# What is our location relative to the Big Bang?

Given what we know about space, time and the movement of galaxies, have we or can we determine what our position is in relation to the projected location of the Big Bang? I've read some introductory papers on the superstructure and galaxy cluster movements, but none of them specifically mentioned space in terms of relative or absolute positions relating to the original position of the Big Bang.

So my question is, does our current understanding of the structure and workings of the Universe give us a good enough estimate to determine our location relative to the Big Bang or can we never guess at it, since every viewpoint in our universe looks the same in every direction?

Current cosmological theorists suppose that the universe is exactly identical, no matter where it is viewed from, so long as it is viewed at the same time. At the time of the big bang, the distances between any two given points seems to shrink to zero (or some nonzero value that we supposedly will derive from quantum mechanics). The conclusion is that the Big Bang happened everywhere, all at once.

This is also how you get out of the 'was the big bang a black hole?'-type questions: even though you had large concentrations of matter at times close to the big bang, they were spread out over all space, which is different than just having a clump of matter with finite extent (the second thing would collapse to a black hole).

• That's kind of what I expected the answer to be, but was unsure of where and how to check it. Though I am still a bit puzzled as to how the compressed space in the early universe prevented singularities from forming and allowed matter to escape and fill the voids, that's probably best left to a question of its own. – Klemen Slavič Dec 30 '10 at 14:05
• @Krof: the big bang is properly considered a singularity, too. It's just a qualitatively different type of singularity from a black hole singularity. In a spacetime containing a big bang singularity, ALL observers' histories end at the singularity. IN a spacetime with a black hole, only some observers' histories need intersect the singularity, and therefore, only some of them will end. – Jerry Schirmer Dec 30 '10 at 14:33
• And yet, after reading your answer I want to ask "Do we know where's universes center of mass?" If it is limited it should have one – Dmitry Dzygin Dec 30 '10 at 15:58
• I hate to reuse this image, but...sigh...imagine that the universe is the surface of a balloon that is being inflated. The 'Big Bang' is when it started out very small. It did not happen at any particular place in the universe (the surface of the balloon)! And most importantly, UNLIKE the balloon, there does not have to be any physical 'space' surrounding the balloon. There is just the surface of the balloon. You may ask 'where is the space around the balloon?' and I don't have to answer! – Greg P Dec 30 '10 at 17:02
• @Dmitry: center of mass has meaning only in flat universe. Mathematically, it requires the notion of integration of vectors. But there is no such notion in curved space-time. Imagine a surface of a balloon. Where is it's center of mass? The only reasonable answer would be in the center of the balloon. But that point doesn't lie on the surface and so that question just doesn't make sense from the surface's point of view. – Marek Dec 30 '10 at 17:15

Think about the big bang like this: if you took every possible trajectory that an object could possibly take through the universe, and traced them all backward in time, they would all eventually come together. That "merging of trajectories" is the big bang; all objects, and indeed all of space, would have been at the same position. So there's no one point in the universe that can be considered the location of the big bang.

More quantitatively, the FLRW metric, which is how we characterize the universe as a whole in general relativity, includes a scale factor $a$ which characterizes the relative scale of the universe at different times. Specifically, the distance between two objects (due only to the change in scale) at different times $t_1$ and $t_2$ satisfies

$$\frac{d(t_1)}{a(t_1)} = \frac{d(t_2)}{a(t_2)}$$

Right now, $a$ is getting larger with time. But if you imagine running the universe's expansion in reverse, eventually you'd get back to a "time" when $a = 0$, and at that time all objects would be in the same position. That's the big bang. (Adapted from another answer)

Our location is around 13.7 billion light years away from it in time.

• The light year is not a unit of time. (Unless you use geometrized units where $c=1$, but then why not just say "year"?) – David Z Apr 10 '11 at 22:25

I think Henry made these two minute physics videos(Where Was The Big Bang? and Science, Religion, and the Big Bang) specially for you:

As a short answer, the big bang happened everywhere! So anyone, anywhere(to be super cautious and conservative in an inertial frame) can say I have been at the center of the Big Bang :)

It is theoretically possible, but quite difficult to determine the position where we would be if our proper motion had zero speed.

The local group to which our galaxy belongs has proper motion of about 61 km/s. Our galaxy and Sun inside galaxy has even greater speed, but the direction is changing as Sun completes its revolutions about the galactic center.

So combining all these speeds and reversing all the dynamics back you will find a point where our Earth would be if it did not move since the Big Bang.

But you will find nothing special there.

Possibly it will be roughly in the direction opposite to the direction towards Great Attractor.

Big bang happened somewhere in the middle... edges... and everywhere at once.

• -1, it's Andromeda Galaxy – voix Dec 30 '10 at 18:38
• @voix +1 I just love this comment. – user68 Dec 30 '10 at 20:26
• you are missing the "all the good stuff is over here" caption pointing to the opposite side of the galaxy... – Michael May 22 '13 at 15:45
• I didn't downvote, but This iisn't very explanatory. – Abhimanyu Pallavi Sudhir Jul 6 '13 at 14:57

## protected by Qmechanic♦Jan 4 '13 at 5:32

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