The Fermions and Bosons are two Class of particles in the Standard Model of particle physics. The particles in these groups are distinguished by their value of quantum spin. Similar to how the unit of mass is kg and the unit of length is meters, the unit for the spin of quantum particles is the Reduced Planck Constant denoted by H-bar (ℏ). ℏ is equal to h/2π when represented in terms of the Planck Constant (h).
The Fermions have a spin that is a half-integer multiple of the reduced Planck constant, for example – 1/2, 3/2, 5/2 etc. Physicist have only ever observed a spin of 1/2. but, what does this 1/2 spin mean anyway? A spin of 1/2 implies that a particle has to rotate twice or by 720 degrees in order to regain its initial state or configuration. Particles that fall under the Fermions category are the Electrons, muons, tau, neutrinos and the Quarks. All these particles have a spin of 1/2.
The Fermions make up all the matter in the universe and are therefore called matter particles. The quarks make up protons (2 up, 1 down) and neutrons (2 down, 1 up), which then form a nucleus which is surrounded by a cloud of electrons.
The Bosons have a spin that is an integer multiple of the reduced Planck Constant like- 1,2,3 etc. All Bosonic particles are the exchange particles or the force carrying particles. Particles with many different integer spins have been discovered. For example, the Higgs Boson and the Z Boson have a spin of 0, the Photon, the W Boson and the Gluon have a spin of 1. The Graviton, which is a hypothesized force carrying particle of gravity has an expected spin of 2.
Other facts about the Fermions and Bosons
There can exist numerous bosons of the same kind and quantum state in one place at the same time, But, not 2 or more similar Fermions can exist in the same quantum state at the same place at the same time. This is known as the Pauli Exclusion Principle. The principle was devised by Wolfgang Pauli in 1926 and was initially applicable to only electrons. the principle stated that no two electrons in an an atom can have the same set of quantum numbers Later on, in 1940, this rule was extended to all half-integer spin particles, the Fermions. The Bosons don’t follow this principle. instead, they follow the Bose-Einstein Statistics.
The Boson was named after an Indian Physicist, Satyendra Nath Bose for his contributions to the field of Quantum physics.