Villani used this poetical picture in order to describe some results about the Euler equation for an incompressible fluid: \[\frac{\partial v}{\partial t} + \nabla \cdot \left ( v \times v \right ) + \nabla p = f\] \[\nabla \cdot v = 0\] About this equation (or this sistem of wave equations), Scheffer (in 1993) found that the equation permit the spontaneous creation of energy form nothing, while Shnirelman (in 1997), found a new proof of this fact and proposed to enforce a criterion for physically prevent this kind of mathematical solutions. Sheffer and Shnirelman Theorem:
There is a weak solution of the Euler incompressible equation in 2-dimensions, without forcing ($f \equiv 0$) with compact support in space-time.Between 2007 and 2008 De Lellis and Szekelyhidi proofed a more general theorem that establishes, among other things, that the criterion of Shnirelman is not valid, or, in other world, that the solutions of the Euler incompressible equation without forcing are physically acceptable.