What is the universe expanding into?
May 12, 2010 6:52 PM   Subscribe

What is the universe expanding into?

I'm not a scientist but I've always been interested in astronomy and cosmology. Recently it occurred to me that if it is true that space is expanding as a result of the big bang -- it has to be expanding into something "space-like." Otherwise, it wouldn't be able to expand.

Or am I missing something? Is it that space is an emergent quality of the universe, or are there higher dimensions at work?

I probably don't even know how to ask this question properly, as must be obvious. But can someone give me a good answer? Because I can't find it anywhere. And it makes my brain hurt.
posted by Guy_Inamonkeysuit to Science & Nature (27 answers total) 17 users marked this as a favorite
There's a wikipedia section on it, but it makes my brain hurt
posted by ghharr at 6:55 PM on May 12, 2010

As far as we know, it's just expanding. It's not expanding anything, it's not even expanding into nothing. It's just expanding.
posted by kirkaracha at 7:00 PM on May 12, 2010 [2 favorites]

See Into what space is the universe expanding?. Roughly, space is a relative quality and the distances between objects increasing is what is meant by expansion.
posted by Paragon at 7:00 PM on May 12, 2010 [1 favorite]

Imagine an infinite rubber sheet, stretching as far as the eye can see.

Now take out your trusty sharpie and make two little spots on it, about a foot apart. Or a stick figure adam and eve, if you prefer.

Now imagine the giant spaghetti monster reaches down with his infinite invisible noodly appendages and grabs a lot of points on the rubber sheet and stretches them apart. Observe! The dots you drew are moving apart from each other, because the space itself in which they exist is expanding.

There ya go - you have an infinite universe in which space is expanding. There's nothing 'there' for it to expand into, but it's expanding just the same.

If that still doesn't make sense, just imagine a finite rubber sheet with a couple sharpie dots on it, then imagine stretching it in both directions at once. Once you've got that image, just let the rubber sheet grow, until the edges are so far away it looks infinite to you. Ta daaa!
posted by Salvor Hardin at 7:14 PM on May 12, 2010 [11 favorites]

The stuff we can see is expanding, not the box it is contained in. Roughly.

Also, since we are limited by the speed of light, we can only see stuff that's a certain distance away. There could be a Norse God charging at us on the Flying Spaghetti Monster, we just can't see it yet.

(Pony express analogy: you live in a world where the only way to get information is on the Pony Express. Your aunt lives in San Antonio, and that is one year away from you via Pony Express. Your cousin had her baby, and your aunt dispatched a post card immediately. You recieve that post card today. Today is the baby's first birthday.

The pony express is the speed of light. We can't get information any faster. The further away something is, the longer it takes for us to see it and the older the information is. If the sun blew up RIGHT NOW, we wouldn't know about it for 8 minutes.)
posted by gjc at 7:16 PM on May 12, 2010

The universe is infinite. It started out that way. It's expanding everywhere, at once. It is not expanding into something else. It is space itself that is expanding. The expansion is happening at the same rate everywhere, too, I believe.
posted by alms at 7:23 PM on May 12, 2010

The universe is infinite.

I don't think there is a consensus about whether this is true.
posted by rancidchickn at 8:25 PM on May 12, 2010 [2 favorites]

The issue with answering this question is that the human brain can't comprehend anything that isn't dictated by space and time. Beyond the end of the universe, there isn't nothing because that indicates an emptyness in which you could place things; there isn't even time and space and that is the concept that is tough to get your head around. As for the universe, it is essentially space and time that are expanding and we can only tag along for the ride.

Questions can also be raised about whether the universe will continue expanding forever, reach a point and come back for a big crunch, or oscillate between expanding and contracting. But that's a totally different (and often misunderstood) topic entirely.
posted by iwillcatchthebird at 1:16 AM on May 13, 2010 [2 favorites]

It isn't expanding into anything. You're thinking in Euclidean terms, and space is non-Euclidean.
posted by Chocolate Pickle at 1:30 AM on May 13, 2010

Cosmology is usually done with Einstein's Theory of General Relativity. That theory basically doesn't answer the question. It might be that another theory comes along that can (as an example, brane cosmology has a 'bulk' in which the universe as a whole exists). It's not needed for GR to say what might be somehow outside the universe in order for it to give good answers, even if it gives us headaches to think about it.

On whether it's infinite - that's not determined. I can't see how it could be either, you can only really show if it looks finite, and currently it doesn't. Which isn't the same thing as saying it looks infinite, just as examining a small piece of my office floor doesn't tell you the size of my office. It certainly looks flat, but again that doesn't tell you it is flat in just the same way looking at the small piece of my office floor doesn't tell you that the Earth is flat.

