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subatomic particles
The basic conception of a subject now known as
subatomic particle physics dates back to 500 BC when the Greek
philosopher Leucippus and his pupil Democritus suggested that
matter consists of small, indivisible particles, which they called
atoms. For more than 2000 years after this, the notion of atoms lay
in obscurity. For quite a long time, people believed that all
matter consisted of four elements: earth, fire, air, and water. We
now know that atoms do exist, and that some particles smaller than
atoms also exist. These subatomic particles are divided into two
main groups, the leptons and the hadrons. The best known lepton
("light" particle) is the electron. In order to account for the
emission of electrons from the nucleus, the neutrino, an
essentially massless neutral particle was postulated. The muon and
the tau, both much more massive than the electron, comprise the
rest of the lepton family. The hadrons are divided into two groups,
the mesons and the baryons. Protons and neutrons are baryons.
Mesons and baryons are made of smaller particles called quarks.
There are six different quarks: up, down, charmed, strange, top,
and bottom. While these are cool names, they convey nothing about
the distinct properties of the quark. Each quark comes in three
different colors: red blue and green. Again, the color label has
nothing to do with the quark's appearance. Baryons are composed of
three quarks, mesons are composed of a quark and an antiquark. Now
that you have probably been thoroughly confused, move on, and
hopefully that confusion will go away.
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