Big Bang/expansion question

If you were to keep traveling forever, I think the universe would just look more and more empty because everything else will have kept moving away from you. So even though you'd still be nowhere near an 'edge' you might as well be looking at nothing because the rest of the universe would just seem to vanish. - Zor Prime

That makes some sense. But right now, at this point in time, there must be a planet that is the furthest. We measure objects that are one, two, one hundred, one thousand etc. light years away from Earth.
Would not the object (if we could see that far) that is millions or billions of light years away be the furthest? Yes, I know Earth isn't the center of the universe. But if we could determine the line of trajectory several galaxies are heading and take the 180 degree azimuth from that direction, we could indeed determine a relative point from which everything started to expand?

Which point on the surface of the Earth is farthest from your house? If you go there, do you reach the edge of the Earth?

There are lots and lots of theories and interpretations when it comes to your question. The most conservative one has been mentioned alread: No you won't look out into 'nothingness' when you are at the edge. Because there is no edge. None at all. And it's still finite. That is because we are four dimensional. But according to the various string theories, there are at least 10 dimensions. There is some mathematical evidence that there are 26.

Want to get a little mind fucked? Look here.

The most logical and elegant for me is the Branes Theory (there is more than one of course). It explains stuff like the Big Bang, 'overspace' and so on pretty neatly IMHO. Yet of course when it comes to these things, one theory is as good as the next. There is no part of science that comes closer to religious belief rather than hard evidence. Basically it's religion for supernerds and the implications and possibilities can sound like a holy book rather than a Science article. Especially since the available proof is basically the same...

I'm sorry, but this bugs me.

"This unknowable fact has been revelaed to me; I now know it beyond all worldly doubt."

"This is something we haven't figured out yet; there are several fascinating theories, and I'm not sure which one is correct."

The only thing those two stances have in common is that the issue in question currently can't be resolved by empirical evidence. In all other respects, they are as different as they could be.

Doesn't apply really. No matter where I am on Earth, if I look 90 degrees in relation to the Earth's surface I see stars.
From Earth's perspective, we see (if all galaxies are spreading apart) some that are further and some that are closer, all moving outward at a trajectory from a central point.
If they weren't moving from a central point, they wouldn't be moving in a straight line , they would be drifting around willy-nilly. Thus depending on their positions
and "order of march" some galaxies must be on the outside, if the universe is expanding. The only way the universe would look the same is if the universe were fixed and eternal,
but we know this isn't true. We can measure galaxies moving , but we can't prove or measure any dimensions other than three.
In other words if a galaxy is moving in a straight line it must be moving toward something empty like space/nothingness. A galaxy can't move through something that's already
occupying that same space. Thus if you were in an outside galaxy things must look different when looking in one direction, 90 degrees from what is behind you or to the side.
Maybe it's empty, maybe some other dimension, but it's still different.

There's a Bugs Bunny short, in which he throws a baseball so hard and far that he ends up turning around to catch it. Did the ball reach the edge of the Earth when it hit his glove?

That's the point, it does apply. If you manage to look 90 degrees away from everything else in the universe (don't strain your neck though), you'll look at borders, such as Planck's quantum limit.

Forget it. I still can't wrap my mind around anything other than an expanding sphere in three dimensions. X part of that sphere will always be further away from center than the others, to the point where X is the outermost and will be the outermost unless Y is moving faster and ends up further away. If Y can't overtake X, X will be the furthest out. If the sphere is moving into some substance other than the sphere (and indeed what the sphere is expanding into must be different or it would already be part of that sphere) then the surroundings of X will be different than Y, at least in one direction/angle.

That's all my primitive brain-stem can visualize, but thanks everyone for trying to explain it.

Nobody can wrap their heads around it. They can just point at the math and say that's it. Until the next guy with a better equation comes along.

@oldfella1962

Let me try giving you a different picture.

Imagine that reality before the Big Bang was a big flat sheet of paper. It has an extent in the (let's say) x and y directions. But no z axis!


Then the Big Bang happens...


There's this big disturbance in reality. And everywhere the disturbance propagates, it's adding a z dimension to reality.


