All particles that form matter around us, such as electrons, protons or neutrons, have equivalent versions of them in antimatter. The antimatter particles, or antiparticles, are almost identical to particles of matter, but with an opposed electric charge. For example, an electron has a negative charge, and a positron (the antiparticle of the electron) has the same mass, but a positive charge.
When a particle and an antiparticle come into contact, they annihilate each other, releasing a significant amount of energy. In the universe exists a symmetry between matter and antimatter, by which all processes create or destroy equal quantities of particles and antiparticles.
For this reason, it is believed that in the moment of the Big Bang, which represented the creation of the universe, the same amount of matter and antimatter were created. However, if this was the case, all particles would have annihilated each other, leaving the universe completely empty. There is still no definitive explanation to why matter ended up dominating over antimatter.
A possible explanation
For many years scientists have been searching some subtle asymmetry in the laws of physics that could explain the excess of matter over antimatter at the beginning of the universe. According to some recent studies, a possible solution is found in neutrinos.
Neutrinos are subatomic particles that rarely interact with matter. In fact, every second 100 trillion neutrinos generated by nuclear processes in the Sun go through your body.
In an experiment carried out in Japan called T2K, physicists have been trying to show for years that neutrinos behave differently than antineutrinos. So far they have detected more particles of matter than antimatter ones, suggesting that they have a different behaviour.
This is a very small effect that still has to be confirmed, but it could give us an explanation as to why the universe is dominated by matter. Moreover, it is thought that in the moment of the Big Bang supermassive versions of neutrinos and antineutrinos could have originated, which then would have decayed in the particles that we know nowadays.
In this process could have appeared an asymmetry between matter and antimatter, giving as a result a universe formed entirely by matter.