Comment on “ No quantum friction between uniformly moving plates ”

All bodies are surrounded by a fluctuating electromagnetic field due to thermal and quantum fluctuations of the current density inside the bodies. This fluctuating field is responsible for many important phenomena such as the radiative heat transfer, the van der Waals interaction and the van der Waals friction between bodies. In contrast to the van der Waals interaction, for which theory is well established, the field of van der Waals friction is still controversial. As an example, different authors have studied the van der Waals friction between two flat surfaces in parallel relative motion using different methods, and obtained results which are in sharp contradiction to (for recent review of the theory of van der Waals friction see [10]). There are two approaches to the theories of the van der Waals interaction and the van der Waals friction. In the first approach which is due to Rytov [12, 13, 14] the fluctuating electromagnetic field is considered as a classical field which can be calculated from Maxwell's equation with the fluctuating current density as the source of the field, and with appropriate boundary conditions. This approach was used by Lifshitz in the theory of the van der Waals interaction [15] and by Volokitin and Persson for the van der Waals friction [8, 10]. In the second approach the electromagnetic field is treated in the frame of the quantum field theory. This approach was used in Ref.[16] to obtain the van der Waals interaction for an arbitrary inhomogeneous medium all parts of which are at rest and in Ref. [9] to obtain the van der Waals friction to 1