Hydrodynamic fluctuation forces
Two interaction mechanisms of particles in a fluid are proposed on base of forces, mediated by hydrodynamic thermal fluctuations. The first one is similar to the conventional van der Waals interaction, but instead of been mediated by electromagnetic fluctuations, it is mediated by fluctuations of hydrodynamic sound waves. The second one is due to a thermal drift of particles to the region with a bigger effective mass, which is formed by the involved surrounding fluid and depends on an inter-particle distance. The both mechanisms likely can be relevant in interpretation of the observed long-range attraction of colloidal particles, since a set different experiments shows the attraction energy of the order of kT and, perhaps, only a fluctuation mechanism of attarction provides this universality.