Introduction

Abstract

This book is about (electromagnetic) dispersion forces. These forces appear between all objects in the universe. They are weak but may still be the dominating forces on the micrometer and nanometer scales. They were first discovered empirically, for atoms and molecules, by J. D. van der Waals [1] in the 1870s in his research on liquids and gases. The origin of the forces was not understood until much later. F. London [2], gave the explanation in terms of fluctuating dipoles in 1930, an explanation that prevails today. The forces were named after van der Waals. The potential varies with distance, r, as r- 6 and the attractive force as r- 7. The idea of intermolecular forces was not new and the correct distance dependence was predicted already by T. Young [3] in 1805; the correct origin of the interactions was proposed by P. N. Lebedev [4] in a speculative manner in 1894, inspired by the work by H. Hertz [5]. Generalization of these forces are acting between larger objects of mesoscopic and macroscopic size. Here, they are caused by fluctuations in the charge- and current-densities in the objects. The force depends on the shape and material of the objects. If the objects are submerged in a fluid the force can even be repulsive [6–8]. Even with vacuum in between the objects the force can in principle be repulsive for metamaterials of chiral type but the initial suggestions that the sign of the force in vacuum could be altered by metamaterials turned out to be unrealistic [9].