Somehow, you have to like a paper which contains the phrase
Now, let us assume that the effective cross section for the inelastic scattering of two cosmic rays is of the size of the Universe.
Cosmic rays are tiny things - mostly protons, or atomic nuclei - travelling through space, so the idea that they might in any sense become as big as the universe is an odd one. Actually the idea of anything apart from the universe being as big as the universe is disturbing. If your theory predicts this is happening, you might be tempted to junk it and get a new theory.
Of course, that is the point. The paper in question is another attempt at ‘reductio ad absurdum’ on the Standard Model of particle physics; part of an attempt to find out how high in energy we might have to go before the model breaks.
As we increase the energy of our accelerators, we can look at smaller and smaller structures of matter. It is a bit like being given access to more landscape to explore, extending the map of physics into terra incognita at tiny distances.
Physics is in an interesting position, now that the Higgs boson has been discovered. The “Standard Model” doesn’t predict any more new particles, no matter how tiny, and it could be considered internally complete. However, it is very far from being a theory of everything, failing to account for such major experimental facts as gravity, the different amounts of matter and antimatter in the universe, and the 85% or so of stuff that seems to be “Dark Matter”. It also struggles with neutrinos