Bosons and fermions are two fundamental classes of particles in quantum physics, and they have distinct properties and behaviors. While fermions are associated with matter particles such as electrons, protons, and neutrons, bosons are responsible for carrying forces between particles. Here's why bosons are typically the carriers of forces:
Quantum Field Theory: The framework used to describe particle physics is known as quantum field theory. In this theory, particles are treated as excitations of their respective quantum fields. Bosons are associated with force-carrying fields, also called gauge fields or vector fields. These fields permeate space and interact with other particles, transmitting the forces between them.
Integer Spin: Bosons have integer values of spin (angular momentum) such as 0, 1, 2, etc., in natural units, while fermions have half-integer spins like 1/2, 3/2, 5/2, and so on. This distinction is a consequence of the spin-statistics theorem, which states that particles with integer spins follow Bose-Einstein statistics, while particles with half-integer spins follow Fermi-Dirac statistics. The Bose-Einstein statistics allow bosons to occupy the same quantum state, which is crucial for the formation of force-carrying fields.
Exchange Symmetry: Another important principle in quantum mechanics is the exchange symmetry of identical particles. Fermions obey the Pauli exclusion principle, which states that no two fermions can occupy the same quantum state simultaneously. This property prevents fermions from easily clustering together and forming force-carrying fields. On the other hand, bosons do not have this restriction, and multiple bosons can occupy the same state. This property enables the formation of coherent bosonic fields, which are responsible for transmitting forces.
Mediating Particles: The bosons associated with each fundamental force are known as gauge bosons or force mediators. For example, the electromagnetic force is carried by photons (the bosons of electromagnetism), the strong force is carried by gluons, the weak force is carried by W and Z bosons, and the gravitational force is hypothesized to be carried by hypothetical particles called gravitons. These force mediators facilitate the interaction between particles, allowing forces to be transmitted.
In summary, bosons, with their integer spins and ability to occupy the same quantum state, are well-suited for carrying forces between particles. This role arises from the fundamental principles of quantum mechanics and the properties of particles in the Standard Model of particle physics.