Part 6/9:
Virtual particles are a theoretical construct within QFT that help to explain interactions between real particles. These entities are not directly observable; they exist within the black box of quantum interactions. For example, when two electrons interact, one might imagine the exchange of virtual photons that mediate this interaction.
Feynman discovered that while considering many potential interaction scenarios might seem overwhelming, the contributions of more complex interactions diminish rapidly. Thus, calculating a few probable possibilities could yield remarkably accurate predictions about particle behavior.