"Rappers" on the roof of the electrostatic precipitator knock the accumulated dust free, letting it fall into the storage hopper. Each rapper is the size and shape of a baseball bat. Inside is an electromagnet that pulls a steel plunger upward, then allows it to fall again, producing a sharp knock. The rappers are energized at seemingly random intervals, producing a haunting, syncopated music. (The rhythm seemed more modern jazz than rap.)
Today population forecasts are based on extensive and reliable data. However, no such demographic base exists for the world's growing population of machines and devices. Now may be the time to take machine demography seriously and enter into real discussions about machine population control.
The couple of years in question here saw one of the largest bureaucracies anywhere undergo a convulsion in which it tried to reconceive itself as a non- or even anti-bureaucracy, which at first might sound like nothing more than an amusing bit of bureaucratic folly. In fact, it was frightening; it was a little like watching an enormous machine come to consciousness and start trying to think and feel like a real human.
Wang tiles (Hao Wang, 1961) are a class of formal systems. They are modelled visually by square tiles with a color on each side. A set of such tiles is selected, and copies of the tiles are arranged side by side with matching colors, without rotating or reflecting them.
The basic question about a set of Wang tiles is whether it can tile the plane or not, i.e., whether an entire infinite plane can be filled this way. The next question is whether this can be done in a periodic pattern.
In 1966, Wang's student Robert Berger solved the problem in the negative. He proved that no algorithm for the problem can exist, by showing how to translate any Turing machine into a set of Wang tiles that tiles the plane if and only if the Turing machine does not halt. The undecidability of the halting problem then implies the undecidability of Wang's tiling problem.