[**Entropy**](https://en.wikipedia.org/wiki/Entropy_(computing))

Computer programs are deterministic: given the same input, they'll produce the same output. Even pseudorandom generators are perfectly predictable, and hence utterly *boring*.

The solution is to ingest a little entropy every now and then: arbitrary bits drawn from some chaotic, unpredictable process. Entropy makes our crypto keys unguessable, lets us re-seed our [PRNGs](https://en.wikipedia.org/wiki/Pseudorandom_number_generator), lifts our [SGDs](https://en.wikipedia.org/wiki/Stochastic_gradient_descent) from their local minima, and reinvigorates the topiary of our [MCTS](https://en.wikipedia.org/wiki/Monte_Carlo_tree_search). We can revisit old data with fresh eyes, to spot new patterns; and, crucially, we gain some resilience against pathological/adversarial inputs.

There are many sources of entropy, depending on taste. Some make do with a slow trickle from the lower bits of the system clock; others indulge from the firehose of a dedicated metastable quantum oscillator circuit. The truly paranoid insist that all internal sources are suspect; it's not uncommon for the radio telescope task queue to be filled up to 20% with their patient observations of distant pulsars.