Eventually, this disturbance has created a very large region where there are x, y, and z axes to reality. Space has been created where there was none before.


It's important to remember that the z-axis only exists INSIDE the disturbed region. It makes no sense to say what's above it nor what space is "outside" this region...there is no space outside the region! There can't be space where there aren't x,y, AND z axes!

There is no space where the universe hasn't expanded yet - so what would that look like? If you happened to be located further out from other planets (there is a physical distance between planets/galaxies we can measure, thus they are positioned at different locations) and looked in this direction what would we see? Nothing? Nothing exists there yet - so that nothing would look the same as the stars/galaxies that already exist and that we can plainly see?

@oldfella1962 - What does non-space look like? I'm not even sure that's a meaningful question.

Although we sometimes say "outside the universe" when referring to what may exist apart from the visible universe, there ISN'T (to the best of our knowledge) an outside. The outside of any X is a geometric space that surrounds X. But if there is no space apart from X, there is no outside. "Where the universe hasn't reached yet" assumes there's a space that the universe is filling up. There's not. The expansion of the universe is what is CREATING the space.

Your question about what you'll see looking out past the edge is meaningless because you won't (CAN'T!) find an edge. There is no region of space where you can put the visible universe behind you, and see nothing but empty space in front of you. It doesn't matter where you point the telescope: there's no area of the visible universe that's empty, devoid of galaxies, waiting to be filled.

This is what it means to say that space is curved. You can't picture the curvature, but you know it must be so because you can't find an edge despite the universe being a finite size. How else can something be a finite size and have no boundary?

To go back to the old analogy: imagine you're an ant crawling on a globe. To you, the world is only two dimensional: the surface of the globe. You're so small compared to it, that the surface seems flat to you. But if you walk around enough, you'll find that the globe is (1) a finite size, (2) that it has no edge, and (3) that you can set off in one direction and return to where you started without ever turning around.

So, when you look very, very deep into space, what do you see? You see another part of the universe--perhaps even the part "behind" you--as it was billions of years ago. There is no direction you can look that will show you "out." Every light path in the universe stays in the universe.

You certainly can't look beyond an edge, but in some ways, you can see that the edges are there. One such edge ist the speed of light, which is why you only "see" other parts of the universe in their past states their present state is not (yet) part of (your) universe; another is Planck's quantum limit, which is why you only "see" distinct places and impulses beyond a certain size -- their (uncollapsed) state is also not (yet) part of your universe. (These are not necessarily directly connected to expansion, just talking about non-spatial limits of the universe in general.) While you won't find an edge directly in any spatial direction, the idea of curved space, leading you back to where you started out from, could be said to give you an idea of "edging along" the border of your world.

I give up! I can only imagine the universe/galaxies expanding outward in all directions in a straight line. Since there's nothing to slow it down (indeed, the expansion is speeding up)
and there is only infinite nothingness offering no resistance it would only get bigger but remain a general three dimensional sphere. I can't visualize it taking on any other shape.
So you would see things behind you and to the side but not in front, because there's nothing there. The universe will be to that point as it expands, but it's not there yet.
And let's say the universe is curved - at what point will it start to curve? So far everything is moving outward and hasn't varied it's trajectory yet.
Sorry, that's as far as my abstract reasoning goes. I can only visualize in three dimensions and the simple intuitive physics I can see and measure.
Talk amongst yourselves because I'll never get it.

What's your trouble with imagining an expanding balloon, and seeing that as its volume grows, so does its surface, although the surface doesn't have borders?

I think it's the extra dimension(s) tripping him up. It is a bit hard to wrap your noggin around.

Ummm.......because an expanding balloon has a border? I have seen a few expanding balloons, but not another dimension. Also I don't need much abstract reasoning or math background to
visualize a real balloon expanding, no matter how big it gets what's not "balloon" will look different than what is "balloon."

What about the space defined by those additional dimensions?
Does it have an edge, or is it surrounded by still more dimensions?

I'm cool with only three - they serve me well. Okay The Fifth Dimension had their moments, but that's about it.

You're missing the point of the analogy.

