Of course, the matter and antimatter were constantly annihilating, creating high-energy radiation. So, a hundred thousandth of a second after the big bang, the universe contained protons, antiprotons, neutrons, antineutrons, electrons, and positrons. At the same time that quarks combined into protons and neutrons, antiquarks combined into antiprotons and antineutrons. When the universe was initially filled with a dense collection of elementary particles, those particles included almost identical amounts of matter and antimatter. But once we produce antimatter, it only stays around for a fraction of a second before finding its matter counterpart and annihilating. A PET scan, which stands for Positron Emission Tomography, uses antimatter to scan for activity in different regions of the brain. We produce antimatter all the time in laboratories, and even in hospitals. In the reverse process, if you concentrate high-energy radiation in a small enough region, the energy of that radiation can create a particle-antiparticle pair, such as an electron and positron or a quark and antiquark. That’s because when a particle collides with its own antiparticle, the two can annihilate and release their energy, usually in the form of electromagnetic radiation. We don’t see naturally occurring antimatter around us. Collectively, these antiparticles are called antimatter. For example, electrons have negative charge, and their antiparticles, called positrons, have positive charge. Most particles have corresponding antiparticles with the same mass but opposite charge. (Image: FlashMovie/Shutterstock) Antiparticles

Why? When a particle collides with its own antiparticle, the two can annihilate and release their energy, usually in the form of electromagnetic radiation.

However, after the formation of protons and neutrons, the next big change wasn’t about particles combining, instead particles were being destroyed. By Gary Felder, Smith College A hundred thousandth of a second after the big bang, the universe contained protons, antiprotons, neutrons, antineutrons, electrons, and positrons.

Matter antimatter