PDA

View Full Version : Location of Big Bang



DaveH
2009-Feb-16, 04:46 PM
We all know of the Big Bang Theory. We also know of the expansion of the universe as a result of the Big Bang. However, I have not heard just exactly where this Big Bang took place. If the universe is expanding in all directions from the point of the Big Bang we should be able to locate where that center point is. So, where is this point in the universer? Billions of lights years in the direction of Orion? Or maybe out in the direction towards Polaris? I'm sure I just missed this piece of information. Anyone know where the Big Bang took place in the Universe?

stutefish
2009-Feb-16, 05:00 PM
The Big Bang happened everywhere.

Where's the center of the surface of a sphere?

gzhpcu
2009-Feb-16, 05:19 PM
Welcome to BAUT DaveH,

According to the Standard Big Bang Theory, our universe started out as a very small (theorectically, infinitely small) point, from which the BB started. When it started, spacetime also came into being and started to rapidly expand. Like the expansion of a ballon (as stutefish mentioned), whereby the surface of the ballon is the edge of the universe. Therefore, since everything was initially together, the center is everywhere.

Sam5
2009-Feb-16, 05:32 PM
We all know of the Big Bang Theory. We also know of the expansion of the universe as a result of the Big Bang. However, I have not heard just exactly where this Big Bang took place. If the universe is expanding in all directions from the point of the Big Bang we should be able to locate where that center point is. So, where is this point in the universer? Billions of lights years in the direction of Orion? Or maybe out in the direction towards Polaris? I'm sure I just missed this piece of information. Anyone know where the Big Bang took place in the Universe?

Nobody knows.

DaveH
2009-Feb-17, 05:41 AM
I get the 'no center for a surface of a sphere". However, the sphere encloses a volumn that must have a center. This is what I am looking for. This is also the starting point or the originating point of the Big Bang.

لطفيّ
2009-Feb-17, 06:03 AM
I get the 'no center for a surface of a sphere". However, the sphere encloses a volumn that must have a center. This is what I am looking for. This is also the starting point or the originating point of the Big Bang.

I'm with gzhpcu that it is everywhere. But I would change the wording to say not that the surface of the sphere is the edge of the universe - it is the universe.

This surface of a sphere is an analogy, but the idea is that we can act like the universe is a surface in a higher dimensional space. So the geometry of the universe can be like the geometry of the surface of a sphere embedded in a higher dimensional space, and there can exist a center of the sphere in this higher dimensional space. But this center does not correspond to an actual place in the universe - it is outside the universe, it exists only in our minds.

m74z00219
2009-Feb-17, 06:11 AM
The analogy of the surface of the sphere only goes so far I think. The Universe (the Level One Multiverse) is infinite in extent. Part of the reason we're at the center of the observable universe is because everywhere in this Level 1 multiverse is the center of it.

Check this out for information about the Level 1 multiverse.
http://space.mit.edu/home/tegmark/multiverse.html

nauthiz
2009-Feb-17, 06:25 AM
I get the 'no center for a surface of a sphere". However, the sphere encloses a volumn that must have a center. This is what I am looking for. This is also the starting point or the originating point of the Big Bang.

The center of the volume enclosed by the surface of a sphere (which is a two-dimensional object) doesn't reside in the surface of the sphere; you have to travel through a third dimension to get there.

I'm dangerously close to overstretching the analogy here, I realize, but consider that it could be a similar situation for the universe and the big bang. We don't really know of any dimensions beside the usual three, so the idea of a place that we can't get to by traveling within those three dimensions is non-sensical. Similarly, the balloon analogy is meant to be limited to two dimensions - within the context of that analogy, talking about the interior of the sphere is non-sensical.

BigDon
2009-Feb-17, 06:37 AM
Nice answer Nauthiz.


(Do I owe you an apology? I recall being snarky to you a couple weeks ago, but I can't remember over what.)

Ufonaut99
2009-Feb-17, 07:16 AM
I've alwyas imagined the sphere's radius as being Time, but as you say that could be pushing the analogy too far (especially if you start picturing a BigCrunch)

antoniseb
2009-Feb-17, 09:55 AM
I agree with many of these explanations, and also that the analogy is easy to stretch thin. I like to make the point that concepts such as location are useful and comprehensible when working with tiny fractions of the universe and a small section of all the time that ever was, but that as you approach talking about the whole universe for its whole history, some ideas stop being comparable to common everyday experience, and defy description with common linguistic techniques.

