Virtual particles are mathematical entities used in quantum field theory calculations to describe the interactions between particles. They are not directly observable or detectable as actual particles in the same way as stable particles.
In quantum field theory, particles and their interactions are described in terms of fields that permeate all of spacetime. These fields can fluctuate and undergo interactions, and virtual particles are a way of representing these fluctuations and interactions mathematically.
Virtual particles are called "virtual" because they violate the energy-momentum relationship (E^2 = m^2c^4 + p^2c^2) that governs the behavior of stable particles. They can have energies and momenta that do not correspond to the usual mass-energy relation for stable particles. However, these virtual particles do play a role in the calculation of physical processes.
According to the principles of quantum mechanics, particle interactions occur through a process called particle exchange. When two particles interact, they can exchange virtual particles, which briefly appear as intermediate states in the interaction. These virtual particles are considered virtual because they are not directly observed or detected. They exist for a very short duration and their effects are manifested in the overall behavior of the particles involved in the interaction.
It's important to note that virtual particles are a mathematical tool used in calculations within the framework of quantum field theory. They do not have an independent existence outside of these calculations, and their role is to facilitate the description of particle interactions and the calculation of probabilities for different processes.