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What Is The Universe Expanding Into?


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The universe is expanding. I get that...it's still on the move after the Big Bang. But what is the universe expanding into?

 

I've heard the analogies about the loaf of raisin bread in the oven, where the raisins (planets; galaxies) are in the bread and getting further apart as the bread bakes. But the bread as a whole is still expanding into the interior of the oven. The way I understand it, the interior of the oven is a finite place, and so I can say the bread is expanding into it.

 

What is the "it" that our universe is expanding into then? Is it a place? Is it a an expansion at the expense of nothingness, and if so, what is the nothingness made of?

 

If I look at the sky 10 billion years from now, I will see that the closest galaxy to ours has gotten further away from us. Where is it going to, and what is it displacing?    Mostly, and this is what I don't get...what would it be displacing?

 

I've wrestled with this for a long time and don't get much of what I've read about it. Can someone here explain it to me like I'm a nine year old, or recommend any books?

 

I hope this is the correct place to put this question.

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This is a good question.  I've actually never heard the analogy of raisins in a loaf of bread.  The analogy I used to give students was that of an expanding balloon, but this will pose the same difficulty for you, since much like the loaf of bread, balloons still expand into something else.  It might make it easier, though, if you imagine yourself as an ant living on the balloon.  The ant effectively lives in a two-dimensional world.  That world exists in a higher dimension, allowing it to curve.  And that curvature affects the ant's motion, e.g. as the balloon expands it takes longer to get from one point to another.  But as far as the ant is concerned there are only two dimensions.  While the balloon might be expanding in some higher dimension, the existence and nature of that dimension is immaterial to the ant.  Like all analogies, this one can of course is only intended to aid in understanding, and will break at some point.

 

If you are mathematically inclined, I might replace the balloon analogy with a higher-dimensional manifold, i.e. a curved surface with more than two dimensions.  In general relativity, space is described by one time coordinate, and three space coordinates.  The Einstein Equations describe the curvature of this space, and that curvature is governed by gravity.  In a universe with no matter, space is "flat," that is, it is described by the simple three-dimensional Cartesian coordinate system you might have seen in geometry or calculus (actually, the time coordinate makes it a Minkowski space rather than Cartesian).  In this space, distances between points can be readily computed by the Pythagorean Theorem.  But matter bends space, causing distances between points to be given by formulae other than the Pythagorean Theorem.  The solutions to the Einstein Equations are mathematical objects called metric tensors, and these give the distance between any two points in space.  Now, here's where the expansion of space comes in.  As space expands, the distance between any two points increases with time.  This is the sense in which space is "expanding," and why there is no reason to envision a higher dimension into which the space expands.

 

One important point here is that just the Big Bang causes space to expand, gravity has a sort of opposite effect.  The Andromeda Galaxy, which is nearest to our Milky Way, is close enough that the cosmological expansion effect is negligible; it is in fact moving towards us.  In 10 billion years it will have actually collided with our galaxy, rather than having receded due to cosmological expansion.

 

Apologies if my explanation was overly technical.  Fortunately BAA is more skilled than I at communicating the field of cosmology to general audiences, and I'm sure this thread will quickly catch his attention.

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It's expanding into the Hell that was created for people who ask "What is the universe expanding into?"

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Watch Cosmos and the inexplicable universe if you want REALLY simple explanations to your questions.

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Bhim and others will not care for what I'm about to say because it's unconventional, but it's true.  The universe is both expanding and contracting.  It contracts in regions of intense gravitational fields and expands outward from there.  Implosion.

Also, its expansion is something of an illusion created by the fact that light is red-shifted more and more the further it is away.

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Voice, light is red shifted because of the expansion. This is one of the great predictions of an expanding universe model. This is why the high energy light from the early universe can only be detected as markedly red shifted microwaves. The evidence is pretty clear that the overall universe is expanding.

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I call for Bhim, here, but I'll give it a shot. 

 

As I understand it, it's infinitely weirder than raisin bread...

