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Quark
The smallest known building block of matter.
ParticleMicro-World
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Three quarks bound into one of nature's most stable forms.
Picture this
If a proton were the size of a basketball, the atom it lives inside would be wider than a small city.
A proton is a tiny ball of three quarks — two up and one down — held together by a roaring sea of gluons. Stack enough of them together with neutrons and electrons and you build every element from hydrogen to uranium. Protons appear so stable that we have never measured one decay.
Glossary
Did you know?
A free proton has never been observed to decay. The current lower limit on its half-life is more than 10³⁴ years — many trillion times the age of the universe.
Last updated 2026-05-17
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Scale
Three quarks bound into one of nature's most stable forms.
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