matterantimatter

Antimatter refers to particles that have the same mass as their corresponding matter particles but opposite electric charge and other quantum numbers. For every particle there is an associated antiparticle, such as the positron (antiparticle of the electron) and the antiproton. When a particle and its antiparticle meet, they annihilate, converting their mass into energy, usually in the form of gamma photons and, at higher energies, other particle products.

Antiparticles can be produced in high-energy processes such as particle collisions or pair production from energetic photons. In the early universe, matter and antimatter were created in nearly equal amounts, but small asymmetries—through mechanisms collectively referred to as baryogenesis and CP violation—led to a surplus of matter that survives today.

Antimatter is rare in nature on Earth. Most antimatter is created in particle accelerators and annihilates rapidly upon contact with ordinary matter. Nevertheless, laboratories have created and even trapped neutral antihydrogen atoms, enabling tests of fundamental symmetries and properties of antimatter.

Antimatter has practical uses in science and medicine, most notably in positron emission tomography (PET) imaging, which relies on positron annihilation. It also serves as a tool for probing fundamental physics and as a staple of theoretical discussions about energy density, propulsion, and cosmology, though widespread applications remain speculative.