DaveH
2009-Mar-03, 12:46 AM
So what I am hearing from this community is that everywhere/anywhere in the universe is the apparent center. This makes no sense no matter how many dimensions you conjure up. In a galaxy 13 billion light years away from us; an entity residing on a planet orbiting a star looks out into the night sky and sees other galaxies 13 billion light years away no matter where it looks is very difficult to conceive of, but this is what you all are saying. I think I am getting the Dark Energy/Matter explanation of why gravity doesn't explain the movements of galaxies and the expansion of the universe. Just make something up to cover our ignorance. It's almost mystical in nature. A spiritual entity ruling the universe makes about as much sense. Can't someone just say "we don't know why the center appears to be anywhere"

Amber Robot
2009-Mar-03, 12:54 AM
I get the 'no center for a surface of a sphere". However, the sphere encloses a volumn that must have a center. This is what I am looking for. This is also the starting point or the originating point of the Big Bang.

You do not need to embed a 3-dimensional space inside a 4-dimensional one (a la your balloon analogy) to mathematically describe its expansion.

slang
2009-Mar-03, 01:05 AM
So what I am hearing from this community is that everywhere/anywhere in the universe is the apparent center. This makes no sense [...]

There is no rule that the universe should make sense to what is intuitive for humans. Remember that 'making sense' and 'intuition' are limitations of our brain, which from a very young age is being trained to deal with human scale reality, not with the vagaries of cosmic reality (or rather the scientific theories that describe it).

alainprice
2009-Mar-03, 01:59 AM
The center of the visible universe is wherever your detector is: eyes, ears, telescopes... here --> * <---

The center of the actual universe is expected to be nowhere and everywhere, in reality, one could exist right under our noses without realizing it. It all depends on the correctness of Einstein's Relativity.

If a galaxy that looks to be 13 billion light years away looked into the sky tonight and only saw galaxies on one side, THAT would be odd. Why should we be so special out of a trillion or so galaxies to be located at the center? We would hope they see the same kind of sky we do. But now we run into the next problem. How big is the universe? How much bigger is it compared to what we can see? Does it loop onto itself, à la sphère?

WayneFrancis
2009-Mar-03, 05:06 AM
I get the 'no center for a surface of a sphere". However, the sphere encloses a volumn that must have a center. This is what I am looking for. This is also the starting point or the originating point of the Big Bang.

The "centre" if you want to think of it that way would be in a 4th dimension that appears to be inaccessible to us.

WayneFrancis
2009-Mar-03, 05:19 AM
So what I am hearing from this community is that everywhere/anywhere in the universe is the apparent center. This makes no sense no matter how many dimensions you conjure up. In a galaxy 13 billion light years away from us; an entity residing on a planet orbiting a star looks out into the night sky and sees other galaxies 13 billion light years away no matter where it looks is very difficult to conceive of, but this is what you all are saying. I think I am getting the Dark Energy/Matter explanation of why gravity doesn't explain the movements of galaxies and the expansion of the universe. Just make something up to cover our ignorance. It's almost mystical in nature. A spiritual entity ruling the universe makes about as much sense. Can't someone just say "we don't know why the center appears to be anywhere"

What you are hearing and what is being said seem to be a bit different.

Yes if you go to any point in the universe it is expected that you would see much the same thing. Almost every other galaxy receding away from you.

This is because galaxies are not moving through space in a direction that is away from you but that space/time itself is being created between you and everything else in the universe.

Lets use the raisin bread analogy. Imagine that you have some dough with raisin in it. You let that dough rise. None of the raisins actually are moving through the dough (space) but they are all getting further apart from each other.

This analogy breaks down when you think of the surface of the loaf. There is no indication that there is any outside edge "surface" to the universe. It is suspected to either be infinite in size or it wraps around onto itself.

The Universe is NOT expanding into empty space. The Big Bang did not start in one spot and expand out but started everywhere, if it is infinite in size, and expands.

