The concept of virtual photons and normal photons is rooted in quantum field theory, specifically in the framework of quantum electrodynamics (QED), which describes the electromagnetic interaction. While both types of photons are related to the electromagnetic force, they have distinct properties and roles.
Normal Photons: Normal photons are the fundamental particles of light and electromagnetic radiation. They are the carriers of the electromagnetic force and mediate interactions between charged particles. Normal photons are real particles that can be emitted or absorbed by charged particles during electromagnetic interactions. They have a well-defined energy, momentum, and polarization and can be detected as electromagnetic waves or particles in experiments. Normal photons obey the laws of conservation of energy and momentum.
Virtual Photons: Virtual photons, on the other hand, are not directly observable as free particles. They are internal lines in Feynman diagrams used to calculate the behavior of interacting charged particles in quantum field theory. Virtual photons are associated with the exchange of energy and momentum during the interaction process but do not correspond to actual, measurable particles in the same way as normal photons. They are a mathematical construct used to simplify calculations and describe the electromagnetic interaction within the framework of perturbation theory.
In the case of electron-electron repulsion, the exchange of virtual photons plays a crucial role. According to quantum electrodynamics, electrons repel each other due to their electric charges. This repulsion is mediated by the exchange of virtual photons between the electrons. The exchange of virtual photons effectively transfers energy and momentum between the electrons, resulting in the repulsive force.
It is important to note that virtual photons are not the same as normal photons. They do not propagate freely through space, nor do they have the same properties as real photons. Their existence is tied to the mathematical framework of quantum field theory and the perturbative calculations used to describe the behavior of interacting particles.
In summary, normal photons are the physical particles of light and electromagnetic radiation, whereas virtual photons are mathematical constructs used to describe interactions between charged particles within the framework of quantum field theory. The exchange of virtual photons is a fundamental aspect of the electromagnetic force, including the repulsion between electrons.