The Casimir effect is a phenomenon in quantum field theory that arises due to the influence of quantum fluctuations on the electromagnetic field. It was first predicted and named after the Dutch physicist Hendrik Casimir in 1948.
The Casimir effect occurs between two uncharged conductive plates placed in a vacuum. According to quantum field theory, the vacuum is not empty but filled with virtual particles constantly popping in and out of existence. These virtual particles are temporary fluctuations of energy and are subject to the Heisenberg uncertainty principle.
When the conductive plates are brought close together, the presence of the plates restricts the types of virtual particles that can exist between them. Specifically, virtual particles with wavelengths longer than the distance between the plates are suppressed. This leads to a decrease in the energy density of the vacuum between the plates compared to the energy density outside the plates.
As a result, there is a net imbalance of energy, and the plates experience a force pushing them together. This force is known as the Casimir force and is attractive in nature. The Casimir effect has been experimentally observed and verified, providing evidence for the existence of these vacuum fluctuations.
Regarding the question of whether virtual particles are real, it's important to understand that virtual particles are mathematical constructs used in quantum field theory to describe certain interactions. They are not directly observable or detectable as individual particles. However, their effects can be observed indirectly through measurable phenomena like the Casimir effect.
Virtual particles are considered "virtual" because they violate the energy-momentum relationship of real particles. They do not persist as stable, independent entities but exist as temporary fluctuations in the quantum fields. They play a role in various quantum phenomena and calculations within the framework of quantum field theory.
In summary, while virtual particles are not directly observable, the Casimir effect provides experimental evidence for the existence of vacuum fluctuations and the influence they have on physical systems. The Casimir effect does not imply that virtual particles become real in the sense of becoming long-lived or observable particles in isolation.