## Bosons and Fermions

Elementary particles such as electrons, quarks, neutrinos, protons and neutrons are fermions. Photons4 are examples of bosons. Elementary particles have an intrinsic spin or turning motion, which must be a multiple of 1/2 due to quantum mechanics. Bosons are particles with integer spin such as 0, 1, 2, and so on. Fermions are particles with half-integer spin such as 1/2, 3/2, 5/2, and so on. A particle with spin 0 does not spin at all. Since electrons, quarks, neutrinos, protons and neutrons have spin 1/2, they are fermions. A bound state8 consisting of two fermions is a boson because the spins of the two fermions add or subtract to give an integer spin. For example, a bound state of two quarks has spin 1 if the two quarks spin in the same direction. If they spin in opposite directions, the spins subtract and the bound state has spin 0. In either case, a boson is obtained. In general, a bound state of an even number of fermions is always a boson. For example, since the helium-4 nucleus consists of four fermions -- two protons and two neutrons, it is a boson. In general, a bound state of an odd number of fermions is always a fermion. For example, since the helium-3 nucleus consists of three fermions -- two protons and one neutron, it is a fermion. A bound state of any number of bosons is always a boson because you can never add or subtract integers to obtain a half-integer.

The information in this webpage is obtained from The Bible According to Einstein.