Hadronic collisions: physics, models and event generators used for simulating the cosmic ray cascade at the highest energies

Most hadronic event generators which can be used for simulating hadronic and nuclear collisions up to the highest energies are quite similar in their construction and in the underlying theoretical concepts. At energies, where data from accelerator and collider experiments are available the models agree rather well with each other and with the most important features of the data. As soon as we compare the extrapolations of the models at higher energy we find in spite of the similarities in the underlying theoretical concepts quite often striking differences between the predictions of the models.