Virtual particles are a concept within quantum field theory that describes fluctuations in quantum fields. These fluctuations can be visualized as the temporary creation and annihilation of particle-antiparticle pairs.
The underlying cause of virtual particles is the inherent uncertainty and dynamics of quantum fields. According to quantum field theory, all particles are manifestations of underlying fields that permeate space. These fields can fluctuate, even in the absence of external influences.
These fluctuations give rise to the creation and annihilation of virtual particle-antiparticle pairs. These pairs are referred to as virtual because they are not directly detectable or observable as individual particles. They exist for very brief periods of time, constrained by the principles of the uncertainty principle.
Virtual particles are not directly dictated by the presence of classical particles. Rather, they arise from the inherent properties and dynamics of the quantum fields themselves. The quantum fields can fluctuate, and these fluctuations can manifest as virtual particles.
It is important to note that virtual particles are primarily a mathematical concept used in the framework of quantum field theory to describe and calculate the behavior of particles and interactions. They are not directly observable or measurable in the same way as real, on-shell particles. However, their effects can be indirectly observed through various phenomena, such as the Lamb shift or the Casimir effect, which arise from the influence of virtual particles on physical systems.