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Comment by neontomo | Hacker News Reader

I've been contemplating lately what types of everyday items could be used to create a simple calculator / full adder, outside of the digital realm. Something like candles would be interesting to experiment with. I haven't thought of how it would technically work yet, but if anyone has ideas please share.

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This is an interesting but niche topic. It’s called conservative logic[1] and is typically described via a pool/billiard “circuit.” The idea is that it’s more expensive but entirely reversible. I find myself wondering what simple bit possible computers primitive man could have come up with (had they dedicated themselves as much as e.g. the pyramid builders)

1. https://web.cecs.pdx.edu/~mperkows/temp/June16/ConservativeL...

Do you know of any specific examples I can look into where someone built a computer circuit out of normal objects?

Searching on “mechanical computers” may provide some things. Stuff could also have been done with water.

The main example is using billiard balls to act as a circuit (the benefit here is it’s entirely reversible.). It has not been done at scale

https://handwiki.org/wiki/Billiard-ball_computer

Overflowing water pools with barriers operated by level or flow in some other pool would be the intuitive candidate. Very close to popular mental models of electricity and people do like to have fountains around. Fountain/playground intermediates seem to be particularly popular.

It's been baffling me since late childhood that this isn't a thing everybody loved until they became "oh no, not another one of those!" frequent. Remember when fountains of that giant stone sphere slightly elevated by water pressure type weren't definitely not cool anymore yet?

To give use some ideas:

https://www.youtube.com/watch?v=IxXaizglscw

https://patents.google.com/patent/US3314439A/en

And maybe some inspiration:

https://archive.org/details/ExhalationByTedChiang

Toy model train sets can be Turing complete: http://www.cr31.co.uk/stagecast/trains/tt8_mech_logic.html

I also read a sci-fi book (forgot the title) that involved a pre -tech civilization that had invented computation, and executed code with large crowds of people standing in a grid following set rules to act as logic gates.

This is described, IIRC, in The Three-Body Problem[1]

[1]: https://en.wikipedia.org/wiki/The_Three-Body_Problem_(novel)

And more generally the concept is known as a China brain

Thank you, I suspected this is where I remembered it from, I had narrowed it down in my memory to either this book, or something from Vernor Vinge.

I wonder if one could turn crowds of humans into one, eg. engineering flash sales and other social cues they nudge them through gates.

as I mentioned in another reply to this, there is a popular sci-fi book that includes computation with crowds… surely someone on here will mention the title

Not exactly "everyday", but you can solve differential equations using pulleys and gears.

https://en.m.wikipedia.org/wiki/Mark_I_Fire_Control_Computer Is pretty cool analog computer

Well if you connect two candles together (“A” and “B”), that would make a NAND gate already, with lit being 0.

To connect two of these candle NAND gates together, you’d have to make sure it wouldn’t burn in reverse though. I’ll leave that exercise to the reader…

How do you imagine them being connected?

It's not clear how two lit inputs results in an unlit output or vice versa with that setup. How do you make that work?

Relevant xkcd: https://xkcd.com/505/

How do rocks give rise to qualia ?

In the comic, I believe the idea is that this entity is moving the rocks by hand, but following the rules of computing which slowly, but steadily, creates the world as a computer simulation. And in this case, the qualia would be an emergent property of that simulation, but how that happens or whether it happens at all is a much bigger debate...

How do atoms?

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