The Casimir Effect and the Vacuum Energy: Duality

Abstract The Casimir effect is usually interpreted as arising from the modification of the zero point energy of QED when two perfectly conducting plates are put very close to each other, and as a proof of the “reality ” of this zero point energy. The Dark Energy, necessary to explain the acceleration of the expansion of the Universe is sometimes viewed as another proof of the same reality. Recently, several physicists have challenged the usual interpretation, arguing that the Casimir effect should rather be considered as a “giant ” van der Waals effect. All these aspects are shortly reviewed.