Connections between newton‐ and schrödinger‐type equations in the description of reversible and irreversible dynamics

Taking into account wave‐particle duality and the uncertainty principle, a nonlinear Schrödinger wave equation (NLSE) for the description of dissipative systems can be constructed by applying only Newton's form of classical mechanics. A comparison between our NLSE for dissipative systems and the linear time‐dependent SE for conservative systems shows that, for free motion and motion in a harmonic potential, both equations have Gaussian wave‐packet solutions. The time dependence of the maximum of these functions is governed by the classical (real) Newtonian equation of motion. While the time dependence of the width of the wave packet can be determined from a nonlinear complex Bernoulli/Ricatti type differential equation. This can be done by transformation into a Newton‐type equation for a real quantity α (which is proportional to the square root of the width), including a kind of “centrifugal force” term. This equation can be solved analytically and when taken with Newton's equation of motion for the mean value of the position, it forms a so‐called Ermakov system. For the linear SE equation, this implies the existence of a dynamical invariant. For our NLSE we also obtain such an exact invariant, but now for a dissipative system. Furthermore, this complex nonlinear equation can be linearised using the logarithmic derivative of a complex quantity λ, thus yielding a complex Newtonian equation of motion. The absolute value of λ is equivalent to α, the phase angle can be determined using a relation that connects real and imaginary parts of λ. This relation is linked to a kind of “conservation of angular momentum” for the quantity λ in a complex plane. The relations between the above‐mentioned quantities will be discussed in detail.