What is antimatter?

Matter particles constitute almost everything we see in the universe. The atoms are formed by protons, electrons, neutrons, and more particles of smaller size. Even if it may seem like a thing that comes from science fiction, antimatter is real, and, in fact, it is produced every day on Earth.

What is antimatter?

Almost every particle in the universe has its own particle of antimatter, or antiparticle. These are particles that are identical in all aspects, but they have a contrary electric charge. For example, an electron has a mass of 9.1*10-31 kg, and a charge of -1. On the other side, its antiparticle, called positron, has the same mass but a charge of +1.

However, some particles don’t have an equivalent in antimatter. For example, force-transmitting particles, such as the photon, the Higgs boson, etc., are generally their own antiparticles.

When a particle and its antiparticle come into contact they annihilate each other, disappearing in a burst of light. In fact, antimatter is the most efficient fuel that exists, as it transforms all matter into energy, and, according to the famous equation of Einstein E=mc2, a small quantity of matter contains an enormous quantity of energy.

Discovery and production of antimatter

The British physicist Paul Dirac predicted antimatter in 1928, while he was trying to combine quantum mechanics with Einstein’s theory of relativity. Dirac searched for solutions to an equation that described an electron travelling at almost the speed of light. “Just as the equation x2=4 can have two possible solutions (x=2 or x=-2), Dirac’s equations could also have two solutions, one for an electron with positive energy, and another for an electron with negative energy”, according to the CERN (European Organization for Nuclear Research).

Even if at first Dirac hesitated to share his results, he finally decided to publish them, affirming that each particle in the universe has an equivalent particle that behaves identically, but that has an opposed charge.

Positrons were discovered a few years later by the physicist Carl Anderson, while he was studying cosmic rays that hit the Earth’s atmosphere, producing a cascade of other particles. In the detectors, Anderson observed a particle with the same mass as the electron, but with a positive charge: the positron.

Nowadays antimatter is regularly produced in the LHC (the biggest particle collider in the world). The collisions of the particles, that travel at near-light speeds, generate small quantities of antimatter, which has to be conserved in empty spaces to prevent it from annihilating with normal matter.

Antimatter particles are also produced through natural processes. For example, the energy of thunderstorms creates positrons, just as when cosmic rays hit the Earth’s atmosphere. The radioactive decay of some atoms can also be a source of positrons.

The mystery of antimatter

Physics predicts that in the Big Bang, matter and antimatter should have been created in equal quantities. As matter and antimatter behave identically, they should have annihilated each other at the beginning of the universe, leaving nothing behind.

The reason why matter came to dominate over antimatter is a problem still to solve, even if it is theorised that the key could reside in neutrinos.

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