----------------------------------------------------------------- Does the Casimir effect prove the existence of virtual particles? ----------------------------------------------------------------- The Casimir effect is the experimentally confirmed existence of a force (the Casimir force) between uncharged metallic plates in vacuum. See http://en.wikipedia.org/wiki/Casimir_effect . But don't trust the subsequent esoteric explanation given there! Indeed, since one of the derivations of the Casimir effect uses virtual particles for its derivation, some people consider the existence of this effect as evidence for the existence of virtual particles. But: 1. This is only evidence that the contribution of virtual particles cannot be neglected in certain calculational schemes based on virtual particles. 2. The effect from the virtual particles is infinite and hence physically meaningless. Only through renormalization (which destroys the naive interpration of virtual particles) can the finite, measurable effect be obtained. 3. Well-understood phenomena such as the Coulomb interaction would, by the same argument, olso have to be viewed as evidence for virtual particles since, in some calculational schemes, they arise by summing certain of the latter. But nobody seriously interprets the Coulomb force as proof of virtual particles. 4. Most important: The Casimir effect can be understood and calculated without the use of computational schemes employing virtual particles. See: R. L. Jaffe The Casimir Effect and the Quantum Vacuum http://lanl.arxiv.org/abs/hep-th/0503158 To conclude, the Casimir effect cannot be viewed as evidence for the existence of virtual particles. As their name says, and as explained in more detail elsewhere in this FAQ, virtual particles do not exist (like real particles to whioch they are contrasted in naming), in any meaningful sense of physical existence.