The fact that space looks flat shows that on large scales it's perfectly reasonable to think in Euclidean terms too - the question of whether there's something somehow outside the universe isn't really one of whether the geometry is Euclidean or not. I think it's just as valid a question for non-Euclidean geometries as it is Euclidean.

In short, we don't know.
posted by edd at 2:29 AM on May 13, 2010 [1 favorite]

I'm certainly no expert, but as I understand it, it's expanding into absolutely nothing.

Not nothing as in a vacuum, or empty space. Even the depths of interstellar space is something, it has space and time and dimensions.

If you can get your head round it, it's expanding into.... nothing.
posted by derbs at 3:09 AM on May 13, 2010

The short, brain-hurting answer is no, it doesn't have to be expanding into something and it probably isn't.

To stop your brain from hurting, just accept the fact the world in which our brains evolved is incredibly different from the rest of the universe, making it very hard to impossible to truly comprehend.
posted by Midnight Rambler at 4:49 AM on May 13, 2010

A related interesting question.
posted by Prawn at 6:01 AM on May 13, 2010

Pretend for a moment that instead of expanding, the universe is blue, and it's gradually turning more blue. The fact that it's turning blue says nothing at all about what's outside the universe; there doesn't even have to be anything 'outside'. It's just turning blue, is all. Now pretend "turning blue" means "getting bigger."

Thinking of it as "expanding" or "stretching" or "growing" is misleading, because that automatically conjures images of some space that it's expanding into. Think of it instead as just "containing more space than it used to".

Another way to envision it: the universe is graph paper; it's got a certain number of squares in it. Each square represents one square meter of space, say. Gradually, over time, lines get added to the paper, so there are more squares, so there's more square meters on the paper, so it's "bigger". (This one's still kind of misleading, because you can still picture some space outside the graph paper, and could imagine someone holding a ruler up to the paper to measure the squares... so the tricky bit to remember with this analogy is that the rules which apply to the graph paper (one square = one meter) don't apply to the ruler; the concept of distance and measurement don't carry over from one to the other.)
posted by ook at 6:04 AM on May 13, 2010 [2 favorites]

Response by poster: Great answers, everyone -- but I'm damned if I can mark one as "best." This is like string theory, which I also struggle with. It seems reasonable to me that as part of the universe we ought to be able to understand it. If (hypothesized) higher dimensions are sub-atomic, and "curl around" particles, and if particles are constantly popping into existence in space, it may follow that the universe requires these higher dimensions and a constant rate of particle "creation" for what we call "expansion."

I discovered this vid on YouTube last night and found it helpful:


Comments on particle creation start at 5:26.

I won't even address the increase in the expansion rate. :-/
posted by Guy_Inamonkeysuit at 6:09 AM on May 13, 2010

Response by poster: Actually, ook, I like your answer, which popped in as I was writing my reply above. Gonna wait for a few more, but it might be yours FTW.
posted by Guy_Inamonkeysuit at 6:19 AM on May 13, 2010

Response by poster: Not a good comparison. Spiders are not social beings. If you substitute "chimpanzees" or even "dolphins" it would work better. But it still wouldn't work, because those animals haven't spent thousands of years questioning the universe in the first place and developing ever more complex and sophisticated theories and methods of probing it.

Obviously we want to understand it. That assumes that we think we can. Spiders, chimps and dolphins are arguably not even conscious as we understand consciousness (another question to ponder).
posted by Guy_Inamonkeysuit at 7:58 AM on May 13, 2010

From the linked-to Wikipedia article (emphasis mine): "Over time, the universe is expanding in space. The words 'space' and 'universe', sometimes used interchangeably, have distinct meanings in this context. Here 'space' is a mathematical concept and 'universe' refers to all the matter and energy that exist."

From that, I imagine space as being infinite and empty and the universe as being the locus of all matter - a subset of 'space' - expanding, as that matter recedes from the center of the big bang. Much like a debris cloud during the first few milliseconds after a stick of dynamite explodes in an empty room. The analogy probably fails in more ways than it satisfies, but it just gave me an (apparently) better handle on the concept. Thanks for asking the question, and to ghharr for the WP link.
posted by TruncatedTiller at 8:07 AM on May 13, 2010

From that, I imagine space as being infinite and empty and the universe as being the locus of all matter - a subset of 'space' - expanding, as that matter recedes from the center of the big bang. Much like a debris cloud during the first few milliseconds after a stick of dynamite explodes in an empty room.

From my limited layman's understanding, that's not it. There's not some infinite space that exists outside the bounds of the universe for the universe to expand into. Space, its boundaries, the spatial dimensions, these are parts of the expanding universe.