Getting your head around infinities and expansion is not easy and it is not intuitive because it isn't how we relate to things of the every day.

Middenrat
2009-Mar-03, 05:29 AM
DaveH, I don't think you can compare the experience of an entity residing in the distant galaxy with our own experience, because we are not contemporaries, i.e. we are not occupying the same time frame. That galaxy we glimpse at the limits of observation existed a long, long time ago and its environs would be consistent to itself.
Hmm, maybe in that galaxy the shape and size of the Universe, being much younger, would be discernible...?

Centaur
2009-Mar-03, 06:13 PM
We all know of the Big Bang Theory. We also know of the expansion of the universe as a result of the Big Bang. However, I have not heard just exactly where this Big Bang took place. If the universe is expanding in all directions from the point of the Big Bang we should be able to locate where that center point is. So, where is this point in the universer? Billions of lights years in the direction of Orion? Or maybe out in the direction towards Polaris? I'm sure I just missed this piece of information. Anyone know where the Big Bang took place in the Universe?

There is no center. The confusion arises from thinking of the Big Bang as an explosion of matter spreading out from a center. What is expanding is space, i.e. the coordinate system by which we measure distances. Another way of thinking of it is that a meter is continuously growing shorter. No matter where an observer is located in the universe, it appears as though he is near the center and most deep space objects seem to be moving away from him. The further away they are, the faster they appear to be moving away.

raptorthang
2009-Mar-03, 07:44 PM
Centaur gives a good account.

Physical space has no measurability without the variable of time. All references are variable as the universe expands.

Analogies like the balloon are all good as starting references...but all analogies can only take the concept so far. Whether it's the Big Bang, the Quantum and so on, what seals the deal, at least at this time, is controlled observation and experimentation...'Science'. We are physical beings that evolved in specific physical environments. Our physical senses are incapable of perceiving much of the reality around us. We can only ultimitaley 'know' because of the science. We can't know by closing our eyes and trying, no matter how hard, to picture variables and dimensions we don't experience.

speedfreek
2009-Mar-03, 07:48 PM
Apologies to anyone who has seen other versions of this explanation before, but I think it might help here.

The universe seems to be expanding metrically, where the metric that defines distance has been changing throughout time. What does that mean, exactly? Well, let's make a simple model to illustrate how a metric expansion seems to work.

Now to model an expanding space we need to assign coordinates within that space. For the moment, forget about any edges to that space, we don't need edges, we just need coordinates in order to measure the expansion of space. Galaxies come later, so for now just imagine a 3 dimensional grid. At each grid intersection we will assign a coordinate, a point, a dot. Let's say each intersection point is 1 meter apart.

Put yourself on a point somewhere in this space. Whatever axis you look along you see neighbouring points 1, 2, 3, 4, 5 etc meters away, receding off into the distance. Then we introduce some expansion. Let's say the space grows to 10 times its original size in 1 second! That seems fast perhaps, but this is just a model with easy numbers. The key thing to remember is that the grid expands with the space.

So, here we are, still sitting on our point (but it could have been any point) 1 second later. Now lets look along an axis. We see those neighbouring points are now 10, 20, 30, 40, 50 etc meters away. The space increased to 10 times its original size, and so did the distance between each intersection point on that grid.

Our nearest neighbouring point has receded from 1 to 10 meters in 1 second, so it has receded at 9 meters per second. The next point away has receded from 2 to 20 meters in 1 second, so that point receded at 18 meters per second. The fifth point has moved from 5 to 50 meters away in 1 second, so that one has receded at 45 meters per second. The further away you look, the faster a point will seem to have receded!

And the view would be the same, whatever viewpoint you choose in the grid! There is no "centre" of expansion, no origin point within that grid - the whole thing, the whole space has expanded from something where the spaces between things were really small to something where the spaces between things are much larger. The expansion of that space has carried matter and energy along for the ride.

