Abstract The lattice Boltzmann concepts and applications described so far refer to classical (non-quantum) physics. Whether this limitation is strictly scientific or purely contingental in character, it is difficult to say. However, it appears plausible to speculate that at least part of the LBE assets should be exportable to the quantum world. In principle, this does not even require much of a conceptual jump, since it has been known for a long time that quantum mechanics can be formulated in a fluid dynamic language. This analogy is precisely the stepping stone for this final chapter: stay with us, LBE goes quantum mechanical! Intriguing analogies between quantum mechanics and fluid mechanics have been pointed out since the earliest days of quantum theory [212]. The orthodox tenet is that these analogies are purely formal in character and do not bear upon the basic physics of quantum phenomena. A less orthodox, albeit not minor, stream of thought insists instead that quantum mechanics and notably its philosophical hard-core, Heisenberg’s uncertainty principle, are nothing but a mirror of our ignorance of the underlying (hidden) microscopic physical level. This leads to the puzzling theory of ‘hidden variables’ which can be traced back to Einstein and subsequently to D. Bohm and others [213]. It is not our intention here to enter this fascinating and still open subject [214]. We turn to a practical question instead: what can the analogy do for us in terms of numerical modeling of evolutionary quantum mechanical phenomena? The question is legitimate because, regardless of its philosophical implications, the fluid analogy certainly provides an intuitive and sound basis to develop numerical methods for time-dependent quantum mechanics. In particular, it appears reasonable to ask whether the advantages brought about by LBE in fluid dynamics can (by means of the fluid analogy) be exported to the context of quantum mechanics. Before we put forward our discrete kinetic theory version of the analogy, it is useful to provide a cursory survey of the main ideas behind the analogy itself. To this end, a short recap of basic notions of quantum mechanics is in order.
We describe a series of experimental analogies between fluid mechanics and quantum mechanics recently discovered by a team of physicists. These analogies arise in droplet systems guided by a surface (or pilot) wave. We argue that these experimental facts put ancient theoretical work by Madelung on the analogy between fluid and quantum mechanics into new light. After re-deriving Madelung’s result starting from two basic fluid mechanical equations (the Navier–Stokes equation and the continuity equation), we discuss the relation with the de Broglie–Bohm theory. This allows to make a direct link with the droplet experiments. It is argued that the fluid mechanical interpretation of quantum mechanics, if it can be extended to the general N-particle case, would have a considerable advantage over the Bohm interpretation: it could rid Bohm’s theory of its non-local character.