Crab computing: building a biological machine

In layman’s terms, the researchers were trying to show the behavior one would expect from a logical gate (AND, OR, NOT), by using physical principles.

In an electronic circuit, the logic is "enforced" by using electricity, i.e.—either there is an electric current or there isn’t at one of the inputs of the logical gate.

The researchers wanted to see whether they could use simple physical processes (the bouncing around of billiard balls in some environment) as a way of applying the same logical gates in an electronic circuit.
The problem they discovered, however, is that this is energy inefficient, because of all the power lost making the gates work.

As a result, Fredkin and Toffoli used simple physical processes (the bouncing around of billiard balls in some environment) as a way of applying the same logical gates in an electronic circuit.

If one were to imagine a pool table, with all sorts of small walls arranged on it, sort of like a maze, with many entrances and exits, that arrangement would represent the "hardware" of the computer. The logical gates.

The "software" is represented by the billiard balls, placed at some of the entrances, and then rolled into the maze with some velocity.

The combination of which entrances the billiard balls are put into, and the arrangement of the walls on the table determines which ball rolls out at which exit from the maze.

And presto: you have the makings of a computer.

What’s extra cool about the whole thing is that it’s also reversible, so if one were to roll the balls that came out of the maze back into the exits they came out from at the same speed they exited, the exact same inputs would be achieved.

There is very little energy lost in such an idealized process, which  is a big deal, if one were to consider all the coal operated power plants it takes for Amazon, Facebook, Google and the likes to maintain electricity to keep their datacenters going.
Using the crab model
Getting back to the crabs, though, what the Japanese researchers did was to take the whole billiards concept to the next level, substituting balls for swarms of crustaceans which they claimed could “implement logical gates when placed in a geometrically constrained environment.”

Not just any kind of crab fits the experimental bill, however, with researchers opting for soldier crabs who swarm in packs, with the aggressive leaders forming a strong outline for the group, while the crabs in the middle hustle along in a kind of collective crush.

Researchers found that by putting a swarm of soldier crabs into a corridor, they would march along the wall in a similar way to the path of the billiard ball. Even better, because the crabs are biological organisms and respond deterministically to certain external stimuli, they could be easily controlled by the scientists, who experimented by casting shadows over the swarm from above, to simulate crab-eating birds. In the interest of self-preservation, the crabs instinctively moved away from those shadows.

Also, as various groups of soldier crabs bumped into each other, researchers noted that they seemed to merge before continuing on in the direction that was the sum of their respective velocities.

This is cool because it used the natural tendencies of crabs to run together as a group, or split apart from the group, as a kind of logical gate.

Since a logical gate is one of the fundamental parts of an electronic circuit, what the researchers actually managed to prove is that whatever can be done in an electronic circuit is also possible with large numbers of crabs. Which is kind of neat, if you think about it. Not a crabby idea at all.

Of course, it’s not the first instance of biology meeting computing. There’s "ant hill optimization," the mathematical trick to optimize algorithms, but simulating a whole computer out of little creatures really still puts the icing on the crab cake in my personal opinion.

And who knows, maybe it’s a real step towards a future biological-based real, working computer.
Imagine it: a computer whose computational units are based on living matter, or organic molecules. No electricity required, just some food substrate.

Maybe it’s a step toward a biological-based computer.

If scientists found a way to actually make that happen, it might even come to embody the old Douglas Adams notion of the the entire earth being a huge computer, designed  by an alien race to calculate the answer to life, the universe, and everything.

Although, we already know that the answer to that is 42.