Where did the big bang happen?
August 29, 2007 10:37 PM   Subscribe

If wanted to arrive at the point in space where the big bang occurred, in which direction should I start traveling?
posted by wigglin to Science & Nature (32 answers total) 12 users marked this as a favorite
 
Stay exactly where you are.
posted by vacapinta at 10:53 PM on August 29, 2007 [12 favorites]


backwards in time.
posted by iamkimiam at 10:58 PM on August 29, 2007


You'd want to look at a bunch of stars, and triangulate from the amount of blue- or red-shift in their apparent spectrum. With enough readings, you should be able to work out the point from which they're all travelling.
posted by pompomtom at 11:02 PM on August 29, 2007




If wanted to arrive at the point in space where the big bang occurred, in which direction should I start traveling?

What an interesting question. However, vacapinta is exactly right. Assuming that the big bang happened in a point of space that you can actually visit, assumes also that there was a space outside of the single point of the big bang (meaning, it exploded outward from a point, and if you magically time-traveled to the time before the big bang, you could stand in this space outside of the single starting point and observe it happen).

But that isn't the case. There was no "outside," because everything in the universe existed inside the singular point of the big bang. And everything is now moving away from everything else.

So, yeah. Stay exactly where you are. You're already at the center. And that space located 10 feet away from you? That space was in the center of the big bang, too. The chair you're sitting on? All that matter was in the center, too. The electrons that carried this web page were all in the center, as well.
posted by Cool Papa Bell at 11:13 PM on August 29, 2007 [5 favorites]


Except that the centre you're at is not the centre centre.
posted by pompomtom at 11:18 PM on August 29, 2007


Here's a slightly fuller explanation.

pompomtom: I have no idea what you're talking about. The Hubble expansion is isotropic.
posted by vacapinta at 11:25 PM on August 29, 2007


CPB goes into a bit of why your question is meaningless. I'm going to try to expand on that.

The universe is not flat. Theory right now is that it's "finite but unbounded", which means that it is not infinite in size, but nonetheless there are no boundaries.

If you take a sphere and draw a circumference on it, then that circle is finite but unbounded. The line length is not infinitely long, and in fact its length can be calculated precisely if you know the diameter of the sphere. Nonetheless, there are no end points.

Space is the same way. It's folded, curved, and it wraps around. Ignoring GR distortions, what that means is that if you travel in a straight line long enough, you return to your starting point.

The length of your journey, however, won't be the same now as it was a billion years ago, nor a billion years hence. The universe is expanding. That doesn't mean that the edges are moving apart, because there are no edges. What it means is that the round-trip straight line I described is getting longer.

(More or less. I'm simplifying the hell out of a lot of stuff, and you can't actually ignore General Relativity.)

At the time of the big-bang, that round-trip length was zero. As I understand it, the theory is that at the instant of the creation of the universe, it was a mathematical point. Of course it didn't stay that way; it began expanding immediately. (Including a bit of "inflation" along the way.)

But since the original point was the entire universe, then in a real sense every place that exists now is where that original point was, since all of it was compressed into that infinitesimally small space at the beginning.

Which is why Vacapinta's answer is right: You are at that point now. So am I. So is the Andromeda Galaxy.
posted by Steven C. Den Beste at 11:29 PM on August 29, 2007 [5 favorites]


I'd say you can visualize it by imagining space as a big rubber ballon whose size when deflated it zero. Now imagine that balloon being inflated. Since the entire balloon is expanding, it is easy to see that there is no point that it started to expand from.

If this balloon's surface was three dimensional, the analogy would be a lot closer to reality.
posted by philomathoholic at 11:34 PM on August 29, 2007




maybe it has a hole in the center
posted by hortense at 12:09 AM on August 30, 2007


The balloon is an OK analogy, but nowadays I prefer the Photoshop analogy. Balloons suffer from actually having a middle where all the air is, and there's no reason to think of the universe in the same way.

Imagine the universe is either an infinitely big picture or a tiled picture loaded into the graphics program of your choice. If you keep hitting the zoom out button everything keeps getting closer together, and by hitting zoom out enough times you can get any part of the picture to end up in the same pixel as any other part.

Now, it might look like you are zooming out from a particular point, but that's purely a result of which bit of the picture happens to be the middle of your screen. It doesn't really affect the picture at all, as you can scroll around it, and using scrollbars doesn't change the picture in any way. You've not really zoomed out around some central point, you've just rescaled everything.
posted by edd at 1:51 AM on August 30, 2007 [1 favorite]


...(Including a bit of "inflation" along the way.)

SDBC, That was the part in your excellent description that I wasn't able to follow. Would you be willing to expand (heh) on it somewhat more?
posted by Haruspex at 6:41 AM on August 30, 2007


Haruspex, wikipedia has an excellent article on cosmic inflation — it is a very brief period (perhaps 10-33 seconds) in which the early universe is thought to have undergone extreme exponential expansion.
posted by RichardP at 7:18 AM on August 30, 2007


Other than all this tesseract wackiness, you could always just travel to the point that all matter is going away from (the stars are all red shifted), since the universe is expanding, then start measuring the distance from the nearest stars in all directions to narrow it down. When all the closest stars are exactly the same distance from you, you're pretty damn close.
posted by IronLizard at 8:10 AM on August 30, 2007


the point that all matter is going away from

I should say the matter is escaping from at an equal rate, actually. Since everything is currently flying away from everything else.
posted by IronLizard at 8:17 AM on August 30, 2007


IronLizard - i don't know if you're joking, but the point everyone has been making in the thread so far is that no matter where you are, everything is flying away from that point (ignoring any local peculiar velocity).

read edd's description of zooming and think a bit.
posted by andrew cooke at 8:20 AM on August 30, 2007


I should say the matter is escaping from at an equal rate, actually. Since everything is currently flying away from everything else.

