Visual Timeline of the Universe

The Big Bang occurred an estimated 15 billion years ago. The universe began with a cataclysm that created space and time, as well as all the matter and energy the universe will ever hold. All the space, time, energy, and matter that constitute today's universe originated in the Big Bang. The early universe was extremely small, dense, and hot. For the first fraction of a second, only energy existed.

As the universe expanded and cooled, the four fundamental forces (gravity, electromagnetism, and the strong and weak nuclear forces) became distinct. Quarks, then atomic particles and their antimatter partners, appeared. As matter and antimatter met, they annihilated each other, leaving behind energy and a slight excess of ordinary matter - almost exclusively the lightest elements, hydrogen and helium. The faint residual heat from the Big Bang can be observed coming from everywhere in the sky.