What is the raisin bread theory?

The raisin bread theory is a model of the expanding universe. The idea is that the universe is like a raisin bread. At first, before the dough rises, the raisins are distributed fairly regularly throughout the dough. As the dough rises, the raisins toward the outside rise and move away from the raisins in the center of the loaf. If our galaxy is represented by a raisin near the center of the loaf, the other galaxies move away from us - the outside of the loaf moves away at the fastest rate. The entire loaf expands in size, which means that the entire universe expands.