Cosmology question.

Will we ever be able to pinpoint the approximate position of the big bang? Since everything came from one single point less than an atom in size I assume we’d never be able to locate the exact point, but, say within a light year?

-XT

I’m pretty sure they already can. All the galaxies are on the move. All you’ve got to do is find the point they’re all moving away from.

I can point precisely to exactly where the Big Bang happened: right where I’m sitting. Right where you’re sitting too. And under the President’s chair in the Oval Office, and on Alpha Centauri, and in the exact center of the Virgo Cluster.

This is one of the common misconceptions about the Big Bang (which is admittedly exacerbated by the explosion-evoking name). The Big Bang was not an expansion of some small bubble that contained the Universe into something else. Rather, it’s best to think of it as a sudden expansion in space itself. If you watched two objects at rest near each other shortly after the Big Bang, then as the space between them expanded, they would have more and more distance between them — not because they’re “moving apart from each other”, but because the space in between them is actually expanding. This sudden expansion of space happened everywhere in the Universe, and so it’s legitimate to say that the Big Bang happened everywhere in the Universe at once, hence my opening paragraph.

Pretend that I said what MikeS said, instead of what I actually said.

Sure. I understand the concept. However, I’ve seen theoretical models showing the expansion by running time backwards, so, at least in theory, you SHOULD be able to pinpoint approximately where the original expansion started from. Or, at least that’s the question I’m asking in this thread.

-XT

And you can pinpoint where the original expansion came from. It came from everywhere. That is, absolutely, completely, and unambiguously, the answer to your question.

Ok. Thanks.

-XT

Another way of saying it would be that at the instant of the BB, all “positions” were created, and initially they were arbitrarily close together. Since then the universe has been expanding, which allows the concept of distance to have some useful meaning.

There’s no ***where ***for the Big Bang; there’s only a when.

To say in another way what others have been saying, space itself was created by the Big Bang. The Big Bang didn’t happen in space, so it’s meaningless to ask where in space it occurred.

The balloon analogy helped me understand this. Draw a bunch of dots on a deflated balloon. Then slowly fill it up. All the dots move away from each other as the balloon expands, but there is no central point they are moving away from.

Yes, but don’t make the same mistake I made with this analogy. On the balloon the dots themselves expand as the balloon expands. In reality, galaxies get farther apart, but they themselves don’t expand. I had thought that ***everything ***was expanding, all the way down to subatomic particles . . . which pretty much means that nothing is expanding.

But another aspect of this analogy is that you can get to the “origin” of the balloon by going from 2D to 3D, toward the center of the balloon. Then your “big bang” would be the original uninflated balloon. So we can only get to our Big Bang by going from 3D to 4D . . . there’s an origin in time, but not in space.

Local forces can overcome the force of the expansion of the universe. Things bound strongly enough together by gravity don’t move apart as the universe expands, because the gravity is keeping them together. Things bound together by electromagnetic forces (that’s most stuff you deal with on a day-to-day basis) don’t expand with the universe, because the electromagnetic forces overpower the expansion.

It’s not an expansion in space, it’s an expansion of space. A lot of people think of it as a big fireball in space, spewing stuff out into space. That’s wrong. It’s space itself being created and expanding. This is counterintuitive, because most of us don’t deal with the concept of space itself expanding in our everyday lives.

But expansion overcame gravity at some point, right? Otherwise, wouldn’t everything in the Universe still be compacted in one lump?

There’s not enough stuff for gravity to overcome the expansion altogether. We used to think there might be, and that the universe would eventually stop expanding and start to contract, but most astronomers don’t think that now.

I think the OP is getting at the intuitive notion that, because space is expanding, there should be a current point from which everything is expanding “outward.” It is this notion of the shape of the universe being an expanding 3-dimensional sphere with a center point which is incorrect. Probably.

Everything, including space, is on the surface of the balloon (if you use that surface to represent how the universe is expanding). Exactly what that shape is–the overall curvature, so to speak–is currently a matter of conjecture.

Yes; everything is moving away from everything else, not away from some central point.

A visual aid I like to use: Make an overhead transparency showing a whole bunch of randomly-scattered dots. Now make another transparency with the same pattern, but zoomed in about 10%. Pick any point on the first transparency, and line it up with the corresponding point on the second transparency: You’ll see pretty clearly that everything is expanding away from that point. But now, pick any other point to line up, and you’ll see that everything is expanding away from that point, too. Now, picture the same thing, except with the two transparencies infinite in size.

Exactly. Space is the surface of the balloon, not the overall volume of the balloon.

The misconception is helped along by those artist’s conceptions of the Big Bang seen from outside, like this one (Not picking on them- it was one of the first Google Images results, and it’s pretty). That’s not what you’d have seen if you could have somehow been there at the time of the Big Bang. There would have been no space outside the fireball to look at the fireball from- you’d have had to look at it from the inside, because there was no outside.

We’re pretty sure it’s not something that most people could visualize easily. It’s not something intuitive like a sphere.

I’m not a cosmologist, so forgive me if I say something stupid, but I’d like to address this specifically.

I theory, if you could run a movie of the life of the universe backwards and watch, what you would see is everything hurtling back toward you. You would be in the exact center of the baby universe, and everything expanded out from your position.

But someone five billion light years away would also see everything moving back toward them, and they would be in the exact center of the original tiny universe as it began to expand.

And so it would be from everywhere.