Ask Ethan: How much damage could a cosmic ray do to a human?

"Here in our isolated corner of the Universe, we don't normally think about all the objects, particles, and photons that miss us, even though we know they're ubiquitous out there. Instead, all that we observe are the ones that arrive here: on Earth, in our detectors, in our telescopes, and even in our eyes. There are plenty of objects out there whose light is on the way, but hasn't reached us just yet: objects beyond our current cosmic horizon, but not our future visibility limit."

"Back in 1991, the Fly's Eye camera in Utah detected what was, at the time, a uniquely energetic event: a signature of an ultra-high-energy cosmic ray that was so far above the theoretical maximum, it created a mystery that lasted for decades. Known ever since as the Oh-My-God particle, it remains the highest-energy particle event ever observed, but has since been joined by many comparable ones."

Many high-energy particles and photons travel through space without reaching Earth, and only those that arrive can be observed. Massive astrophysical engines such as black holes and neutron stars accelerate particles to energies far beyond terrestrial capabilities. Such ultra-high-energy particles rarely interact with Earth and produce observable signatures. A 1991 Fly's Eye detection recorded an ultra-high-energy cosmic ray, dubbed the Oh-My-God particle, the highest-energy event observed and far above theoretical expectations. Even the most energetic cosmic rays deposit their energy over tiny regions and through interactions with the atmosphere, so direct impact on a human would cause negligible harm.

Read at Big Think