 Bohmian mechanics is the minimal completion of Schrödinger’s equation, for a nonrelativistic system of particles, to a theory describing a genuine motion of particles. For Bohmian mechanics the state of a system of \(N\) particles is described by its wave function \(\psi = \psi(\boldsymbol{q}_1 ,\ldots ,\boldsymbol{q}_N) = \psi(q)\), a complex (or spinor-valued) function on the space of possible configurations \(q\) of the system, together with its actual configuration \(Q\) defined by the actual positions \(\mathbf{Q}_1 ,\ldots ,\mathbf{Q}_N\) of its particles. (The word “spinor” refers to a suitable array of complex numbers in place of a single one. Spinor-valued wave functions are used in quantum mechanics to describe electrons and other quantum particles that “have spin”.) The theory is then defined by two evolution equations: Schrödinger’s equation   \[ i\hslash\frac{\partial \psi}{\partial t} = H\psi \]   for \(\psi(t)\), where \(H\) is the nonrelativistic (Schrödinger) Hamiltonian, containing the masses of the particles and a potential energy term, and (writing \(\Im[z]\) for the imaginary part \(b\) of a complex number \(z = a +\di b)\) a first-order evolution equation, 