2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/212908We do not have the ability to perform precise calculations of long-range strong interaction effects, because the effective QCD coupling is not small and so we cannot use perturbation theory. Nevertheless, I show that we know a lot, though not nearly enough. As a measure of our lack of knowledge, the best prediction for the total cross section at LHC energy is 125 +/- 25 mb.Lectures at School on QCD, Calabria, July 2007High Energy Physics - PhenomenologyHigh Energy Physics - Experimenttext