 

The universe isn't expanding into anything, really. Because the universe isn't a thing like a balloon or bread, but matter distributed through the dimensions of space-time, which is what is itself, expanding. The "stuff" of the universe is almost all empty space, pure space-time. Matter exists as probabilistic waves of energy, in different states, and makes up a tiny fraction. Since the universe IS the space-time, there's no "something" for the universe to expand into. It's just expanding. 

 

On the whole, the universe and this vast matrix of space-time IS expanding, due to the tremendous amount of energy from its origins, as well as the energy contained in empty space (represented by the cosmological constant). So, actually, "nothing" contains a colossal amount of energy, that is driving the expansion of the universe. 

 

Locally, however, high enough concentrations of energy, in the form of mass or speed, can condense space-time, causing things like the orbits of planets around stars, or black holes, or Einstein Rings (the light is traveling from a source in a straight line across space-time, but it's the space-time itself that is curved around a massive object in between the observer and the source). Einstein rings are one of the proofs that Einstein was right about the nature of space-time and relativity.

 

WMAP survey!

 

Einstein Rings!

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Thank you all for the replies so far, and any to come. Some of you must have some very smart nine year olds where you are!

 

I got a little busy after I posted this, but I'll be back in a day or two to re-read everything and follow links.  

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I call for Bhim, here, but I'll give it a shot. 

 

As I understand it, it's infinitely weirder than raisin bread...

 

The universe isn't expanding into anything, really. Because the universe isn't a thing like a balloon or bread, but matter distributed through the dimensions of space-time, which is what is itself, expanding. The "stuff" of the universe is almost all empty space, pure space-time. Matter exists as probabilistic waves of energy, in different states, and makes up a tiny fraction. Since the universe IS the space-time, there's no "something" for the universe to expand into. It's just expanding. 

 

On the whole, the universe and this vast matrix of space-time IS expanding, due to the tremendous amount of energy from its origins, as well as the energy contained in empty space (represented by the cosmological constant). So, actually, "nothing" contains a colossal amount of energy, that is driving the expansion of the universe. 

 

Locally, however, high enough concentrations of energy, in the form of mass or speed, can condense space-time, causing things like the orbits of planets around stars, or black holes, or Einstein Rings (the light is traveling from a source in a straight line across space-time, but it's the space-time itself that is curved around a massive object in between the observer and the source). Einstein rings are one of the proofs that Einstein was right about the nature of space-time and relativity.

 

WMAP survey!

 

Einstein Rings!

 

Well...part of this is right.  It's true that the universe isn't expanding into anything, and that the universe's expansion comes from the Big Bang.  However, I would be remiss not to mention that quantum theory (i.e. "probabilistic waves") isn't relevant here, since GR covers the universe on a large scale where quantum phenomena play no role.  Indeed, the unification of quantum mechanics and GR is one of the great puzzles of physics that remains to be solved, but GR in its current state is a classical theory.  Also, I would point out that the universe, in theory, can exist without matter.  It's the matter that bends space, and as you say this is what causes the orbits of planets and all other gravitational phenomena.

 

Anyway, thanks for contributing to all this!

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I didn't think I'd be able to come back to Ex-C for a couple of days, but things didn't turn out that way, so here I am. I've heard  the balloon analogy too, but the balloon is expanding into the room that it is being blown up in, and that to me was just the same as the raisin bread one, but without the warm melted butter.

 

I went to my local library today and picked up a couple of books from the "juvenile" section about the universe. Maybe I should have done that in the first place. I had to thank the librarian for not chuckling at me (not that she would have), when I told her of my brilliant scheme to find a book on my level of understanding. There I was in my winter coat, looking a little gruff I imagine, 58 years old, and telling her I wanted to know what the universe is expanding into. From a children's book.

 

I'm hoping I can finally understand this. It's been bugging me for years, and it still is. The universe is expanding. To say that it's not expanding into anything seems preposterous. It has to be expanding into something!  Right?  Wendytwitch.gif

 

I'll find out. You'll see.  

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It's expanding into Cleveland. 

 

I suspected Cleveland at one time, but I drove through it once in the eighties, and the universe was already there. From what I could see, Cleveland was fully engulfed in the universe and it had been for some time.