Remember I said the grid of points receded off into the distance.. well a point that was initially 33,000,000 meters away will have moved away to 330,000,000 meters in 1 one second, meaning that it has receded at 300,000,000 meters per second - the speed of light! Any point initially more distant than 33,000,000 meters away from another point will have receded from that point faster than the speed of light. That is the distance were an object recedes at light speed in this "little" model of expansion. If you look at a point that has receded at the speed of light, then from that point, the point you are on has receded at the speed of light. But no object would be moving through space faster than light, no photon would ever overtake another photon, it all just gets carried along by the cosmic flow.

Now I know this is a very simple model, dealing with a simple 10 times expansion in 1 second. This might seem very different from a universe where the rate of expansion was slowing from immense speed and then starting to accelerate, but if you start your grid very small and apply different rates of expansion to that grid, incrementally, over different rates of time, to simulate slowing it down and then speeding it up, when you look at the end result it is essentially the same. (Whenever there is a change in the rate of expansion, it is the rate of expansion for the whole grid that changes).

You might be asking how useful this model actually is. Well you can substitute different distance measures and time-scales if you like but the principle remains. If you sprinkle galaxies throughout the grid and then expand that grid such that the galaxies move with the expansion, you would find that galaxies interact gravitationally with their near neighbours. The further apart galaxies are when they form, the less the gravitational attraction between them. If they are less than a certain distance apart, the galaxies will move towards each other and cluster together, but if there is enough distance they will be moved apart by the expansion of the universe.

Galaxies at the edge of clusters might have some attraction to their neigbouring clusters, but that is countered by the gravity of the closer galaxies in their own cluster. Thus, the edges of the clusters seem to stretch out, "filament like", towards others in a manner reminiscent of the spiders web structures of the SDSS survey.

We end up with clusters of gravitationally-bound galaxies and increasing distance between the centres of those clusters, in a universe where there is no "origin point" or centre of expansion. The whole thing was the origin point and we have no way of knowing how much larger than our observable part of it the whole thing is. We don't even know if it has an edge, and it doesn't actually need one, mathematically. It is not quite as simple as saying "if it has an overall shape, it must have a centre", unfortunately.

Gandalf223
2009-Mar-03, 08:13 PM
Prior to the BB (big bang) there was no universe. A corollary is that there was no frame of reference to measure the location of the pre-BB singularity or anything else.

More importantly, there is no convincing evidence that the physics of our universe were applicable before the BB. Without the same rules (if you will) there is no way to rationally assign any qualities to the pre-BB whatever-it-was. It need not have had density, size or a location, because those qualities all require a frame of reference that did not exist before the BB.

Also, without the rules we live by, there is no reason to assume that the speed of light, c, was the speed limit. In fact, there was no "speed of light" before the BB, because there was no light, no photons, no nothin' that we can define. So the initial expansion of the "protomatter" of the BB could just as well have gone much faster than c, and all of our known universe might have just winked into existence at some already unimaginably huge size.

nauthiz
2009-Mar-03, 09:02 PM
Prior to the BB (big bang) there was no universe.

More specifically, prior to the big bang there was only wild speculation. ;)

phunk
2009-Mar-03, 09:47 PM
Welcome to BAUT DaveH,

According to the Standard Big Bang Theory, our universe started out as a very small (theorectically, infinitely small) point, from which the BB started. When it started, spacetime also came into being and started to rapidly expand. Like the expansion of a ballon (as stutefish mentioned), whereby the surface of the ballon is the edge of the universe. Therefore, since everything was initially together, the center is everywhere.

You're thinking about it wrong. The surface of the balloon isn't an analogy for the edge of the universe, it's a 2d analogy for the entire universe. The space outside and inside that surface isn't part of the universe at all. That's why it can be said that there is no center, where would the center of a 2d surface be if it has no edges?

steve000
2009-Mar-03, 11:29 PM
The surface of the balloon isn't an analogy for the edge of the universe, it's a 2d analogy for the entire universe

I think that's what was meant - probably just worded differently.

DaveH
2009-Mar-04, 11:26 PM
I am getting a little closer to understanding why I don't get it. Thanks Speedfreek. We can place the BB in time and say that space before the BB didn't exist. From what I understand is that we cannot measure the size of space just the fact that it is expanding in all dimensions at rates that depend on how far you look. I can almost grasp that idea; howerver, no way to determine where you are in space is just not within my ability to understand. Probably why I am not a mathematician/physicist/cosmologist.

slang
2009-Mar-05, 12:20 AM
I can almost grasp that idea; howerver, no way to determine where you are in space is just not within my ability to understand. Probably why I am not a mathematician/physicist/cosmologist.