That point is still located wherever you are right now, as well as everyplace else. There is no center to the expansion.
posted by LionIndex at 8:20 AM on August 30, 2007


everything is flying away from that point (ignoring any local peculiar velocity).

If that were true, the phenomena of blue shift would never have been observed. That's not a 'local' phenomenon.

read edd's description of zooming and think a bit.

I did. This reads like some silly science fiction novel I read as a kid. Guy asks for a practical (ignoring the wild impracticality of actually implementing my insane plan) answer of how to find it, I give him one. If this single point doesn't exist, well, he never finds it.

It would be nice if we were all, every one of us, at the center of the universe. Hey, this is starting to sound like a religion.
posted by IronLizard at 8:34 AM on August 30, 2007


Interestingly, the universe was opaque to radiation until about 400,000 years after the Big Bang, when all that neutronium separated out into protons and electrons. Right at that moment the universe was flooded with radiation, which reflected the temperature of the universe at that time; but as the universe expanded, the wavelength of this radiation dropped.

That radiation is still here, all around us; we are bathed in the light from that primordial explosion. What direction is it coming from? All directions equally?

As it turns out, no. And the unevenness of this radiation tells physicists about the shape of the universe.
posted by ikkyu2 at 9:16 AM on August 30, 2007


SCDB: I'm a not a cosmologist, but I do enjoy it when they give department colloquia. I didn't realize that there was a consensus that the universe was finite and unbounded, since I thought the data was consistent with flat, and thus not finite. Could you point to any articles that talk about this?
posted by Schismatic at 9:47 AM on August 30, 2007


SCDB As I understand it, the theory is that at the instant of the creation of the universe, it was a mathematical point.

I'm fairly certain Big Bang theory makes no statements about t=0 but rather about t seconds after the Big Bang in which t is a smaller and smaller amount of time. We can extrapolate back to the Planck era which is about 10^(-40) seconds but who knows what the Universe was doing before that. String theory puts forward some possible answers but none of them include mathematical points.
posted by vacapinta at 9:57 AM on August 30, 2007


If that were true, the phenomena of blue shift would never have been observed. That's not a 'local' phenomenon.

Actually, it pretty much is a local phenomenon. The basic idea is, before the big bang, all space was contained in that one point where the big bang happened. Space itself is expanding out from that one point. There is no point in the universe that was not at that one point where the big bang happened.
posted by LionIndex at 9:57 AM on August 30, 2007


everything is flying away from that point (ignoring any local peculiar velocity).
If that were true, the phenomena of blue shift would never have been observed. That's not a 'local' phenomenon.


ignore peculiar velocity in general, then.
posted by andrew cooke at 10:07 AM on August 30, 2007


Argh. So the distance from, say, our star to the (Milky Way) galactic center is specific, but to the edge of spacetime (determined by background radiation) is essentially the same from any location?

I suspect that's a pretty stupid question, but I tend to need visual models to understand things, and this may not allow for that.
posted by Haruspex at 11:20 AM on August 30, 2007


background radiation does not determine an edge to spacetime. background radiation is a local thing, in that the photons are here now (or we wouldn't be able to detect them!).

if you look back far enough then (ignoring inflation) then any point on the sky was very close to any other place, because that far back the universe was much smaller. remember that looking out in distance also means looking "back in time". so in a sense all the background photons came from "the same place" which is "here", when "here was much smaller".

apart from the obvious difficulties here there's a real problem that requires inflation to explain fully, so i don't think you can hope to understand it completely (i don't).
posted by andrew cooke at 11:45 AM on August 30, 2007


Depends on what you mean by "the edge of spacetime"...

Remember, when we look out into the Universe we are also looking backward in time so the "distance" to the background radiation is a space-time distance and so its a distance to an earlier event in our Universe.

Likewise, if you look in one direction in the sky and see some galaxy and then turn your head in the opposite direction and look at a distant galaxy, those two galaxies were probably much closer to each other and in fact may even be the same galaxy.

So, everywhere you look, you are looking at an earlier Universe. One thing this means is that the most advanced pieces of the universe we can see are right here - we, ourselves and our own galaxy. For all we know, there are no other galaxies out there - they all blew up for some reason millions of years ago.
posted by vacapinta at 11:46 AM on August 30, 2007


..er, or what andrew cooke said...
posted by vacapinta at 11:49 AM on August 30, 2007


Yup, I find that inflation issue to be pretty damn near incomprehensible. But nonetheless fascinating and worth further study.

As always, I'm delighted that there is an immense amount of attention and consideration given to these topics, regarding it as one of humanity's better attributes.

That probably sounds dorky, but whatever. It's cool.
posted by Haruspex at 12:08 PM on August 30, 2007


There isn't any "edge" to space time. The analogy to the surface of a balloon is a good one. The balloon expands, but there isn't any edge on the surface of the balloon.

As to how fast things fly apart, the further away something is, the faster it's measured as going relative to us. See "Hubble Constant".
posted by Steven C. Den Beste at 12:42 PM on August 30, 2007


Just to expand on that a bit (ahem), the consequence of Hubble Expansion is that no matter where you are in the universe, it looks like nearly everything is going away from you.
posted by Steven C. Den Beste at 1:24 PM on August 30, 2007


This bit of recent news may or may not be tangentially related to this question.
posted by IronLizard at 3:14 PM on August 30, 2007


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