So basically, we have low level neutron radiation coming at us at all times from space. Mostly from our own sun, some other external sources too. It takes a whole lot of concrete or lead or water to stop that completely, so anything that makes it through our atmosphere is harmlessly passing through all of us.

But since things like computer RAM and other electronic storage have gotten so much smaller, this radiation is now capable of energizing or discharging individual bits — 1s or 0s — in that storage. Imagine you’re in the hospital for a back operation and the robot arm is approaching a 1 bit that tells it to stop… but that 1 flips to a 0 because the sun sneezed and now your spine is in two fun-sized pieces.

This is all mostly moot today, though. ECC-enabled RAM (memory with protections against bit flips) is the norm and this is a pretty well-understood problem.