expand if there was no space for it to expand into. I’ve been told that what we experience as space is inside the baloon, but still it would seem to me there would have to be some empty space for the expansion to occur.
My step-father always used to say in regard to the big bang which gave birth to all we know as space and matter: “Something had to be there. What banged? And how did it get there?” 
Sorry, Thaumaturge. Your post came in while I was composing the last one.
No problem.
I agree, something had to be there, some basic energy matrix to give the bang something to play with. Myc current favorite theory is the epyrotic theory, which gives more of a framework for the universe to exist in.
Well, it’s better to start by not thinking of it as expanding.
Instead of the classic “balloon” analogy, think of space as a one-dimensional rubber band. As it streches, marked points spread out so we’re in the same place we were before.
Now, stack a bunch of rubber bands on top of each other, each one a little more streched than the last. You’ll get a bowl-shaped surface, where “space” is going around the bowl and “time” is going up the bowl. The “expansion” is only happening because there’s a definite direction everything is moving (up the bowl) as time goes forward.
The center of the universe is your local cat. Just ask the next one you see.
I still don’t get it. (Actually, I haven’t got it for quite a while).
Are you saying that the universe is like the video game Asteroids ©? That is, if you travelled in one direction long enough, you would eventually end up where you started? Is this necessarily the case? How does this fit in with the universe-as-a-saddle story?
If that is the case, would the travel-time for a given velocity be lower for a younger universe? That is, is it meaningful to say that the universe is growing bigger over time? (The answer to this has to be, “yes”, right?)
If the universe is growing, does that mean merely that the space between galaxies is becoming larger? Or are all constituent objects within the universe growing bigger?
I can understand a not-space preceding the big bang (sort of - since there is no time before the big bang, “preceding” means little). After the big-bang occurs, is it meaningful to talk of a space outside the “shell” of expanding/exploding matter? That is, does space exist that has matter only to one side of it, but oblivion to the other? I suspect that if the Asteroids hypothesis holds, the answer would be, “No”.
Wait a second. Given that all galaxies appear to be receding from the Earth, how does it follow that the Big Bang would not be a, “localized explosion that flung matter into pre-existing space”?
Hm. Light from galaxies further away is older. Would it be possible to look at a very young Milky Way galaxy (or its precursor) if we had sufficiently powerful telescopes? I suppose we could see it from many different directions.
What force propelled all this matter apart anyway?
Excellent information, **Thaumaturge ** and Mathochist. I’ll check out the very interesting-looking link as soon as I can, and I’ll ponder the rubber-band analogy to see if I can wrap my strained brain around it. I have to confess that it still has me a little bumfuzzled, but it seems to be starting to make sense. Maybe by looking at it tomorrow after a good night’s sleep, things will be a little clearer.
It expanded into an adjoining but collapsing universe(s).
Let me rephrase that.
A localized explosion might be expected to produce a universe that looks different than our own: for one thing, it would have a hollow core in the center of a ring of expanding mass. (But what if our telescopes were not powerful enough to reach the hollow core?)
Anyway, what is the evidence against a universe where the proverbial rising loaf of raisin-bread is encased in a pre-existing space? Or is this Occam’s razor at work?
<<Nice Ekpyrotic Universe link, btw>>
Sorry, I’m having a hamster problem…How about my own analogy?
Where is the center? That’s not an easy question/answer to grasp for several reasons, but try this one. The universe isn’t shaped like a balloon or sphere. It is expanding more in some directions less in others and not uniform enough to say, this is center. Of course some folks will get into planes and dimensions etc.
But for a simple understanding it would be similar to you taking a wad of gum and blowing it into a bubble then (without popping it) mash it almost flat and then give a twist and maybe put a wave or two in it. Now keep blowing and twisting and turning etc.
So, Cypress the universe is that gum, not the air inside of it. Only on the gum is where any matter can exist. It is also reshaping and growing with each puff. So, you tell me now. Where is the center of that wad of gum?
Think of all three dimensional space collapsing into a single point. Now reverse the process and then you’re envisioning the big bang. Now, all points in 3D space come from the same originating point. From the point of view of all the points in our 3D space, each sees itself as the descendent of the original point. Each sees all other points splitting off from themself. All points sees themselves as the center of the universe. And this isn’t just an optical illusion, this is the reality of space (as per the pervailing consensus).
Peace.
Yes, I am the center of the universe.
Before I toddle off, I just want to say I’m still having trouble with all these analogies. Whether it’s a balloon, a stack of rubber bands, or gum, space still exists outside them.
I know that those of you who trying to educate me understand this and I appreciate your efforts to enlighten me, but to me it’s like trying to envision a coin with only one side.
At the moment, we don’t know for certain wether the universe is finite or infinite in size. If it is finite, everyone assumes it must wrap around on itself—it might work exactly like your Asteroids game, or the connection might be more complex. If the universe were finite but not closed, you’d run into the problem of a boundary—a place where there is space on one side and the other side isn’t well defined. This would violate the theory of relativity as well as common sense.
The universe is expanding slowly enough that any object smaller than a cluster of galaxies is pulled back together by gravity faster than the expansion of space can tear it apart, so won’t be enlarged by expansion. We can’t be certain this will always be the case—the expansion appears to be accelerating, and conceivably we might have a Big Rip Scenario.
This is actually a more interesting question than it might seem. If the universe is finite (and hence closed, with no boundary) then it is conventionally assumed to simply be growing larger without expanding into anything. This might seem unintuitive, but mathematically there isn’t any problem with a space not being contained by any other space.
However, this conventional assumption could very well be wrong. According to some versions of M-theory, which is a candidate for a physical Theory of Everything that’s been attracting attention recently, what we think of as the universe might have formed when two fundamental entities called branes collided with one another within a higher-dimensional space. If this is true, then our universe remains contained within that space. The expanding-balloon analogy would be completely appropriate in that case, except that instead of a closed two-dimensional surface expanding within a three-dimensional space, you’d have a closed three-dimensional volume expanding within, say, a ten-dimensional space.
This is very possibly true. Some people have searched for evidence of this, but so far they’ve come up empty.
A very good question. The conventional answer is the collapse of “scalar fields,” but this doesn’t explain how the energy got into those fields in the first place. Of course, there’s no guarantee that the Big Bang even obeyed conservation of energy. We have lots of examples in particle physics of conservation laws which hold in some circumstances but are broken in others.
(Some people think the conservation of energy is so obvious that for it to be broken would be inconceivable; in answer to this it’s useful to remember that until the mid-nineteenth century no one even knew that such a concept as energy existed.)
How about this:
Assume the universe winked into existence all at once. From our perspective, the universe would seem to be expanding, because light from increasingly distant objects continues to reach us. And the farthest back we could ever see would be to ‘creation’. But each year, we can see farther as more light reaches us from further distances.
But if you look in any direction, you can see just as ‘far’, because what you’re really seeing is the expanding bubble, with you in the center, of the visible universe.
Is that close?
In response (partially) to another of your posts, you don’t have to consider anything but the rubber bands. You could say that one of them “expands into” the next as time progresses, so you never need any space outside the stack for them to “expand into”.
Inside the stack, being carried along by the flow of time, it looks like space (the bad you’re on) is expanding (as it moves to the next band in the stack), but from outside the stack you just see one thing: the stack itself. That’s the hardest thing to get one’s head around in terms of “spacetime”: that everything takes place in spacetime and the equations are written in such a way that it doesn’t matter what’s “outside”, so (by Occam’s razor), there’s nothing there.
Really new theories are positing something “outside”, but I don’t know enough about them to debate the fine points. I think they might just push the problem back to “where did the embedding space come from?”