# Computers are vulnerable against cosmic rays Transistors make up all of the world's computers. In particular, they can be used to store information by remaining in a given binary state (0 or 1). The memory of a computer is therefore linked to the physical state of the transistors in a two-way relationship. Usually, it is the software that dictates the state of the hardware: as I save this note, the states of some transistors are updated to reflect the state of the note. However, transistors are not completely isolated from the rest of the world: among other things, their states can be switched (in what are called *bit flips*) if they are hit by an energised particle. This can be caused by natural radioactive activity or by cosmic rays, which are waves of particles emitted by supernovae and black holes. While modern circuits are made resilient against bit flips, we can simply not prevent them. Furthermore, they are *soft* errors: they leave no trace. Our only means of defense against bit flips is to redundant information, *ie*, backups. --- ## 📚 References - [[@veritasiumUniverseHostileComputers2021|The Universe is Hostile to Computers]]