In quantum field theory, particles are understood as excitations or quanta of underlying quantum fields. Quantum fields are mathematical constructs that pervade all of spacetime and describe the fundamental interactions and particles in the universe.
According to quantum field theory, each type of elementary particle (such as electrons, photons, quarks, etc.) is associated with a corresponding quantum field. These fields are not fixed entities but are dynamic and fluctuate, creating and annihilating particles as interactions occur.
The behavior of particles and their interactions are described by the quantum field equations, which specify how the fields evolve in time and space. The quantum fields are operators that act on a quantum state, and their excitations correspond to particles.
Particles are observed and measured as localized entities with specific properties such as mass, charge, spin, and momentum. These properties arise from the interactions and symmetries of the underlying quantum fields. The excitations of the fields manifest as particles with specific quantum numbers and characteristics.
Quantum field theory provides a framework that combines quantum mechanics and special relativity, allowing for the description of particle interactions and the creation and annihilation of particles. It is a powerful theory that has been successful in explaining a wide range of phenomena in particle physics, including the behavior of elementary particles, the fundamental forces, and the creation and annihilation processes observed in high-energy experiments.