Quantum fields are fundamental concepts in quantum field theory, a framework that combines quantum mechanics and special relativity. In this framework, particles are understood as excitations or disturbances in these quantum fields.
A quantum field can be thought of as a mathematical description that assigns a value to every point in spacetime. It is a field that permeates all of spacetime and describes the behavior of a particular type of particle. For example, there is an electron field, a photon field, and so on, corresponding to different types of particles.
Quantum fields are not composed of any specific substance in the way we traditionally think of matter. They are mathematical constructs used to describe the behavior and interactions of particles. In a sense, they are the underlying "fabric" of the universe.
When a quantum field is in its lowest energy state, called the vacuum state, it is in its ground state and devoid of particle excitations. However, when energy is added to the field, it can become excited, and these excitations are interpreted as particles. Particles can be created or annihilated by interactions between fields, and their behavior is governed by the laws of quantum mechanics.
Quantum fields and their excitations interact with each other through various fundamental forces, such as the electromagnetic force, the weak nuclear force, the strong nuclear force, and gravity (though the latter has not been fully incorporated into quantum field theory). These interactions are described by the mathematics of the theory, including equations like the Dirac equation, Maxwell's equations, and the equations of the other fundamental forces.
The behavior of quantum fields and their excitations is described by a set of principles and mathematical formalism known as quantum field theory. This theory has been incredibly successful in describing and predicting the behavior of elementary particles and their interactions at the microscopic scale. However, the ultimate nature of quantum fields and the reasons why they act as they do are still the subject of ongoing research and exploration in physics.