I know how you feel, and I think many others can sympathize too. It's difficult to "turn off" the understanding of gravity and time that have shaped your way of thinking from birth. Keep reading, soon you'll start to get a sense of in which situations you need to turn off 'intuition'. It's said that it's easier to understand when you get the maths, but I cant attest to that :)

speedfreek
2009-Mar-05, 01:33 AM
I can almost grasp that idea; howerver, no way to determine where you are in space is just not within my ability to understand.

Imagine that you are the only intelligent tree on a very large smooth planet that is covered by trees. The planet rotates once every time it orbits its sun and you happen to be right in the centre of the daylight side, so the sun is always directly above you (maybe that is why you are the intelligent one!). You can see other trees in all directions, but only as far as the horizon. You cannot communicate with other trees, you can only see them. You cannot move, of course.

How do you know where you are on the planet? You cannot move, you cannot measure the planet. Everywhere looks pretty much like everywhere else, there are no landmarks to fix your position with. The horizon looks flat to you (because the planet is so large and you aren't very tall it is hard to see any curvature). The sky never changes.

What could you work out about your position relative to the other trees? Would you be able to work out that you were on a planet? Would you be able to work out where you were on that planet? Would you be able to work out that the planet orbits a star?

We are in a vaguely similar position regarding how much we can know about the universe and our place in it.

zhamid
2009-Mar-06, 04:29 AM
If it were an explosion *in* space then there would be a location where the explosion happened (x,y,z coordinates). However, big bang started the space. The question "where in this space did big bang took place" therefore doesn't make sense.

But I suppose if you could find the centre of the universe then you could (may be) say that this is (sort of, kind of) where the universe started expanding from, assuming it is expanding equally in all directions. But you can't do tht because the visible universe is a subset of the overall universe (may be a tiny subset, who knows). You are at the centre of the visible universe, but we have no idea what the boundary of the total universe is (and we'll never know, if the theory of relativity holds), so we can never find out what the centre of the universe is.

WaxRubiks
2009-Mar-06, 07:39 AM
I think that's what was meant - probably just worded differently.


a lot of people don't understand the balloon analogy.


It took me a while to understand(or have some grasp of it anyway) the hypersphere(3-sphere) idea.

rommel543
2009-Mar-06, 05:28 PM
The best way I had it explained to me was by taking a rubber band and writing my name on it. They galaxies, stars, etc is the ink and space is the rubber band. You then stretch the rubber band and you can then begin to see spaces between the ink particles. The more you stretch, the more you see. The particles themselves aren't moving, it's the rubbber band being stretched.

Although I like speedfreek's indepth explanation, it clarifies a lot of the distance issues.

Arneb
2009-Mar-06, 06:23 PM
DaveH, welcome to BAUT. You already got excellent answers, so I'll just point you to one of our hosts' podcast series, Astronomy Cast (http://www.astronomycast.com/). You will learn all about it while listening to a very, very good show. The entries under "Cosmology" (http://www.astronomycast.com/category/astronomy/cosmology/) contain everything you want to know (like "What is the Universe exanding into"; "What is the Shape of the Universe"; "Where is the Centre of the Universe?")

mugaliens
2009-Mar-07, 04:54 PM
Exactly, Frog - it's not a 3D depiction, but a 2D (only the surface of the balloon) depiction of expansion.

nutant gene 71
2009-Mar-07, 06:42 PM
There is no rule that the universe should make sense to what is intuitive for humans. Remember that 'making sense' and 'intuition' are limitations of our brain, which from a very young age is being trained to deal with human scale reality, not with the vagaries of cosmic reality (or rather the scientific theories that describe it).
With all due respect Slang, the idea that the universe is beyond human reason or intuition limitations of the human brain defeats the purpose of the argument. Why bother answering at all? It has to make sense, or else it defaults to mystical magic, which is a priori unacceptable to reasonable beings. Otherwise, the answer is Sam5's: "Nobody knows."

