This is what happens: https://en.m.wikipedia.org/wiki/Greisen–Zatsepin–Kuzmin_limit https://en.m.wikipedia.org/wiki/Greisen–Zatsepin–Kuzmin_limi... To the seco

This is what happens: https://en.m.wikipedia.org/wiki/Greisen–Zatsepin–Kuzmin_limit https://en.m.wikipedia.org/wiki/Greisen–Zatsepin–Kuzmin_limi... To the second question: it loses energy due to pair creation (iirc, surely simplifying due to bad memory).