What is at the edge of the Universe ?

That's an interesting question. The short answer is that there isn't any "edge" to the Universe, as in the edge of your school grounds where there is more property beyond. Science fiction and other dimensions aside, the best way of looking at the Universe is to think of the surface of a balloon. Right now the "balloon" is expanding (being blown up) so the distance between any two points on the balloon is increasing. However, there is no edge to the surface of the balloon. This is where cosmologists (people who study the physical nature and evolution of the Universe) and relativists (people who study Einstein's general theory of relativity) talk about a curved space-time continuum.

One observable effect of this geometry for the Universe is if we look far enough in any direction, we see the same thing. Because light does not travel infinitely fast, the farther into the distance that we look, the farther back into time that we look. In astronomy there is something called the cosmic microwave background. This radiation is left over from the "big bang", the event at the start (in time) of our Universe.

Check out your library and its reference section for books on astronomy for more information.

This question is from Steve Snowden at the Imagine the Universe website which can be found at: http://imagine.gsfc.nasa.gov/