Different viewpoints of the Casimir effect

Lamoreaux replies: I will briefly address some of the points raised in the entertaining letter by Kim Milton and Iver Brevik. Unfortunately, there appears to be some misunderstanding of my intent: I am not proposing the nonexistence of photons or zero-point energy of the electromagnetic field; I am proposing that their introduction presents new problems that must be addressed completely and consistently. Their contribution to the cosmological constant remains a possibility.

Given the length constraints on a review article, it was not possible to touch on every aspect and application of the Casimir and related effects. My goal was to give my unique historical overview and then describe effects and applications most easily accessible to a wide audience. Several books in addition to Peter Milonni’s, which I referenced, describe the wide applications of Casimir or van der Waals forces and their generalizations—for example, books by Milton, ¹ by V. Adrian Parsegian, ² and by Vladimir Mostepanenko and N. N. Trunov. ³

As to the reported accuracy of various experiments, I prefer to not second-guess those authors, including myself. I have no illusions about the perfection of my own work, but I was careful and found the data internally consistent at the level of error I reported. I did find one calibration error and published an erratum. Given the attention I have paid to other corrections, the recent Drude-model finite-conductivity thermal correction appears incompatible with my experimental result.

A different analysis, done independently by me, Mostepanenko, Giuseppe Bimonte, and others, in which the metal plates are treated as a conducting waveguide, shows a relatively small correction and good agreement with my experimental result. Until the differences between the theoretical approaches are resolved, rejecting experimental results is premature.

As to the experiments that have yielded a 1% level of agreement with theory, the authors of those papers appear insistent that they have used no adjustable parameters. That work has gone largely unchallenged because the level of accuracy, at submicron plate separations, has not produced significant theoretical controversy; for example, the Drude-model thermal correction becomes very small for plate separations that are significantly below one micrometer.