Q&A: What is the big bang theory, how did the universe come into existence?

How did it occur? Please give an answer as detailed as you want describing the Big Bang theory in an understandable way. Thank you for answering!

Question #3, written and asked on Might 19, 2009
Koen: Please really answer the question rather then telling me to go to wikipedia, your answer is useless and I don’t even recognize why you bothered answering.
Joe: It is not homework
Here’s the spelling, Georges Lemaître, is the person who proposed the Big Bang theory.