Gabriel Popkin in Nautilus (Left photo by Gregory MD; right photo by De Agostini Picture Library):
I’ve never seen the computer you’re reading this story on, but I can tell you a lot about it. It runs on electricity. It uses binary logic to carry out programmed instructions. It shuttles information using materials known as semiconductors. Its brains are built on integrated circuit chips packed with tiny switches known as transistors.
In the nearly 70 years since the first modern digital computer was built, the above specs have become all but synonymous with computing. But they need not be. A computer is defined not by a particular set of hardware, but by being able to take information as input; to change, or “process,” the information in some controllable way; and to deliver new information as output. This information and the hardware that processes it can take an almost endless variety of physical forms. Over nearly two centuries, scientists and engineers have experimented with designs that use mechanical gears, chemical reactions, fluid flows, light, DNA, living cells, and synthetic cells.
Such now-unconventional means of computation collectively form the intuitively named realm of, well, unconventional computing. One expert has defined it as the study of “things which are already well forgotten or not discovered yet.” It is thus a field both anachronistic and ahead of its time.
But given the astounding success of conventional computing, which is now supported by a massive manufacturing industry, why study unconventional computing techniques at all? The answer, researchers say, is that one or more of these techniques could become conventional, in the not-so-distant future. Moore’s Law, which states that the number of transistors that can be squeezed onto a semiconductor chip of a given size doubles roughly every two years, has held true since the mid 1960s, but past progress is no guarantee of future success: Further attempts at miniaturization will soon run into the hard barrier of quantum physics, as transistors get so small they can no longer be made out of conventional materials. At that point, which could be no more than a decade away, new ideas will be needed.
So which unconventional technique will run our computers, phones, cars, and washing machines in the future? Here are a few possibilities.
A chemical reaction seems a natural paradigm for computation: It has inputs (reactants) and outputs (products), and some sort of processing happens during the reaction itself. While many reactions proceed in one direction only, limiting their potential as computers (which generally need to run programs again and again), Russian scientists Boris Belousov and Anatoly Zhabotinsky discovered in the 1950s and ’60s a class of chemical reactions, dubbed “BZ reactions,” that oscillate in time.