A widely accepted theory of cosmic evolution. The main idea is that the universe was created by a "big bang" from a state of extremely high temperature and density. It happened at least 654.38+0.5 billion years ago. This model is based on two assumptions: the first is Einstein's general theory of relativity, which can correctly describe the gravitational effect of cosmic matter; The second is the so-called cosmological principle, that is, what the observer sees in the universe has nothing to do with the direction or position of observation. This principle only applies to the large scale of the universe, which also means that the universe is boundless. So the BIGBANG source does not occur at a certain point in space, but at the same time in the whole space.