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If the universe keeps expanding, is it possible to travel to the edge of the universe?

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    $\begingroup$ Short answer: no, quite the opposite. The universe is infinite as far as we know it; but distances between its largest structures (superclusters of galaxies) grows. That means there are objects we will never reach, or even see as they move away, together with space surrounding them, faster than light, relative to us - so even light shining towards us moves away from us instead of getting closer. And even with us traveling at speed of light towards them, they will keep growing more distant. $\endgroup$ – SF. Jun 4 '16 at 12:54
  • $\begingroup$ No, it's expanding faster than it's possible to actually travel. Perhaps there is some way to travel from one point to another in spacetime and circumvent relativity through some loophole, but such a loophole is little more than the dreams of some theoretical physicists right now. More to the point however; the universe may not actually have an 'edge'. We know of no real bounds to the universe aside from what we can/can't see, and the boundaries of the 'observable' universe only exist because the light at that boundary can no longer get here because of my opening comment. $\endgroup$ – Logan Jun 6 '16 at 10:21
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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 this is what you are referring to, then your answer is here.

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.

The Universe is thought to be infinitely large, so it can't have a center. The center of something is the point equidistance from the edges, but if something spans infinitely long, it would just keep going. It wouldn't have an edge, and thus it wouldn't have a center. You couldn't find the point equidistant from the edges if it just spans infinitely.

The Universe is not like a ball. Rather, you can think of it like a flat grid, and its "expansion" just means that the distances between objects on the grid are getting larger. In essence, more space is being created between the objects. That's what we mean by expansion — that objects are moving away from each other, since more space is being created between them.

Here's an easy analogy: imagine you are walking your dog. Suddenly, the ground begins expanding between you. You and your dog will separated and continue receding away from each other.

That's essentially happening everywhere: space is expanding between everything, so we are drifting away from other galaxies. The Universe is infinite, and we can constantly drift apart from other objects because space is being created in between us. Here's a GIF I made that might help you get it:

enter image description here

You can see how the galaxies drift apart as the space between them increases. And this happens everywhere in the Universe. The Universe is infinite, but more and more space is being created between matter.

Fun fact: These objects can actually drift away from each other faster than the speed of light. That is, light from them eventually won't make it to us, since they'll be drifting away too quickly.

Now, this doesn't actually go against Einstein's theory that the speed of light is the fastest thing in the Universe. Einstein said that nothing can travel through space faster than light — but here, space itself is actually being created between the objects. Distances are increasing because space itself is dilating, and thus we can drift apart from other objects faster than light.

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