In quantum field theory, particles interact with each other through the exchange of virtual particles, which are quantized excitations of their respective fields. This interaction is mediated by fundamental forces, such as electromagnetism, the weak force, the strong force, and gravity (though a complete quantum theory of gravity is still an open problem).
Let's take the example of two electrons interacting via the electromagnetic force. In quantum electrodynamics (QED), which describes the electromagnetic interaction, electrons are represented as excitations of the electron field. The electron field permeates all of spacetime. When two electrons interact, they exchange virtual photons, which are excitations of the electromagnetic field.
The process can be understood through the following steps:
Electron Excitation: Each electron is associated with an electron field. The presence of an electron can be understood as a localized excitation or disturbance in the electron field.
Virtual Photon Exchange: The interaction between the two electrons occurs through the exchange of virtual photons. One electron emits a virtual photon, and the other absorbs it. This exchange occurs within the realm of quantum uncertainty, following the rules of quantum field theory.
Field Mediation: The virtual photon acts as a mediator between the two electrons. It carries the electromagnetic interaction, carrying energy, momentum, and electric charge.
Interaction Outcome: As a result of the exchange, the electrons experience a change in momentum and energy. This change can lead to repulsion or attraction, depending on the circumstances of the interaction.
This exchange of virtual particles is a fundamental concept in quantum field theory. It allows for the description of particle interactions and the computation of probabilities for different outcomes. The theory is successful in describing a wide range of phenomena, such as the scattering of particles, the behavior of atoms and molecules, and the properties of fundamental particles.
It's worth noting that the specific details of particle interactions vary depending on the forces involved and the particular quantum field theory describing them. Each force has its own mediator particle and associated field. For example, the electromagnetic force involves photons and the electromagnetic field, while the strong force involves gluons and the quantum chromodynamics (QCD) field. The principles of quantum field theory provide a framework for understanding these interactions within the context of quantum mechanics.