Every Particle Has an Antiparticle — and When They Meet, Both Are Destroyed

A Mirror of Matter

In 1928, British physicist Paul Dirac was attempting to reconcile quantum mechanics with special relativity, producing a new wave equation for the electron. When he examined the solutions of his equation, he found something unexpected: along with the electron solutions he expected, the mathematics predicted a second class of solutions describing a particle identical to the electron in mass but with the opposite electrical charge. There was no such particle known at the time.

Rather than dismissing this as a mathematical artifact, Dirac made a bold prediction: this particle must exist. In 1932, Carl Anderson discovered it experimentally in cloud chamber photographs of cosmic rays. He named it the positron — the antielectron. Dirac's prediction was confirmed, and the concept of antimatter was born. For every fundamental particle in nature, there exists a corresponding antiparticle with the same mass but opposite values for charge and certain other quantum numbers.

The Annihilation Event

When a particle meets its antiparticle, both are completely destroyed in a process called annihilation, converting their combined rest mass energy entirely into high-energy photons — gamma rays. An electron-positron pair annihilates to produce two gamma-ray photons, each carrying the electron's rest mass energy of 511 kiloelectronvolts, flying off in opposite directions to conserve momentum.

This conversion is total and instantaneous. No fragment of the original particle or antiparticle remains. All of the rest mass energy described by E=mc² is released as radiation. This is why antimatter, however small the quantity, represents an extremely powerful energy source in principle — a kilogram of antimatter annihilating with a kilogram of matter would release approximately 43 megatons of energy equivalent, more than the largest nuclear bomb ever detonated.

Producing and Storing Antimatter

Producing antimatter requires enormous energy inputs, because it must be created from pure energy in particle accelerators. CERN's antiproton decelerator facility produces antihydrogen — atoms consisting of a positron orbiting an antiproton — by bringing antiprotons and positrons together at low enough energies to allow binding. The amounts produced are minuscule: a few million atoms at a time, far too few to weigh. Storing antimatter is equally challenging: any contact with ordinary matter causes immediate annihilation, so antiparticles must be suspended in electromagnetic traps that prevent them from touching the container walls.

In medicine, antimatter is already in everyday clinical use. Positron emission tomography — PET scanning — works by injecting patients with a radiotracer that emits positrons. Those positrons quickly annihilate with nearby electrons, producing pairs of gamma rays that fly off in opposite directions and are detected simultaneously, allowing precise three-dimensional imaging of metabolic activity inside the body.

The Deepest Mystery: Why We Exist

The existence of antimatter raises the most profound question in cosmology. The Big Bang should have created equal amounts of matter and antimatter. If that had happened, all of it would have annihilated, leaving a universe of pure radiation and nothing else — no stars, no planets, no atoms, no observers. Yet here we are.

Something in the first moments of the universe produced a tiny excess of matter over antimatter — roughly one extra particle of matter for every billion particle-antiparticle pairs. After annihilation, that tiny residue of ordinary matter is what remained and what went on to form everything in the observable universe. This asymmetry, called baryogenesis, is one of the central unsolved problems of physics. Experiments at CERN are studying subtle differences in the behavior of matter and antimatter particles, searching for the physical asymmetry that explains why the universe is made of something rather than nothing.