The GZK Limit & Cosmic Ray Paradox | Special Relativity

In this video, we will discuss the GZK limit, which is an upper limit for the energy of cosmic rays coming from far away sources. It is named after those three physicists, who calculated this cutoff energy in 1966.

In short, this energy limit is due to collisions of cosmic rays, that is protons, with photons from the cosmic microwave background radiation. Even if there are some very high energy protons far away coming towards us, they will collide with CMB photons and produce pions. This reduces the proton energy by around 20% and this reduction of the kinetic energy happens until some specific energy is reached. This means that protons below the GZK energy limit can reach us, but those with higher energies lose their energy again by making pions along the way.

Contents:
00:00 Introduction
00:56 Reaction process & determining the energy

02:51 More accurate result

03:29 GZK paradox


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