Which way is the center of the universe?

At the Astronomy Picture of the day, a few days back, I saw a map. The map indicates that the Local Group moves at about 600 kilometers per second relative to [the Cosmic Background Radiation.]

I know that the image of all the stars and galaxies exploding out into space at the Big Bang, and rushing outward from the center of the universe after that is inaccurate, and simplistic. My problem is that I now find that it seems that we are doing just that. How come the direction toward which we are moving isn’t “away” from the big bang, and the direction from which we came “toward” the center of all things?

Just when I think I am getting a grip on this whole cosmological mystery, and learning to appreciate how subtle the real answers are, it turns out it might just as well be boom, whiz, fizzle, just like I thought in fifth grade when I first heard about it all.

I am confused.

Sorry, I thought you were asking for directions to my house.


My grasp on this is a little shaky but AFAIK there are two factors to consider. First space itself is expanding, and as such we are actually already at the place where the big bang happened. Second, since that time lumps of matter (galaxies, groups of galaxies) have been interacting and adding relative motion.

I really hate analogies and this one is totally inaccurate in many respects but let it go and consider this: Take a pool table where the felt is made of stretchy rubber. While you are playing pool someone is stretching the table in all directions. Bad analogy I know, but here the table is space and the balls are the galaxies, groups of galaxies etc that are interacting with eath other.

By the time you have stretched the table to a few thousand kilometres the net result is that it is pretty meaningless to talk about a centre because the bits that were the centre have been strectched and are still all around you.


It’s hardly surprising that on a local scale, objects are moving relative to each other, is it? After all, the earth is moving around the sun, the sun around the galactic centre. Although the universe is expanding, some nearby galaxies are blue shifted, meaning they’re currently moving towards us. But your general understanding of matter moving apart on the large scale is correct. Still no centre.


As you suspected since childhood answer is: You are at the center of the universe.
In other words, every point appears to be the center of the universe from that point. This makes absolutely no sense to me either, but the universe doesn’t have edges and has way more than 3 dimentions so its kind of like a moebius strip.

If you want the gruesome details check out:

Warning, unless your a cosmologist, reading this material may cause smoke to start shooting from your ears!

I’ll have to think on this one. Maybe one of the physicists or actual astronomers here can help out. Following the links within your link, it doesn’t seem like the map indicates any kind of center to the universe.

Here’s the most helpful text I found from those links…
(from http://zebu.uoregon.edu/~js/glossary/cosmic_microwave_background.html )

doesn’t directly answer you question, but I think the answer spins off from there somehow

If the Universe is expanding what is it expanding into? Is there only one Universe? Was there only one really big bang? Would we expect galaxies from two distant bangs to one day mingle.

The word expanding presumes there is a size. How would one measure the size or change in size? If it is expanding into nothing, isn’t that still part of the Universe?

The simplest way to think about it is that everywhere and nowhere is equally valid to consider the center.

Even though we can measure velocity relative to the background radiation, this does not imply a center. Going by the proposal in the OP, if where we’re going is “away” and where we came from is “toward”, then what about a hypothetical object traveling in the opposite direction? It will also have a velocity relative to the CMBR, yet by your conventions would still be travelling “away” from the center.

As has been said many times here, the universe is not expanding into anything. Space itself is expanding, and the whole of space is what we consider the Universe. This is a distinct concept from matter in the universe being flung out to regions where it wasn’t previously, because in that case those regions would already exist.

The concept mentioned by Mashie of multiple (spatially distinct) big bangs misses the point. At the big bang, everything that existed was in a very small space (possibly a point), and there was no other space. The big bang was not an explosion as seems to be commonly thought.

Well, “no edges, no borders” certainly is one theory. To answer a few of your questions, imagine an ant walking along the surface of an expanding bubble. The 2 dimensional surface of the bubble is the ant’s universe. This two dimensional universe has no edges or borders and is finite in area. What’s the ant’s universe expanding into? A third dimension. Every point on the bubble is moving farther from every other point as the expansion progresses.

By analogy, our 3-dimensional universe can be considered to be expanding into a 4th spacial dimension (that we can’t percieve, just as the ant only comprehends it’s two dimensional universe while travelling on the surface of the bubble).

Is there only one universe? There are plenty of theories that argue both sides of this, although I’m not intimately familiar with any of them.

Was there only one big bang? For our purposes, yes. Perhaps in reality, the overall history of the Universe has consisted of Big Bang, expand, stop, contract, Big Crunch, and repeat, but for our purposes currently, time is defined as starting at the Big Bang. So, to ask “what happened before this?” is a meaningless question in the realm of physics since time as we perceive it did not exist before the Big Bang. Also, bear in mind that the Big Bang happened at every point in the Universe simultaneously, so that every point in space is moving away from every other point.

I believe the change in size is determined by taking measurements of the red shift of stars. A greater magnitude of red shift corresponds to a more rapid rate of expansion.

Don’t know how accurate this is, but a college chemistry professor defined the Universe as being a closed system. Thus, the space into which the Universe was expanding would not be considered part of the Universe in which we reside.

