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Particles in the universe come in two types, named bosons and fermions, after Satyendra Nath Bose and Enrico Fermi (“boson” is pronounced with a long ‘o’ and a hard ‘z’, to rhyme with “goes on”). Bosons include things like photons (particles of light), which can be absorbed or emitted in large quantities. Fermions include things like electrons and protons which form the building-blocks of matter. The chief distinguishing characteristic of these different types of particle is that bosons can congregate together in the same region of space and state of motion, all moving along together. Fermions, by contrast, only ever exist one at a time in any given place and state of motion. Photons in a laser beam are an example of bosons gathered together in the same motion. Electrons in different orbitals in atoms are an example of fermions avoiding one another. This leads to the fact that atoms with different numbers of electrons behave differently, which is the basis of chemistry.