Comment by DonHopkins

Reversible Computing (2016) [video] (youtube.com)

https://news.ycombinator.com/item?id=16007128

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

DonHopkins on Dec 26, 2017 | next [–]

Billiard Ball cellular automata, proposed and studied by Edward Fredkin and Tommaso Toffoli, are one interesting type of reversible computer. The Ising spin model of ferromagnetism is another reversible cellular automata technique. https://en.wikipedia.org/wiki/Billiard-ball_computer

https://en.wikipedia.org/wiki/Reversible_cellular_automaton

https://en.wikipedia.org/wiki/Ising_model

If billiard balls aren't creepy enough for you, live soldier crabs of the species Mictyris guinotae can be used in place of the billiard balls.

https://www.newscientist.com/blogs/onepercent/2012/04/resear...

https://www.wired.com/2012/04/soldier-crabs/

http://www.complex-systems.com/abstracts/v20_i02_a02.html

Robust Soldier Crab Ball Gate

Yukio-Pegio Gunji, Yuta Nishiyama. Department of Earth and Planetary Sciences, Kobe University, Kobe 657-8501, Japan.

Andrew Adamatzky. Unconventional Computing Centre. University of the West of England, Bristol, United Kingdom.

Abstract

Soldier crabs Mictyris guinotae exhibit pronounced swarming behavior. Swarms of the crabs are tolerant of perturbations. In computer models and laboratory experiments we demonstrate that swarms of soldier crabs can implement logical gates when placed in a geometrically constrained environment.