# How might a clockwork mechanism be built, to behave in a pseudo-random or chaotic way?

My brother asked me how I might build a functioning alethiometer, which is a fictional device superficially resembling an analog pocket watch, but with essentially random movements. I told him I would use electronics rather than clockwork ("clockwork" is colloquially synonymous with predictable mechanical motion, after all). But that didn't stop me from wondering how it might be done in a purely mechanical way.

A larger, immobile device might combine a pendulum clock with a chaotic double pendulum system, for example. What other mechanical randomness source might work for a smaller, portable device?

• This is an interesting question and has me thinking. My first thoughts are that it would require some external "noise" such as temperature fluctuations, wind, solar, tidal, rain, volcanic or other natural phenomena to provide some variation. Let's see what comes up. Mar 14, 2021 at 21:33
• I'm also curious about a pseudorandom solution. Perhaps something like a series of oddly-shaped cams with relatively prime periods? I'm not sure what would be a reasonable way to construct something like that. Mar 15, 2021 at 3:59
• There is a 2012 paper titled "Chaos in coupled clocks" which leads me to believe that it might be possible to build two watches with mainsprings, coupled in a way somehow analogous to coupled pendulums. Also, it strikes me that the Antikythera mechanism exhibits what looks like pseudorandom behavior, if you aren't aware of what it represents. Mar 15, 2021 at 4:12
• @monguin I agree - that was my first thought, to couple one hairspring to another. (Not the mainspring; that's just the power source). That at least gives you a random elapsed "real time" per ratchet step. randomizing forward/backward would be more tricky. Mar 15, 2021 at 12:18
• There's a very interesting experiment (magnetic pendulum) you could look into. You take some magnets and fix them to a table. Then swing a pendulum (iron mass) and wait to see at which magnet it stops. No matter where you start the pendulum, you cannot predict where it will stop. Maybe that could give you some ideas? Mar 16, 2021 at 12:42