  We study space-time resolved densities of particle-hole pairs produced by an
external time-dependent field acting on non-interacting non-relativistic
particles. It is shown that, at least in some cases, the densities are not
affected by Fermi-Dirac or Bose- Einstein statistics, and are determined only
by the initial state of the multi-particle system. The second quantisation
technique is extended to Dirac electrons and, with some modifications, to
Klein-Gordon bosons. The difference in pair production in these two
relativistic cases is analysed in some detail.