Spaceman Spiff
2009-Mar-07, 07:56 PM
With all due respect Slang, the idea that the universe is beyond human reason or intuition limitations of the human brain defeats the purpose of the argument. Why bother answering at all? It has to make sense, or else it defaults to mystical magic, which is a priori unacceptable to reasonable beings. Otherwise, the answer is Sam5's: "Nobody knows."

Hmmm....I am not sure I follow your argument. Our scientific models are useful when they unify and explain our observations of the universe. Does Quantum Mechanics make sense to you? Despite what you might read in the popular literature, no one knows how to "make sense" of the quantum world, and yet our models are amazingly predictive. How about the invariant nature of 4-D space-time, while space and time are each coordinate dependent properties of the universe? I am not saying that our "making sense" of these are forever out of our grasp, but that despite our lack of intuition (or experience) in these matters we have two wonderfully useful models of nature in Quantum Theory and the General Theory of Relativity.

Now if you meant that our models must be logical, internally self-consistent and externally consistent with what else we know about nature, that the universe kicks back when we kick it, and/or are otherwise arguing against nonsense such as "What the bleep do we know? (http://en.wikipedia.org/wiki/What_the_Bleep_Do_We_Know)", then I'm with you.

Jeff Root
2009-Mar-07, 08:57 PM
There is no rule that the universe should make sense to what is
intuitive for humans. Remember that 'making sense' and 'intuition'
are limitations of our brain, which from a very young age is being
trained to deal with human scale reality, not with the vagaries of
cosmic reality (or rather the scientific theories that describe it).
With all due respect Slang, the idea that the universe is beyond
human reason or intuition limitations of the human brain defeats
the purpose of the argument. Why bother answering at all?
It has to make sense, or else it defaults to mystical magic,
which is a priori unacceptable to reasonable beings.
Otherwise, the answer is Sam5's: "Nobody knows."
You misunderstood what slang meant. He was saying that
people get intuitive ideas of how things work which quite often
are wrong. The correct ideas may be counterintuitive, which is
to say they don't 'make sense'.

-- Jeff, in Minneapolis

slang
2009-Mar-07, 11:20 PM
With all due respect Slang, the idea that the universe is beyond human reason or intuition limitations of the human brain defeats the purpose of the argument. Why bother answering at all? It has to make sense, or else it defaults to mystical magic, which is a priori unacceptable to reasonable beings. Otherwise, the answer is Sam5's: "Nobody knows."

You misunderstood my post, I think, and you took away the context of what I quoted, not to mention your adding of 'human reason', which I didn't say. Spaceman Spiff and Jeff Root have it right, that is exactly what I meant, thanks guys. I agree with what you mean in your post, nutant gene 71, it just has no connection to what I meant.

My response was specifically to the remark that "expansion makes no sense", intuitively. Expansion is a bit of a hurdle to overcome, witness the many threads explaining the dough or balloon analogies. That's understandable, our intuition builds upon what we experience in life. And there's little that trains the mind to prepare it for thinking about expansion.

Of course, once you 'get it', it's not so strange as it seemed before. Same with relativity and space-time and quantum physics (I'm not claiming I 'get those'..). Human reason will get past human intuition, if you let it. It's something that's on my mind a lot, but probably too much off topic here. I'm not prepared to put it in words anyway. :)

ETA: on further reflection, I think my short response to DaveH may have been taken as insulting, and I apologize if that was the case. I certainly didn't mean it that way, in fact I meant it to be encouraging, to keep working on improving reason, to overcome intuition.

WaxRubiks
2009-Mar-08, 12:35 AM
there's nothing wrong with intuition; it just needs a little guidance.

I worry that if people keep banging on about "it being counter-intuitive", then that sort of might become a self fulfilling prophecy.