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Am I wrong to assume that 'nothing' or a void creates no barrier?  Why couldn't it expand into the emptiness?  If it couldn't, then there would be something; something that blocks, right?

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Either the last or second to the last episode of the inexplicable universe explains what the expansion is doing and will eventually cause.

 

Just sayin'...

 

Can't say it enough.

 

Just watch it already!

 

:-)

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Am I wrong to assume that 'nothing' or a void creates no barrier?  Why couldn't it expand into the emptiness?  If it couldn't, then there would be something; something that blocks, right?

Is a void something? Is nothing nothing, or is it something? Didn't I bring this up in the OP?

 

Oh, and yes, you are wrong to assume.

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Either the last or second to the last episode of the inexplicable universe explains what the expansion is doing and will eventually cause.

 

Just sayin'...

 

Can't say it enough.

 

Just watch it already!

 

:-)

If it's on Netfix or Youtube, I will.

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Either the last or second to the last episode of the inexplicable universe explains what the expansion is doing and will eventually cause.

Just sayin'...

Can't say it enough.

Just watch it already!

:-)

 

If it's on Netfix or Youtube, I will.
It is! Cosmos AND Inexplicable are on Netflix!
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Am I wrong to assume that 'nothing' or a void creates no barrier?  Why couldn't it expand into the emptiness?  If it couldn't, then there would be something; something that blocks, right?

Is a void something? Is nothing nothing, or is it something? Didn't I bring this up in the OP?

 

Oh, and yes, you are wrong to assume.

 

 

Why does a void have to be something?  If there's nothing, why does nothing create a barrier? 

 

I think our minds want to put something into the nothing because the environment in which we live, there is always something, be it a gas or whatever.  Just because we can't fathom it given our limited perspective doesn't mean the edge of space has to parallel with our own limited experience within this environment as best I can tell. 

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The universe is expanding. I get that...it's still on the move after the Big Bang. But what is the universe expanding into?

     If I'm reading you're question correctly then it should be possible to rephrase your question as "What is outside the universe?"  Am I right?  A balloon has an inside filled with air and it expands into another volume, which in our case, is also filled with air.  So the balloon expands into the air around it.  The inside of the balloon is where you imagine we live and the outside is where you imagine we're expanding into with the balloon itself being the "edge" of the universe itself.  Am I understanding you correctly?

 

     If this is the case you've misunderstood the analogy.  We don't live inside the balloon.  We live on the balloon itself.  The actual "skin" of the balloon.  What you might say was the "edge" of the universe from above.  Nothing is inside the balloon (this is where wormholes could allow travel so you could avoid moving along the skin).  And outside the balloon?  Nothing is there either.  Or at least "undefined."  Because we can't go there.  It's not for us.  Perhaps if we move to another dimension but as it stands that's not some place we get to be.  The entirety of our universe lies on the skin of the balloon.  And it only gets to "stretch" as the balloon inflates from its initial burst of energy.

 

     So what are we stretching into?  It's not known.  Something.  Nothing.  We'd have to get outside ourselves to really know what's happening and that's not possible.  We can theorize but that's about it.  But we see our universe as everything that is.  So with that definition it's not possible that there's anything that is not our universe.  We can't be moving into anything as we're already there.  Our perspective only allows for so much.  From where we're at we're not expanding into anything.  The question is not meaningful in any way.  From another perspective this might change.

 

          mwc

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Ok Dude, 

 

I'll give this a shot.  (Thanks btw Bhim for the kind words.)

 

But I'll use this site... http://oneminuteastronomer.com/6949/where-is-the-center-of-the-universe/ ...to help me.

 

 

Balloon-Analogy.jpeg

 

I prefer the expanding balloon image to the raisin bread one.

As has already been explained earlier, we need to think of ourselves as living on the surface of the balloon.  This surface is a two dimensional (2D) representation of a 3D volume of space.  Visualizing that shouldn't really be a problem, because when we look at a photograph or a painting, we've no trouble 'seeing' that it's a flat, 2D image of 3D object.

 

sara_bookmark450.jpg114240651_cat_342943c.jpg

 

I needn't ask which one of the above is 2D and which is 3D, right?

