Unanswered Questions

Beyond the Proton, Neutron, and Electron

Why do physicists believe that there are particles inside protons and neutrons?

Ernest Rutherford (1871-1937) scattered alpha particles off gold atoms and discovered that the atom was not filled with a uniform positive material. In the same way, scattering of protons at high energies off hydrogen nuclei showed that the proton is not composed of uniform positive material. Rather, it is composed of three much smaller charged particles called quarks. The neutron is also composed of three quarks.


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