• Every minute, countless muons rain down from space, passing through everything-including us-before penetrating deep below the Earth’s surface. • The discovery of these particles, created when cosmic rays hit our planet’s atmosphere, was one of the biggest surprises in the history of particle physics. • In the mid-1930s, two sets of physicists independently found evidence of muons in tracks left behind by cosmic rays. • At the time, only a handful of particles-such as electrons, protons and photons-were known. • The muon, a heavier and shorter-lived cousin of the electron, was an unexpected new member of the subatomic family. • Upon first hearing evidence that muons might exist, the physicist and Nobel laureate Isidor Isaac Rabi famously quipped, “Who ordered that?” “This was an era where physicists thought they had the parts needed to explain what the world was made of,” says David Kaiser, a physicist and historian of science at the Massachusetts Institute of Technology.
Article Summaries:
- Muons, subatomic particles discovered in the mid‑1930s when cosmic rays struck Earth’s atmosphere, surprised physicists by adding a new, heavier cousin of the electron to the known particle roster. Their discovery prompted the realization that the universe contained many unknown particles, ultimately leading to the formulation of the Standard Model, which still underpins modern particle physics. Although the model explains most subatomic behavior, it leaves gaps such as dark matter and matter‑antimatter asymmetry. Beyond theory, muons’ deep‑penetration ability has spurred practical uses-from muography revealing hidden chambers in the Great Pyramid to applications in volcanology, material science, and medical imaging.
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