At the high temperatures achieved in the very young Universe, not only can particles and photons be spontaneously created, given enough energy, but also antiparticles and unstable particles as well, resulting in a primordial particle-and-antiparticle soup. (BROOKHAVEN NATIONAL LABORATORY)

What Was It Like When The Universe First Created More Matter Than Antimatter?

The Universe was born with equal amounts of matter and antimatter. How did matter win?

13.8 billion years ago, at the moment of the Big Bang, the Universe was the hottest it’s ever been in history. Every single known particle exists in great abundance, along with equal amounts of their antiparticle counterparts, all smashing rapidly and repeatedly into everything around them. The spontaneously create themselves from pure energy, and annihilate away into pure energy whenever particle-antiparticle pairs meet up.

Additionally, anything else that can exist at these energies — new fields, new particles, or even dark matter — will spontaneously create itself under these conditions, too. But the Universe cannot sustain these hot, symmetric conditions. Immediately, it not only expands, but cools. In a fraction of a second, these unstable particles and antiparticles vanish, leaving a Universe favoring matter over antimatter. Here’s how it happens.

The early Universe was full of matter and radiation, and was so hot and dense that it prevented all composite particles, like protons and neutrons from stably forming for the first fraction-of-a-second. Once they do, however, and the antimatter annihilates away, we wind up with a sea of matter and radiation particles, zipping around close to the speed of light. (RHIC COLLABORATION, BROOKHAVEN)

At the moment of the Big Bang, the Universe is filled with everything that can be created up to its…