Some consequences of the nonlocalizability of space-time events

Space-time events are characterized by their coordinates x 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 . The expectation value could be evaluated by introducing a density operator rho(x,x') associated with the event. In the case where rho(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 approximately 2X10-29 E2(eV) where E stands for the photon energy. (author)