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So, in the sequence above, we see a flat, 2D balloon expanding it's 2D SURFACE area.

But since we now know that this is just a symbolic representation of a 3D volume of space, what's this sequence is really showing is a 3D universe expanding it's 3D VOLUME. To those living in this volume (us!) it seems as if space itself is expanding.  The Big Bang isn't shown in the sequence, but if it were, it might be represented symbolically on a 2D page or screen by a 1-dimensional dot that 'balloons' outward, growing a 2D surface (actually a 3D volume of space) from zero (0) dimensions and expanding into... into... umm ...see below. 

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Ok, so our naive 3D logic would seem to tell us that any 3D object expanding in volume must be expanding into a larger 3D volume, that contains it.  The Dude's example of the expanding bread in the oven is a classic example of this thinking.  We're familiar with examples of this kind of thing in our everyday lives and it's natural for us to continue thinking in these terms, even about the entire universe.  

 

But that kind of thinking won't help us tackle this problem.

In fact, it just creates more problems.  Out next question (using this train of thought) will be... "So what volume of space does the oven fit into?"  Followed by... "And what volume of space does the kitchen fit into?"  Then... "And what volume of space does the house fit into?" And so on, ad infinitum.  We just get a headache and no real answers trying to figure things out like this.

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To be honest, I just don't know what the universe is expanding 'into'.

There!  I've said it!  I've fessed up not knowing the answer to the question. But I will go out on a limb and s-p-e-c-u-l-a-t-e.  Let's rewind to ancient times, when everyone was certain that the world was flat. *  Like the ants living on the surface of the balloon, everyone was ignorant of the Earth's true, 3 dimensional nature.  I suspect that we're currently in a similar situation, when it comes to understanding the true nature of the universe.  It could be that our 3D universe is expanding into a 'higher' 4 or 5-dimensional 'volume' that we are totally unaware and ignorant of.  Like the ancients, who's flat, 2D thinking couldn't help them imagine the true, 3D nature of the world - so we might be unable to imagine what the higher dimension our 3D universe sits in.

 

But that is. of course, just speculation on my part.

 

If it helps, go see 'Interstellar'.

At the climax of the film, the fully 3D hero occupies a 2D volume of space behind the bookshelf of his daughter's bedroom, even though from her p.o.v. there's no space at all behind the bookshelf.  It's just a solid wall.  I use this as an illustration of how objects we think are solid and 3D, (like a universe) when viewed from some kind of higher dimension, may well appear to be flat and 2D.

 

Think of the flat cut-out kitty stretching itself up and out of it's flat, 2D surface and becoming a fully 3D dimensional cat.

But do it as a 3D volume stretching into a 4D super-dimension.  And don't just do it for a cat - do it for the whole universe!

 

Brain-fry?  Me too.  Sorry 'bout that!  sad.png

 

That was my best shot, Dude.

 

Thanks,

 

BAA.

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*

Actually, Erastothenes establish that the Earth was sphere, over 200 years before the time of Jesus.  So not all the ancients thought the earth was flat - just most of them.  http://en.wikipedia.org/wiki/Eratosthenes 

 

 

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Even if you don't follow what BAA is saying here, go see 'Interstellar' anyway. Its an awesome ummm, uuuuh non-fiction sci-fi thriller!

 

That's the best way to describe it. Its very cool.

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A big thank you to everyone who answered me in this thread. I've read all of the answers at least twice, and some three times. I've followed the links, and I've watched Cosmos (actually, I already had), and the episodes of Inexplicable Universe that Fwee mentioned. I haven't seen Interstellar, but it's on my to do list.

Instead of quoting/answering everyone individually, here's my synopsis so far...

 

What I've gathered is that we don't know what the Universe is expanding into physically (i.e. point A to point B,) but we know that it is expanding.  Is it expanding in some other way than physically, then? That is, if I'm on the edge of the balloon, it's not that I can feel the wind in my hair as I move into some unknown or uncharted "place" that is "outside" of the Universe itself.

