Wouldn't your latest generation tablet be way cooler if it ran on live crabs? Thanks to Yukio-Pegio Gunji and his team at Japan’s Kobe University, the era of crab computing is upon us ... well, sort of. The scientists have exploited the natural behavior of soldier crabs to design and build logic gates - the most basic components of an analogue computer. They may not be as compact as more conventional computers, but crab computers are certainly much more fun to watch.
Electricity and microcircuits aren’t the only way to build a computer. In fact, electronic computers are a relatively recent invention. The first true computers of the 19th and early 20th centuries were built out of gears and cams and over the years many other computers have forsaken electronics for marbles, air, water, DNA molecules and even slime mold to crunch numbers. Compared to the slime mold, though, making a computer out of live crabs seems downright conservative.
The scientists at Kobe university didn’t just pop down to the market for their crabs. They focused their attention on a particular species: soldier crabs (Mictyris longicarpus). These are found in on the beaches of Australia and surrounding islands where they regularly provide visitors with surreal performances. Individually, the soldier crabs are timid little blue crustaceans that won’t even go into the water, but when they form into swarms, which can number in the tens of thousands, it’s a different matter.
Once set in motion by something like a bird’s shadow passing overhead, the soldier crabs tear off like an army of demented robots. They rush about in a strange, boiling mass that seem like exercises in utter chaos, yet the swarm itself moves in a remarkably consistent straight line. This determined, predictable manner of movement is the key to the crab computer.
When two swarms of soldier crabs collide something remarkable happens. Instead of collapsing into a riotous battle, the two swarms meet in a manner that’s as predictable as a pair of billiard balls hitting each other. When two identical billiard balls collide head on they, ideally and all things being equal, rebound off one another in the opposite direction. If they strike at an angle, they fly away from each other at the opposite angle. It’s all very predictable Newtonian mechanics. In the case of soldier crabs it’s like two balls of soft modelling clay hitting each other. They squash together at the new, larger swarm and head off at the combined angle of the original swarms with a remarkable degree of predictability.
Exploiting this behavior, the Kobe team figured out how to use the crabs to make logic gates. They did this by placing two swarms of crabs in a simple maze. In one configuration, the swarms were set off in two legs of the maze. When they collide, they head off down a third leg. Since the swarms always go in the same direction, if only one swarm is placed in the maze, it will always go down the same output leg as if it had collided with the other swarm and not double back up the other leg. In this way, the maze becomes an OR gate. If one or two swarms enter the maze, the output is always positive. One swarm OR another swarm in the maze equals a positive, otherwise negative.
The researchers also used another maze was in the shape of an X with a fifth vertical leg stuck running up from the center. In this maze, letting loose one swarm resulted in the swarm passing straight through the center and into the opposite leg of the X. If two two swarms are loosed, they collide in the center, sending them up through the center leg. This is the crab equivalent of an AND gate. One swarm going in provides a negative. Two provides a positive. One swarm AND another swarm equals positive, otherwise negative.
With these two gates, it would be theoretically possible to build more complicated logic gates and from there, full-fledged computers.
Currently, there are no plans to build a full-blown crab computer, but if seafood cybernetics ever does take off, this, they will say, it where it all began.
The research was recently outlined in a paper entitled Robust Soldier Crab Ball Gate [PDF] in the journal Complex Systems