If the universe was two-dimensional, it would be like the surface of that balloon. It's expanding, but there's no edge. To a two-dimensional creature on the surface of the balloon, the "universe" is finite but with no boundary. He can walk everywhere on the balloon's surface but find no edge. He can even set off in one direction and return to where he started from the other. His ONLY conclusion can be: the universe is curved in a way he can't sense.

The balloon analogy shows you what a two-dimensional universe curved into a third dimension looks like.

Our universe is a three-dimensional one curved into a fourth dimension (or perhaps even more).

I can't draw you a picture of what it looks like. I can't show you a four-dimensional object.

But I can DESCRIBE it.

You could (in principle) travel anywhere in our three-dimensional universe and not find an edge, and, if you traveled long enough (perhaps laying down breadcrumbs as you went), you would eventually realize that the space contained in the universe is finite.

So, you're left with a (seeming) contradiction: no matter which way you go, you don't get "out." If you go far enough "west," you wind up in the "east." If you go far enough "up," you wind up "down." You have to conclude that the universe is curved in a way that means there is no edge.

Just like the ant crawling on the globe.

The balloon is an analogy. You CAN'T see another dimension. The balloon is just a three-dimensional model of something that's actually happening in more than three dimensions.

If the universe were like a balloon, and there was not-balloon outside of it, you would (in principle) be able to travel to a point outside of the universe. You could look back and see the entire universe behind you, and look forward and see nothing but empty space.

But that's now how it is. You will not find such a place, because such a place does not exist.

"So, you're left with a (seeming) contradiction: no matter which way you go, you don't get "out." If you go far enough "west," you wind up in the "east." If you go far enough "up," you wind up "down." You have to conclude that the universe is curved in a way that means there is no edge."- Paladin

Not to burst your bubble (no pun intended) but this could be speculation and theory. Obviously no way to prove this in our lifetimes, but we all could be way, way off with what the truth may really be.
I think in 1,000 years scientists will laugh at what we used to think.

Sure, it could be.

Let's assume it is and your simpler model is accurate: the universe is just growing in the middle of an already existing space.

We know we're not on or near the edge, right? We can't look in one direction and see nothing. So, we must be somewhere in the interior.

So, what should we see when we look around? When we're looking toward the center, we should see a higher concentration of galaxies. When we're looking towards the nearest edge, we should see a lower concentration of galaxies.

Do we see that?

No. The density of galaxies is pretty uniform no matter how far we look.

And we can look pretty damned far. In fact, we can look so far away, we can see back almost to the beginning of the universe.

Maybe, maybe not. But if we don't develop new ideas today, there won't be any new ideas tomorrow.

UNLESS the universe is much, much, much older and bigger than we think, in which case we are not looking that far into it as we think. The universe is expanding faster as it gets bigger, right. Maybe the very outside part is moving so fast (almost at the speed of light) we'll never be able to see it (or the edge) from where we are. But from a planet in one of those further most galaxies it does indeed look
very, very different.

A tesseract is one way of trying to understand the idea of dimensions beyond that which we can directly observe. In this 3d projection of a 4d object, every edge is actually the same length.



http://en.wikipedia.org/wiki/Tesseract#Projections_to_2_dimensions

Based on how fast galaxies are moving away from one another, we certainly think we have a good handle on when the beginning was.

I don't think so. We can see objects that are almost as far back in time as we estimate the age of the universe. And, although they're moving very fast away from us, we don't see any that are moving faster.

I read that the universe is expanding faster the bigger it gets. Was that wrong?

No, you are not wrong. The universe's expansion does seem to be accelerating. The concept of "the cosmological constant"--a term Einstein erroneously introduced into his field equation of General Relativity--has even been revived as a mathematical way of describing the effect.

But that doesn't change what I said. If some galaxies were speeding away from us at or near light speed--and, believe it or not, it's actually possible for them to recede from us at greater than light speed [that's another topic]--we would see other galaxies receding almost as fast. But we don't.

This is a good point. Latest experimental data is that the overall curvature of space on a large scale is close to zero. That would imply that the kind of model being discussed here is not correct. (Although it does make mathematical sense, despite inability to "picture" it.)

It would also imply that the universe is "open" or unbounded.

It can be flat yet bounded...