What is counter intuitive to some may not be to others.

nutant gene 71
2009-Mar-08, 04:47 PM
So what I am hearing from this community is that everywhere/anywhere in the universe is the apparent center. This makes no sense no matter how many dimensions you conjure up. In a galaxy 13 billion light years away from us; an entity residing on a planet orbiting a star looks out into the night sky and sees other galaxies 13 billion light years away no matter where it looks is very difficult to conceive of, but this is what you all are saying. I think I am getting the Dark Energy/Matter explanation of why gravity doesn't explain the movements of galaxies and the expansion of the universe. Just make something up to cover our ignorance. It's almost mystical in nature. A spiritual entity ruling the universe makes about as much sense. Can't someone just say "we don't know why the center appears to be anywhere"
Very valid point DaveH, that if you are located in a galaxy at 13 billion light years away and look into the night sky, if space expansion and the Big Bang are real, one would expect (intuitively ;)) greater density of observable galaxies in one direction versus another. However, this is not what you would actually see. You would still see the same galaxy densities as seen from our Milky Way. It has to do with time and the dynamics of expansion, and how these are observed by us. Let's see if this explanation helps lift our 'ignorance'. :think:

Where you are now is the center of your 'observable' universe in the present time. So no matter in what direction you look, you are looking into a distant part of the universe that is backwards in time. As far as we can see (because it takes time for light to reach us a c), we are always looking backwards in time as we look out in space. The furthest reaches of our astronomical instruments is now about 13.5 billion years, but assuming we could look all the way to 13.7 byn years we would be looking from our present time into the beginning of time, or Time Zero. If the Big Bang is true, then at that point of zero time everything started expanding, first super-luminally during inflation and then sub-luminally since then into the present, which means you inhabit a giant universal sphere of 'visible time' of which you are at its 'observational' center, and the 13.7 bly edges are its observational Time Zero. This is true for everyone in the universe no matter where they are positioned within it. If you were positioned at any other galaxy today, you would still see the same distribution of CMB or galaxy densities as we do. This is because even if you are at what we see as the 'edge' 13.7 bly away, they over there still see themselves as the 'observational center' in present time, and Zero Time for them is still 13.7 billion light years away. That Zero Time region, which is the sphere of our observable universe, its outer limits of observation, is the same for everyone within it.

There is one more thing that tends to be confusing for people, why they have trouble with the "expanding raisin bread" illustration of BBT. In taking the giant universal observable bubble of time, with its observational center as present and 13.7 bly edge as original time zero, and then transposing that onto a physical universe, we tend to forget that we never see the 'present' for any other part of reality except our own; for all out there, it is always backwards in time towards time zero (with distance). But for other residents far from here, we are backwards in time for them, and they are the present time center for themselves; so for them they are the observational center of the universe. In effect, the raisin bread will never find itself (observationally) pushing against the aluminum pan because anyone within it can never be at Time Zero; we are all universally always at 'present time center' in all we see. So for every observer there is only present time center location no matter where you are in the 45 bly of existing space (http://www.newscientist.com/article/mg20126921.900-dark-flow-proof-of-another-universe.html?full=true), of which any one of us anywhere can only see the 13.7 bly line-of-sight radius. So unless you can travel through time like Dr. Who in his TARDIS (http://en.wikipedia.org/wiki/TARDIS), you can never travel to another part of the universe in present time because of light c observational limitations, and therefore you can never be at Time Zero 13.7 bly away. That TZ region of BBT space is ALWAYS 13.7 bly away for you no matter where you are. No matter where you go, there you are! :D

Here is a good paper that may clarify it further: http://arxiv.org/pdf/astro-ph/0310808v2

[There should be a caveat here, that all these explanations make sense only if the BBT and Doppler-like expanding space theories are right. If for some reason we were to discover distant light redshift is from some other non-Doppler causes (space static), then the whole exercise of understanding BBT becomes a clever parlor trick discussion, but not really what it's all about. Dark matter, for example, implies greater deep space gravity, which itself implies line-of-sight tunnel for photons traveling millions of light years to be gravitationally redshifted within that line-of-sight tunnel by the time is gets to us: the dark matter tugging on it within that tunnel at about the Hubble constant, which approximates Einstein's cosmic constant, which all fits the BBT scenario. But BBT does not have to be true of necessity, though all parts fit conceptually, if dark matter exists, IMO.]


OTOH, thanks to all who replied to my misunderstanding (http://www.bautforum.com/space-astronomy-questions-answers/84823-location-big-bang-2.html#post1449912) of Slang's post (above), I get it now. :)