A comment on quantum-mechanical damping

The question of introducing damping into quantum mechanics has come into prominence again. It is argued, from previous experience with the damping of a harmonic oscillator, that it is easy to violate the uncertainty principle, particularly if it is overlooked that absorbers are also emitters. The usual classical equations for a damped system are those for a smoothed variable, with the noise fluctuations subtracted. In the case of a damped harmonic oscillator the process of subtracting the noise and so defining a smoothed variable was examined many years ago, and to some extent can be used to justify present practice.