Can one extract source radii from transport theories?
  To know the space time evolution of a heavy ion reaction is of great interest, especially in cases where the measured spectra do not allow to ascertain the underlying reaction mechanism. In recent times it became popular to believe that the comparison of Hanbury-Brown Twiss correlation functions obtained from classical or semiclassical transport theories, like Boltzmann Uehling Uhlenbeck (BUU), Quantum Molecular Dynamics (QMD), VENUS, RQMD or ARC, with experiments may provide this insight. It is the purpose of this article to show that this conjecture encounters serious problems. The models which are suited to be compared with the experiments at CERN and Brookhaven are not able to predict a correlation function. Any agreement with existing data has to be considered as accidental. The models suited for lower energies can in principle predict correlation functions. The systematic error may be too large to be of use as far as quantitative conclusions are concerned. 
J. Aichelin (SUBATECH, Univ. de Nantes, IN2P3/CNRS, EMN)