Shortly after the big bang all space and dimensions were compressed into a very small, er, volume (I'm trying not to say the word "space"). This volume is expanding. I visualize it like a growing sphere, except there's nothing outside of the sphere. Existence is only a well-defined concept inside of the sphere. There is no existence outside of the sphere because there is no "outside" outside of the sphere, not even empty space, not even nothingness.

Is the universe finite or infinite? I've an infinite universe compared to a Pac-Man screen. When you approach the edges perhaps you wrap around to the other side. That's just an analogy but it gives an idea of how the universe can simultaneously have boundaries and yet be infinite--if if is infinite.

Again apologies to any physicists out there, I understand that the universe isn't really a growing sphere or a Pac-Man level. The real concepts are impossible to visualize, though.
posted by Khalad at 8:26 AM on May 13, 2010

Response by poster: The problem with the analogy, Trunc, is that space is what is being created. At (and before) the moment of the Big Bang, there was no space. This, as I understand it, is why there is no center to the universe. It already is the center. We are, in effect, still "inside" the singularity.

I'd like to know what caused the Big Bang and what happened before that, too, but I figure that one mind-stretcher at a time is enough.

And time! What the fuck is that all about?!

posted by Guy_Inamonkeysuit at 8:31 AM on May 13, 2010

Response by poster: Whoops, Khalad beat me to it,
posted by Guy_Inamonkeysuit at 8:32 AM on May 13, 2010

I think a common problem is that when most people imagine the Big Bang, they envision a huge, empty "blackness" and suddenly a literal explosion goes off in the middle and starts expanding to fill this blackness. At least, that's how I thought about it for a long time. I imagined that the Big Bang was an explosion of all the "stuff" (matter, energy, and what-not) that we see around us and that it's moving outward into that blackness.

But that's not really how it works.

The Big Band created time and the spatial dimensions. There isn't anything outside of that "stuff". The limits of the spatial dimensions themselves are "expanding" outwards. It might help to think of them as "getting larger" instead of expanding. It's a pretty different way of looking at things, but if you really accept that the spatial dimensions themselves are part of the Big Bang, then you'll realize that asking what it's expanding "into" is a meaningless question.
posted by RobotNinja at 9:35 AM on May 13, 2010

Response by poster: Which leads us to: what was the Big Bang, and why?

You'd think I'd have more pressing things to think about. And you'd be right. But I still puzzle over this. Something set the universe in motion. And there was something to set in motion. So we have cause and effect... the first of each. We know the effect -- we're part of it. That leaves us with an unanswerable question.
posted by Guy_Inamonkeysuit at 10:29 AM on May 13, 2010

Something set the universe in motion. And there was something to set in motion. So we have cause and effect... the first of each. We know the effect -- we're part of it.

This kind of thinking has literally kept me up at night. There is absolutely no reason for anything to exist that I can even begin to comprehend. But things do exist. And that scares the crap out of me, like when I'm staring up from the bottom of an incredibly tall building and getting dizzy. So I feel your pain. I've mostly come to accept that even if we figure out why the big bang happened or if there was something before the big bang we will have at least one more question to answer.
posted by Green With You at 11:04 AM on May 13, 2010

Response by poster: It doesn't scare me -- it fascinates me. Here we are, part of an immense (and generally beautiful) system far too immense and complex for us to understand. WTF? I'd be happy just to be asking the right questions; I don't expect any good answers.

But it would be nice to know, is all I'm saying.
posted by Guy_Inamonkeysuit at 12:40 PM on May 13, 2010

I read somewhere that the universe behaves as an expanding four-dimensional sphere (with time being the fourth dimension?). In a 3D sphere, the surface is a 2D entity, and like Khalad and floam said above, if you keep going in the same direction you end up at the starting point; with the universe being an expanding 4D sphere, its surface would be a 3D entity (the universe as we perceive it), with everything moving ever farther apart like two ink points in an inflating balloon. Space itself is created during this expansion.

I have no idea if this is any way a valid analogy, not even mathematically, as I can't grasp the concept of four dimensions. So take all of this with a grain of salt of astronomical proportions.
posted by Bangaioh at 2:28 PM on May 13, 2010

Also, since we are limited by the speed of light, we can only see stuff that's a certain distance away. There could be a Norse God charging at us on the Flying Spaghetti Monster, we just can't see it yet.

Yes and no. The universe is 13.7 billion years old so you would think that we can't see anything further away than 13.7 billion light-years but in fact the edge of the observable universe is 46.5 billion light-years due to the expansion.
posted by Rhomboid at 5:40 PM on May 13, 2010

« Older Host-to-host megatransfer   |   Recommendation for movers from Philly to NYC Newer »
This thread is closed to new comments.