What evidence is there to prove the theory of Big Bang

Please cite your sources. I want to know more.

Thanks!

Joel is partly right, but has confused local galaxies with further ones. Let's put that right first. Our galaxy, the Milky Way, is gravitationally bound with about 35 others in what we call the Local Group. Further galaxy groups are certainly moving away, or more accurately, the space between them is expanding. We can measure that expansion pretty accurately, and if you think of it as a movie, and run it backwards, at a point in the past, everything in the Universe is in the same infinitesimally small spot. In fact, that spot IS the Universe. The temperature of the background radiation is also precisely what we would expect from all the other observations, and they point to a time of creation of 13.7 billion years ago. We also know that in the very early Universe, the expansion was much faster than the speed of light, and this has resulted in the Universe being in a sense two universes, the part we can see, which we call the Observable Universe and the part we can't see because it's light has not had time to reach us. Our measurement of this also agrees with the evidence sited above. Every observation we can make agrees with that 13.7 billion years being the age of the Universe. However, theories, by definition, are never proven, merely refined to a point where we can be pretty certain they are as accurate as we can make them. My sources are actually myself as a teacher of astronomy to grad students, but I'm sure your local library will have a number of books on the subject, and I can recommend authors such as Brian Greene and Steven Weinberg as being comprehensible to non-specialists.

The universe is expanding, this is observable and has been proven by astronomers who have recorded the positions of the stars. It stands to reason that this means that they were once closer together. Also energy dissapates. This is why heat rises, heat is energy. Anyone who has paid attention in their science classes is capable of a rudimentary understanding of the big bang theory. This is why it is a popular theory. It's pretty easy to understand if you have gotten at least a B in basic science classes. If not you should pay more attention in school.