Is what makes it expand, or would I be wrong to say "seem to expand", is that matter/mass is actually bending space-time in such a way that it seems that the Universe is getting bigger because it takes longer for the light from other galaxies etc. to reach us, and it would take more time for us to travel to them than it would have yesterday?  This would only be possible if the mater in the Universe were getting...heavier, as it were.

 

Am I at least moving in the correct direction on this stuff?

 

Edit: Typos

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Ha-ha!!! This is cool! Science and cosmology have unleashed the beast within the dude!

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Ok Dude!  I can help you out here.

 

Firstly, a balloon has no edge for you to stand on. 

Like any sphere or ball or the planet Earth, a balloon has no edge and only one surface.  If you recall, I mentioned that the three balloon expansion sequence represented our 3-dimensional space in an purely symbolic, 2-dimensional way.  We don't live inside the balloon, we live on it's surface.  That's why the galaxies are drawn on the surface and not inside the balloon.  So a flea crawling on the surface of the 2D, cut-out kitty WILL come to an edge but a flea crawling thru the fur of the real, 3D cat WILL NEVER come to an edge.  In a similar way, an ant can walk endlessly around and around the surface of a ball without coming to an edge because the ball is a 3D object with just one surface.

 

Likewise, a yachtsman can sail endlessly around the Earth without ever falling off the edge of the world. 

To the ant, the yachtsman and the flea on the 3D cat, their journey never ends.  In a similar way, our 3D universe has no edge we can arrive at or fall off.  The so-called, 'edge of the universe' is a different thing altogether.  It's an observational edge, not a real and physical one.  It's the limit of how far we can see, not the physical boundary of the universe.  Ok?

 

Let's visit our yachtsman again.

If he's in mid-ocean and far away from land, there's an observational edge to his world.  This is his horizon.  The planet Earth doesn't come to an abrupt edge beyond his horizon, but goes right on, eventually forming a sphere.  So the curvature of the Earth sets an observational limit to how far he can see.  When it comes to our universe, our observational horizon isn't set by the curvature of space, but by the speed of light.

 

To understand how this works we need to know three things.

The speed of light, when the universe began and how much it's expanded by since it began.  We can measure all three things and the result of that calculation tells us that we can see no further than 46.5 billion light years.  Beyond that distance, the light from distant galaxies simply hasn't had enough time to reach us.  Even though we can't see any galaxies beyond this limit, we infer that they must exist there - beyond our observational horizon.  That's why the phrase the, 'edge of the universe' is so easily misunderstood. It doesn't refer to any kind of wall, edge, limit or physical boundary - it's just how far we can see.  You cool with that?

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So Dude, you might now ask yourself this question.

"How the **** do we know that the universe is expanding if we can't look at any kind of edge to see this expansion?"

Excellent question!.

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Here's how.

Look back at the three balloon sequence and check out the size of the galaxies. 

Q.  Are they getting bigger as the surface area of the balloon expands?

A.  No.  They're staying the same size, but the space between them is expanding and getting larger.

 

That's the key to unlocking this mystery!

You don't need to find an edge to see if the universe is expanding - you just need to measure the distance between any two points and see if that's changing over time.  Guess what?  This is exactly what astronomers see when they look far out, beyond our local group of galaxies.  The further they look, the faster galaxies appear to be moving away from each other.  This is the famous Red Shift. 

 

Ok, all the galaxies appear to be receding from us, but that's simply an optical effect.

If we could transport ourselves instantly 10 billion light years in any direction and look at the galaxies again, they'd still seem to be receding from us.  With every galactic cluster moving away from every other one, it doesn't matter where we go - everything in the universe will still appear to be moving away from us. 

 

So we know that the whole universe is expanding (as per the balloon sequence) by looking at the growing distance between the galaxies - not by finding any kind of edge.  Also, there's no need to suppose that the universe is getting heavier and this increasing mass is causing space to warp more and more.  In fact, astronomers have measured the shape of the universe very carefully and have found  no large-scale warping due to an increase of mass.  However, the 'shape' of the universe is another (related) subject, but we don't really need to address it to understand universal expansion.

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Anyway, does that help you out, Dude?

 

Thanks,

 

BAA.

 

 

 

 

 

 

 

 

 

 

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