Prediction and discovery
In 1928 British physicist Paul Dirac combined special relativity and quantum mechanics in an equation for the electron and concluded there must be a particle with the electron's mass but positive charge. Four years later, Carl Anderson at Caltech spotted it in cosmic-ray photographs and named it the positron; the two shared Nobel Prizes in 1933 and 1936 respectively. The antiproton was created in an accelerator in 1955, and every fundamental particle has since been found to have an antiparticle partner.
Annihilation and uses
When a particle meets its antiparticle, both disappear and all their mass becomes energy, mostly gamma rays, according to E=mc². One gram of antimatter meeting matter would release roughly twice the energy of the Hiroshima bomb. Yet all the antimatter humans have ever made adds up to only tens of nanograms and costs vastly more energy to produce, so antimatter fuel or weapons remain science fiction. Hospital PET (positron emission tomography) scans, by contrast, are everyday antimatter technology: a tracer emits positrons that annihilate with electrons, and the resulting gamma rays reveal tumors.
Why is the universe made of matter?
Right after the Big Bang, matter and antimatter should have formed in almost equal amounts, yet today's universe is almost entirely matter. Roughly one extra matter particle survived for every billion pairs, and the rest annihilated into light. Why this imbalance arose is a major open question; Andrei Sakharov laid out the necessary conditions in 1967, but the Standard Model alone cannot account for it. CERN has created and trapped antihydrogen atoms, and in 2023 the ALPHA experiment showed for the first time that antimatter falls downward like matter. Alongside dark matter, it is one of cosmology's biggest unsolved problems.
FAQ
- Does antimatter fall up?
- No. CERN's ALPHA-g experiment confirmed in 2023 that antihydrogen falls down like ordinary matter. Its exact acceleration is still being measured.
- Where does antimatter occur naturally?
- Positrons are produced when cosmic rays hit the atmosphere, in lightning inside thunderstorms and in the decay of radioactive elements such as potassium-40. Even the potassium in a banana very occasionally emits a positron.
Sources reviewed: 2026-10-26
References
- Dirac, P. A. M. (1928). The quantum theory of the electron. Proceedings of the Royal Society A, 117(778), 610–624.
- Anderson, C. D. (1933). The positive electron. Physical Review, 43(6), 491–494.
- ALPHA Collaboration (Anderson, E. K., et al.) (2023). Observation of the effect of gravity on the motion of antimatter. Nature, 621, 716–722.