In quantum mechanics, virtual particles are entities that are used to describe certain interactions and processes. They are not directly observable or detectable like particles in the traditional sense, such as electrons or photons. Instead, virtual particles are considered as temporary fluctuations or disturbances in the underlying quantum fields that permeate all of space.
According to quantum field theory, the fundamental particles and their interactions are described in terms of quantum fields. These fields are mathematical constructs that assign a value to each point in space and time. The particles that we observe in experiments are considered as excitations or quanta of these fields.
Virtual particles arise as a consequence of the Heisenberg uncertainty principle, which states that there is a fundamental limit to the precision with which certain pairs of physical quantities, such as position and momentum, can be known simultaneously. This uncertainty allows for the temporary creation and annihilation of particle-antiparticle pairs in quantum fields.
Virtual particles can be thought of as "borrowed" energy that is briefly taken from the vacuum (the lowest energy state of a field) to facilitate interactions between other particles. They are responsible for mediating the fundamental forces of nature, such as the electromagnetic force, the weak nuclear force, and the strong nuclear force. For example, in the case of electromagnetic interactions, photons are the virtual particles that mediate the electromagnetic force between charged particles.
It's important to note that virtual particles do not obey the usual energy-momentum relation, as they are not subject to the same constraints as observable particles. They can have energies and momenta that violate the usual mass-energy equivalence relation (E=mc²) and can even have imaginary masses. However, these virtual particles play a crucial role in the mathematical framework of quantum field theory, allowing for a consistent description of particle interactions at the microscopic level.