In a world where Einstein’s relativity is true, space has three
dimensions, and there is quantum mechanics, all particles must
be either fermions (named after Italian physicist Enrico Fermi)
or bosons (named after Indian physicist Satyendra Nath Bose).
This statement is a mathematical theorem, not an observation
from data. But data over the past 100 years seems to bear it
out; every known particle in the Standard Model is either a
fermion or a boson. An example of a boson is a photon. Two or
more bosons (if they are of the same particle type) are allowed
to do the same exact thing. For example, a laser is a machine
for making large numbers of photons do exactly the same thing,
giving a very bright light with a very precise color heading in
a very definite direction. All the photons in that beam are in
lockstep. You can’t make a laser out of fermions. An example of
a fermion is an electron. Two fermions (of the same particle
type) are forbidden from doing the same exact thing. Because an
electron is a fermion,