Reading TheNerd’s post, I realized I made an error in saying that the space into which the Universe was expanding was not part of the Universe. TheNerd is of course correct; there is no space outside of the Universe, at least, not 3 dimensional space. Just as the 2 dimensional bubble-surface universe is expanding into a 3 dimensional space, not a 2 dimensional space, the Universe would be expanding into a 4 dimensional space, not the 3 dimensional space we perceive as being “space.”

Not quite. The 2D bubble is a model for an expanding closed 2D universe. The extra (3rd) dimension is an artifact of the model. It exists only to help you visualize. It is not necessary to suppose it has any kind of existence.

There is no space outside the universe.

You ask a good question. If the microwave background lets you determine a universal frame of reference, then in a way there seems to be a sort of absolute velocity, which quite spoils the idea of Gallilean relativity and all the others that have built upon it (including Einsteinian relativity). But I think this would make it sensible:

  1. You should interpret your velocity relative to the microwave background as velocity you have picked up since the Big Bang. If no other body (such as a massive galaxy cluster over yonder) had attracted you and accelerated you, you would have measured zero velocity relative to that microwave background.
  2. Everyplace is the center of the universe. Somebody a billion lightyears away who also had never been accelerated since the beginning of the universe would also observe zero velocity relative to that microwave background, the appearance of which depends on from where it is observed.

That being said, I don’t necessarily know what I’m talking about…

All velocity is relative to some frame of reference, but some frames just happen to be more useful than others. For instance, if I ask how fast my car is going, I probably want that relative to the Earth. If I want to know how fast the Earth is going, then I want it relative to something else. Basically, when we measure relative to the CMB, we’re measuring relative to the average velocity of all the stuff that happens to be a certain (very large) distance away from us. It’s a useful reference frame in many situations, but there’s nothing special about it.

The CMB radiation is a mighty big frame of reference.

Ok, so I am moving because the “Great Attractor” is pulling me along, and has been for a billion or six years. Every direction is symmetrical with respect to the center of the universe.

But it still feels like one incredible coincidence to me.

So, is anyone mapping the relative velocity of other stuff in the CBR frame of reference? (seems like a big problem in math, but nothing needing a breakthrough in theory.)

You might find this site answers the question at hand.


Please keep in mind, however, that there is no 4th spatial dimension into which 3 dimensional space can curve. The curvature of the universe is strictly an "intrinsic’ curvature.

O.K let me see if I have this straight. (Bare with me guys I’m new at this thinking stuff)
First the universe is expanding, but it isn’t really expanding into anything.
Second the space all around us is expanding while we’re moving through it making the center of the universe moot.

I guess I just don’t get it. If I was to hijack Captain Kirks Transwarp Enterprise and fly to the edge of the universe, the point where behind me is universe in front of me isn’t, and I looked out the window what would I see? Since there would be “nothing” in this un-universe would time still flow like in an Einsteinien universe? What would happen to matter as it entered? I have a big mental block when it comes to picturing nothing. What should I be picturing in my minds eye when I think about this “place”

The whole point of an intrinsic curvature is that there is no edge. The Universe has no more edges than the Earth’s surface does. Your question might make for an interesting novel but is moot under our current understanding.

J’s Friend - Either space curves back on itself (like the ‘walking the surface of a baloon’ analogy) or it’s infinite. So, you can never reach an end/edge.

Triskadecamus - What’s the coincidence? Space expands in all directions. So whether you are in Galaxy A or Galaxy B, you will see all other galaxies (except those in your Local Group) moving away from you. So each galaxy has the misperception of being at the center of the universe when, in fact, there is none.

just for S’s & G’s, here are some of our speeds measured to different reference frames…
The Earth is rotating on its axis at about 1,000 miles per hour (mph) (at the equator).
The Earth is revolving around the Sun at about 67,000 mph.
Our solar system is orbiting the center of the Milky Way Galaxy at about 500,000 mph.
Our galaxy is racing toward the “Great Attractor” at about 2,230,000 mph.
Anyone feel dizzy?

One thing I’m surprised you haven’t mentioned : the universe isn’t just expanding, it’s accelerating. This was proven after the invention of the 2df telescope. If it’s accelerating, what’s pulling/pushing it?..
(This kind of surprised astonomers who had two hypotheses, either the universe was slowing down, so that could predict when then big crunch would happen; or the universe was growing at a constant rate, in which case it would continue to grow ad nauseum)

(Various answers to the OP)

  1. The universe is a fractal of infinite intensity in multiple dimensions, including time. Thus, there is no centre, and even if it did have a frame of reference that could conceivably be called a centre, it may not exist yet.
  2. There is no spoon.
  3. It has been noted that black holes seem to be moving. Mostly towards certain points or lines in the universe. The points or lines are also moving. Wherever they shall meet : that may well be centre of the universe.
  4. Cornwall.
  5. Dark matter may exist. If it does it may give us a clue to the shape and structure of the universe as a whole.
  6. Impossible to tell.
  7. 15.5 billion years ago.
  8. etc