The Big Bang

No one truly knows how to describe the Big Bang. We can sort of imagine it as a gigantic explosion. But a typical explosion expands into space. The Big Bang, however, was an explosion of space. Space didn’t exist until the Big Bang. In fact, the Big Bang was not only the beginning of space, it was also the beginning of energy and matter.

Ever since that cataclysmic beginning, the universe has been cooling. Hotter things have more energy. And physicists know that things with very high energy can flip back and forth between existing as matter or as energy. So you can think of this timeline as describing how the universe gradually changed from being pure energy to existing as different mixes of matter and energy.

And all of it began with the Big Bang.