I find this site about "Big Bang", but some of them are difficult for me to read.
The Big Bang is talking about the begining of the universe. The scientists believe that the universe has expanded from a very hot and dense initial condition in around 13.3~13.9 billion years ago. And it has been expanding to now and become very big. So it means the distance of everything are getting farther and farther, it also means the distance fo everything used to be very close. In the universe, there is a thig called "Dark energy", it can make the expending of the universe faster.
1.Estimated distribution of dark matter and dark energy in the universe.
74% of the universe are dark energy
