Back in the 1980s two computer scientists, Edward Fredkin and Tommaso Toffoli, proposed making a computer using billiard balls. The point was to investigate the relationship between reversible processes in physics and computation. The billiard balls would be fed into a logic circuit, and the output would depend on them colliding with each other.
That's where the crabs came in. Gunji and Nishiyama decided to use the crustaceans in place of the billiard balls. One reason was that when two swarms of crabs collide, they keep going in a direction that is the sum of their velocities, just as billiard balls do. They used groups of 40 crabs to make a swarm.
To test the idea the two scientists built logic gates, which are the tracks the crabs can move in. One is an OR gate, which gives a result of 1 of either or both inputs are 1. The other is an AND gate, which returns a 1 only if both inputs are also 1.
The "switch" to get the crabs moving was simply putting a shadow above them, because soldier crabs are eaten primarily by birds, and when they see a shadow, they start moving.
The OR gate was easier, as it turned out, because it just involved two swarms of crabs merging into one. AND was tougher to make work, because the crabs had to go down one of three paths. But the researchers say they might be able to make it more successful if they make the environment better for the crabs.
The team published their results on the arXiv website.
NEWS: DNA Computer Gets Scaled Up
So does this mean that we'll be seeing a crab-powered computer? Odds are no, as the entire thing would have to be enormous. But the experiment offers some insight into the behavior of both swarming systems and computers.
Gunji and Nishiyama noted that the crabs were unharmed during the experiment, and they were all returned to their respective habitats.
Top photo: Soldier crabs of the species Mictyris longicarpus, an Australian variety.
via New Scientist
Bottom photo: Wikimedia Commons / Peter Ellis