The Big Bang and Raisin Bread

The Big Bang was the origin of the universe, about 15 billion years ago. It explains the fact that we can see all objects receding from us, and those that are further away are receding faster. A helpful 3-D analogy is a rising loaf of raisin bread, with the raisins being the galaxies. This analogy can be misleading, however, since the real universe does not have an edge. To understand this aspect, there is a 2-D analogy to the surface of an expanding balloon.

This animation was adapted from http://map.gsfc.nasa.gov/m_uni/uni_101bbtest1.html. It shows two points after the original Big Bang - a smaller, earlier universe, and a larger, later one at which the universe has doubled in size. Really, the expansion after the initial Big Bang is smooth, not jumpy as this animation shows.

Putting the 2-D and 3-D analogies together gives a better picture than either by itself.