Why is a positron referred to as antimatter?

In the world of particle physics, the positron stands out as a unique yet fundamentally significant subatomic entity. It's an elementary particle that mirrors the properties of an electron but carries a positive charge. Because it has attributes diametrically opposed to those of an electron, it falls under the fascinating category of antimatter. The mass of a positron is identical to the electron, roughly 9.109 × 10−31 kg, but its charge, at +1.602 × 10−19 C, sets it apart.

The discovery of the positron in 1932 by Carl D. Anderson was a milestone that expanded our understanding of the microscopic cosmos. It validated the theoretical predictions of antimatter and intrigued scientists, who pondered its implications for the universe at large. Understanding the positron is fundamental in physics, not only because of its role in atomic and nuclear processes but also because it helps researchers gain insight into the elusive nature of antimatter, a cornerstone in the study of cosmic evolution and the composition of the universe.

Subatomic particles are the building blocks of the universe. The atomic realm is thriving with a vast array of particles, including electrons, protons, neutrons, and a host of other particles discovered through particle physics research. Each particle is distinct in its mass, charge, and role in the grand tapestry of matter.

Electrons are negatively charged and orbit the nucleus of an atom, affecting the atom's chemical properties. Protons, which reside at the atomic core alongside neutrons, have a positive charge and define the identity of an element — its atomic number. Neutrons are neutral, but their presence and number significantly influence atomic stability. Exploring subatomic particles provides profound insights into the forces that govern them—such as the strong and weak nuclear forces, electromagnetism, and gravity—and leads to breakthroughs in technology and medicine, including the development of exotic materials and cancer treatments.

Particle annihilation is a process that conveys the fleeting nature of existence on the quantum scale. It occurs when a particle meets its antiparticle counterpart — a cosmos-shattering handshake that concludes with both particles disappearing, leaving behind a burst of energy typically in the form of photons. This phenomenon reinforces a core principle in physics: the conservation of energy.

The dance of annihilation is not just theoretical. It has practical applications, such as in positron emission tomography (PET) scans, a medical imaging technique that exploits the annihilation of positrons to detect metabolic processes and diagnose conditions like cancer. The process also hints at profound questions regarding the creation and possible asymmetry of the universe, since an abundance of matter exists over antimatter. Understanding annihilation thus enables scientists to peek into the fundamental laws of nature, helping decipher the narrative of the cosmos from its earliest moments to its eventual destiny.