Classical limit of mechanical thermal noise reduction by feedback

This is the authors' abstract. We don't add key points for this paper.

The classical theory of thermal noise of mechanical systems and the effects of feedback is reinvestigated. Previous developments which set a limit to the noise reduction by feedback when a given measuring time is assumed have ignored the situation where the system is acting as an unchanging mechanical reference. A precision rotor clock is one such system. The present work uses the galvanometer as the general model and includes this situation. It explicates the nature of the limit when it exists by treating it without assuming any particular measuring optimization method.