text: The common picture of the universe as a big sphere of space with stars in is an inacurate proposal. It is simply given as a simple method to give an idea of the principles. Think of it as a dumbed down idea to allow people to start to get to grips with an idea that has much higher levels of complexity. The universe is not expanding into space... before the universe there was literally nothing (not even a void) and the universe isn't expanding into anything it is simply expanding. If you set off on a trip to the edge of the universe... even at faster than light speed you would not reach it, you would simply come back to where you began. The dimensions that we are limited to make the image of our universe relative to our movement the euivalent to that of moving over the surface of a sphere, but not through it - here no centre and no edge exists, yet expansion can still occur. \n\nThat doesn't really answer your question but hopefully clarifies some points raised in other answers