Answer: Heisenbug

If familiar with quantum mechanics (even if you’re just an armchair dabbler), then you likely not only honed right in on today’s trivia answer, but appreciated the pun packed within. In physics, there is a concept known as the “observer effect” that states that simply observing or measuring a phenomenon changes that phenomenon in some way. While, on a macro level, most observations do not fundamentally change the nature of an experiment or measurement in any practical way, when we get down into the very micro landscape of quantum mechanics, there is a particularly vexing example of the observer effect wherein simply observing the state of a quantum phenomenon can change the state of the phenomenon.

This quantum-level observer effect was first asserted by famed physicist Werner Heisenberg (perhaps best known for the related but different Heisenberg uncertainty principle), and the term “heisenbug” is a tongue-in-cheek portmanteau of his name and “computer bug”. Such bugs seem to disappear or alter their behavior based on whether or not they are observed. They occur in programming because there are numerous variables at play (both literally in the actual code, and more broadly in terms of things like the load on the system during different points of debugging and testing) and the process of debugging often, unwittingly, alters said variables. There is a related term on the hardware/electronics side of things known as the “probe effect”, wherein using a probe to monitor the system creates a change that alters the outcome of the observation and troubleshooting session.