In Feynman diagrams, virtual photons are not literal particles that are emitted and absorbed by electrons. Instead, they are mathematical representations used to describe the interaction between charged particles, such as electrons, through the electromagnetic force.
When two electrons repel each other, the interaction is mediated by the exchange of virtual photons. This exchange is described using a virtual photon line in the Feynman diagram. The virtual photon represents the exchange of energy and momentum between the electrons.
In quantum field theory, the fundamental forces are understood as interactions between particles through the exchange of gauge bosons. In the case of electromagnetic interactions, the gauge boson is the photon. However, it's important to note that the virtual photons in Feynman diagrams should not be interpreted as actual particles that exist independently in space and time. They are mathematical constructs used to calculate the probabilities of different particle interactions.
In summary, in a Feynman diagram, the virtual photon represents the exchange of energy and momentum between charged particles, but it is not a physical particle that is emitted or absorbed in the traditional sense.