Some consequences of the nonlocalizability of space-time events

Space-time events are characterized by their coordinatesx from the classical point of view. The same events from the quantum-mechanical point of view should be described rather by the expectation value of coordinates X. The expectation value could be evaluated by introducing a density operator(x,x) associated with the event. In the case where(x,x) cannot be described by delta functions strictly monochromatic radiation does not exist. If localizability is limited by Planck's length there are no narrower spectral lines than 2× 10^–29E² (eV) whereE stands for the photon energy.On leave from the Institute of Nuclear Physics, Kraków, ul. Radzikowskiego 152, Poland.