An expanding universe generally has a cosmological horizon which marks the boundary of the part of the universe that an observer can see given that photons have to travel from the object to us, before we can see them. This is also called the observable universe, which is always and forever changing due to our technological advances. The observable universe is a sphere and centers the observer, meaning that each and every one of us is in fact, the center of the observable universe. Radiation emitted by objects beyond the cosmological horizon never reaches the observer, because the space in between the observer and the object is expanding too rapidly.
The universe is said to be "everything there is" but really, who is there to say there isn't something there outside of everything? The universe is really just this evenly dense ever expanding mass of stuff that we can study and that we have learned many fascinating things about!
A lot of people say the universe is expanding, it HAS to be expanding into something, and if it's expanding into something there has to be an edge. NO NO NO.
The universe is not expanding in the way a human being with the average vocabulary would think. It's just expanding. Let me explain. The Big Bang was not an explosion in the way we think of it. There was no single point that which matter came flying out in all different directions. After the cosmological event of the Big Bang, every bit of matter was evenly spaced, and remains that way, other than that gravity makes little clumps now and then.
When it is said that the universe is expanding it is meant that the fabric of the universe is expanding. Stretching like a piece of elastic. If you were to find the point of which the Big Bang started it would be everywhere. (As I said, no single point)
Obviously we're not sure if the universe is infinite, though current data suggests that it is. SO it is quite possible that the universe is infinite, and expanding, which just confuses everyone who crosses the path of this subject.
If there is an edge, we ill never see it, and never know it. One possible explanation to this is the polyhedral theory, which I may explain at a later date.
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