The concept of virtual particles in quantum field theory is a mathematical tool used to describe interactions between particles. Virtual particles are not directly observable, and they do not have the same status as real particles. Instead, they are a way to represent the exchange of energy, momentum, and other properties during particle interactions.
In quantum field theory, the properties of virtual particles, such as spin and charge, are determined by the rules of the theory and the specific interaction under consideration. The conservation laws of quantum field theory ensure that the properties of the virtual particles involved in an interaction match the properties of the corresponding real particles.
The conservation of electric charge, for example, ensures that virtual particles involved in electromagnetic interactions carry the same charge as the corresponding real particles. Similarly, the conservation of angular momentum dictates that the spin of virtual particles matches the spin of the corresponding real particles.
The proof of this correspondence between virtual and real particles lies in the mathematical framework of quantum field theory itself. By using Feynman diagrams, which are graphical representations of particle interactions, physicists can calculate the probabilities of various particle interactions. These calculations take into account the properties of the real particles involved, and through the mathematical framework, the virtual particles emerge consistently with the corresponding properties.
It's important to note that virtual particles are a mathematical construct and should not be thought of as literal, independently existing entities. They are a useful tool for calculating and understanding particle interactions within the framework of quantum field theory.