# Is the universe moving through infinite space time as it expands?

What I mean by this, is imagine a person blowing up a balloon. As the balloon expands, the person blowing it up is also walking. At a much grander scale, apply this concept to the universe. As the universe expands, is it also moving like the balloon through infinite space time?

I think what you're asking is a very fundamental question that doesn't really have a definitive answer. I interpreted your question slightly differently that Sir Cumference, so I'll answer it differently.

For people just learning about the expansion of the Universe, they are often taught about the analogy of the expanding balloon. The concept here is that you have a deflated balloon that you draw two dots on. These dots may represent two galaxies in the Universe defined by the surface of the balloon. The important concept here is that the surface of the balloon represents the entire universe in this scenario. The balloon is then blown up, and you notice that because of the "expansion" of the universe, the dots (i.e., galaxies) are moving farther apart. This is shown in the diagram below.

This concept is usually used to teach an important fact about our universe, namely that there is no center. At no point on the balloon can you saw that you are the center of the expansion because the expansion is happening everywhere in equal magnitude.

What you seem to be doing though, is trying to take this analogy one step further. Even though the balloon universe (ballooniverse?) is defined on the surface of the balloon and is thus two dimensional, there still exists a three dimensional space that the 2D ballooniverse is expanding into. So you question, what does that say about our 3D universe? Are we expanding into some 4D space?

That, in my opinion, is a distillation of the fundamental concepts behind your question. Assuming I'm interpreting your question correctly, then I would have to say the answer is I don't know.

There is a somewhat (unsatisfying) tautological answer in that the Universe is, by definition, everything that exists. Therefore, there can't be a 3D Universe and also a 4D space into which our 3D Universe is expanding into, because that 4D space would necessarily be a part of our Universe, by definition.

A more reasoned approach to this answer is to look at it from a mathematical perspective. If you begin to learn higher math (and by higher I mean upper undergraduate/graduate level math) you'll learn about manifolds. Manifolds are basically mathematical objects that can define things like the surface of a balloon. What you'll find is that the definition for the surface of a balloon, using the concept of manifolds, does not require that the surface exist in 3D space, even if that manifold is expanding. It is perfectly possible to define a 2D manifold that has the same topology (fancy word for structure) as an expanding balloon, without "embedding" it in 3D space. This concept makes your question kind of moot. It allows for an expanding 3D universe, without requiring the existence of some 4D space to expand into. So ultimately, I'm claiming that it is possible for a 3D Universe to exist which both has no center and is expanding, just not into a 4th dimension.

• Good explanation. Aug 17 '16 at 20:12
• I like this answer as well. Really the big reason I asked, is because I remember seeing a special on M-theory. In it, I remember a part where they talked about gravity. Basically, the force of gravity is thought to be caused by some "thing" that moves through our concept of 3 dimensional space /Universe. But that "thing" can then escape from our Universe into some other universe, void, parallel dimension, HFIL, etc. If so, has math/science shown that our Universe, even being possibly infinite in nature, moving in relation to some other planar dimension that also may be infinite. Aug 17 '16 at 20:57
• @ElBromista M-theory is mostly hypothetical and largely unfalsifiable. That said, you seem to be referring to gravitons, a hypothetical particle that carries the gravitational force. Aug 17 '16 at 21:03
• @SirCumference I upvoted your comment, but I think it should be noted that it is probably better to view "M-theory" as a framework which is a work in progress rather than an unfalsifiable theory. Aug 17 '16 at 21:12

When we talk about the universe, we are really talking about one of two things:

• The observable universe, which is everything we can possibly see.
• The Universe, which is everything that has ever existed, currently exists, and will exist.

The observable universe has its own center, usually the Earth. It is a spherical region of everything that we can see, essentially anything whose light has reached us. We usually refer to this when we say things like "there are $10^{86}$ atoms in the universe."

In reality, everyone has their own observable universe, and it can change depending on where you are. An exoplanet far away has its own observable universe, and can receive light from different places. Essentially, you are the center of your own observable universe. As more light reaches us, our observable universe will grow (or expand, if you will).

If you are referring to the latter, then there is a totally different answer and "expansion" refers to something completely different. The Universe (notice the capital "U") is all of space and time and its contents. Anything that has existed, will exist, and currently exists is part of it.

When we say the Universe is expanding, we don't mean it's like a ball that is constantly growing in size. We simply mean that the space between objects is increasing. The Universe can be infinite in size, but more and more space is being created between matter.

Another way of thinking about this is saying that space is dilating. Imagine that everything in space is on a coordinate system. The coordinate system itself is actually dilating, and thus the objects on it are drifting apart. Here's a GIF I made to help you understand it:

You can see how objects are drifting apart from each other, due to the expansion of space. Thus, your question doesn't make much sense; the Universe is all of space and it's contents, so how could it move through more space?

• Well, you give a good explanation of how the Universe is expanding, the concept of an observable universe, and the concept of time dilation. I'm not sure how to answer your question though. Would it make sense to ask, can an infinite coordinate plane we call the Universe move in relation to another infinite coordinate plane? Aug 17 '16 at 20:05
• @ElBromista Yes, that broaches on the topic of large extra dimensions and brane cosmology, but there is currently no evidence of these. Aug 17 '16 at 20:10
• @ElBromista My question was rhetorical, don't worry. But the Universe is everything, including space. It extends infinitely. Thus, your question is essentially asking "Can all of space and time and its contents move through space in relation to another 'all of space'"? Doesn't make much sense, does it? Aug 17 '16 at 20:11
• @ElBromista Also, my answer didn't touch upon time dilation. It just went over the dilation of space. Time dilation is something different. Aug 17 '16 at 20:12
• @SirCumference I'm not sure one can really make the claim that the Universe "extends infinitely". As observers all we can talk about is the Observable Universe. Anything outside this, by definition, is not observable and thus we can make no claims about it, including its very existence. It seems unlikely, but the Universe may just stop right at the edge of what we can observe. Aug 17 '16 at 20:13