Given the amount of matter left in the Universe, some of our antimatter must be missing
The qualities of particles and antiparticles are diametrically opposed, such as electric charge. The positive positron, for example, is the antiparticle of the negative electron. Every known physics process produces the same quantity of matter and antimatter.
When a particle collides with its antiparticle, it annihilates, resulting in high-energy photons. As a result, there should be no matter or antimatter in the Universe, simply a sea of photons. Instead, it contains enough matter to form two trillion galaxies and no antimatter, as far as we can tell.
The fact that the ‘afterglow’ of the Big Bang (cosmic background radiation) comprises around 10 billion photons for every particle of matter in today’s Universe provides a clue as to what happened to all the antimatter. This means that there were 10 billion and one matter particles for every 10 billion antimatter particles in the Big Bang, and 10 billion photons for every particle of matter following an orgy of annihilation.
Physicists have long sought a tiny asymmetry in the laws of physics that could explain the Big Bang’s excess of matter over antimatter. They believe they’ve discovered it in neutrinos’ behavior.
Neutrinos are ethereal subatomic particles that interact with matter only seldom. (Hold up your thumb; roughly 100 billion neutrinos per second pass through your thumbnail as a result of nuclear processes in the Sun.) Neutrinos are divided into three categories, and each one alternates between being an electron neutrino, a muon neutrino, and a tau neutrino.
Since 2016, physicists at the T2K experiment in Japan have been attempting to demonstrate that neutrinos and antineutrinos behave differently. To do so, they generate muon-neutrinos and muon-antineutrinos at a facility in Tokai and transfer them to the Super-Kamiokande detector, which is 295 kilometers down.
So far, they’ve found more electron-neutrinos and less electron-antineutrinos than expected, implying that neutrinos and antineutrinos behave differently. It’s a little effect that still has to be verified, but it could be the key to a matter-dominated Universe.
Neutrinos have insufficient mass to have made a significant impact on the Universe. However, they only spin clockwise around their direction of flight, leading physicists to speculate that neutrinos and antineutrinos in the Big Bang had super-heavy counterparts with opposing spin.
Only the high-energy circumstances of the Big Bang would have allowed these ultra-heavy particles to exist, and they would have quickly disintegrated into the particles we observe today. They could have etched their asymmetry on the cosmos in this way, producing the 10 billion and one matter particles for every 10 billion antimatter particles required to explain why we live in a Universe made entirely of matter.