Ultra-high-energy cosmic rays (UHECRs) are extremely energetic particles originating from outer space that strike Earth with energies exceeding \(10^{18}\) electron volts (eV). To put this into perspective, these energies are several orders of magnitude greater than those produced in the most powerful man-made particle accelerators on Earth. UHECRs are primarily composed of protons, although they can also include heavier nuclei and possibly other types of particles.
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Sometimes it feels like this could be how we finally make experiments to see what the theory of everything looks like, a bit like the first high energy experiments were from less exotic cosmic rays.