Scientific American: Misconceptions about the Big Bang: Overview/Cosmic Confusion

The expansion of the universe is one of the most fundamental concepts of modern science yet one of the most widely misunderstood.
The key to avoiding the misunderstandings is not to take the term "big bang" too literally. The big bang was not a bomb that went off in the center of the universe and hurled matter outward into a preexisting void. Rather it was an explosion of space itself that happened everywhere, similar to the way the expansion of the surface of a balloon happens everywhere on the surface.
This difference between the expansion of space and the expansion in space may seem subtle but has important consequences for the size of the universe, the rate at which galaxies move apart, the type of observations astronomers can make, and the nature of the accelerating expansion that the universe now seems to be undergoing.
Strictly speaking, the big bang model has very little to say about the big bang itself. It describes what happened afterward.