ABSTRACT

It is not extremely difficult to accept the fact that a signal can't be "localized" simultaneously in time and in frequency. Speaking of a frequency at a given instant doesn't really have a meaning; a frequency has to have the time to oscillate. It is much harder to come to terms with the fact that one cannot speak of an elementary particle's precise position and precise momentum. One may be tempted to think that Heisenberg imposes a limit on what one can know (lacking the necessary intelligence or tools). That is not the case. As in signal processing, the Heisenberg principle describes a reality: an elementary particle does not have simultaneously a precise position and a precise momentum.