McCarthy - Hacking matter: levitating chairs, quantum mirages, and the infinite weirdness of programmable atoms

THE FLICK OF A SWITCH: a wall becomes a window becomes a hologram generator. Any chair becomes a hypercomputer, any rooftop a power or waste treatment plant. We scarcely notice; programmable matter pervades our homes, our workplaces, our vehicles and environments. There isnt a city on Earthor Mars, for that matterthat isnt clothed in the stuff from head to toe. But though we rarely stop to consider it, the bones of these citiestheir streets, their sewers, the hearts of their telecom networkswere laid out during a time when the properties of matter were dictated exclusively by Mother Nature.

Just imagine: if specific mechanical or electrical properties were desired, one first had to hire miners to extract appropriate elements from the Earth, then chemists and metallurgists to mix precise proportions under precise conditions, then artisans to craft the resulting materials into components, and assemble the components into products that could then be transported to the location of desired use. The inconvenience must have been staggering.

In the twenty-second century, of course, any competent designer will simply define the shape and properties she requiresincluding unnatural traits like superreflectance, refraction matching (invisibility), and electromagnetically reinforced atomic bondsand then distribute the configuration file to any interested users. But prior to the invention of wellstone the earliest form of programmable matterthis would have sounded like pure fantasy. With that in mind, well look back on the invention upon which, arguably, our entire modern civilization rests.

Consider silicon, whose oxide is the primary component of rockliterally the commonest material on Earth. Humans had been making hammers and axes and millstones out of it for millions of years, but as it happens, silicon is also a semiconductora material capable of conducting electrons only within a narrow energy band.

While silicon was invaluable in the development of twentieth-century digital electronics, its killer app eventually proved to be as a storage medium for electrons. When layered in particular ways, doped silica can trap conduction electrons in a membrane so thin that, from one face to the other, their behavior as tiny quantum wave packets takes precedence over their behavior as particles. This structure is called a quantum well. From there, confining the electrons along a second dimension produces a quantum wire, and finally, with three dimensions, a quantum dot.

The unique trait of a quantum dot, as opposed to any other electronic component, is that the electrons trapped in it will arrange themselves as though they were part of an atom, even though theres no atomic nucleus for them to surround. Which atom they emulate depends on the number of electrons and the exact geometry of the wells that confine them, and in fact where a normal atom is spherical, such designer atoms can be fashioned into cubes or tetrahedrons or any other shape, and filled with vastly more electrons than any real nucleus could support, to produce atoms with properties that simply dont occur in nature.

Significantly, the quantum dots neednt be part of the physical structure of the semiconductor; they can be maintained just beneath the surface through a careful balancing of electrical charges. In fact, this is the preferred method, since it permits the dots characteristics to be adjusted without any physical modification of the substrate.

Who invented wellstone remains a matter of confusion and debate; similar work was being performed in parallel, in laboratories all over the world. But regardless of where the idea originated, the concept itself is deceptively simple: a lattice of crystalline silicon, superfine threads much thinner than a human hair, crisscrossing to form a translucent structure with roughly the density of polyethylene. Wellstone behaves fundamentally as a semiconductor, except that with the application of electrical currents, its structure can be filled with atoms of any desired species, producing a virtual substance with the mass of diffuse silicon, but with the chemical, physical, and electrical properties of some new, hybrid material.

Wellstone iron, for example, is weaker than its natural counterpart, less conductive and ferromagnetic, basically less iron-like, and if you bash it over and over with a golf club it will gradually lose any resemblance to iron, reverting instead to shattered silicon and empty space. On the other hand, its feather-light, wholly rustproof, and changeable at the flick of a bit into zinc, rubidium, or even otherwise-impossible substances like impervium, the toughest superreflector known.

Of the changes wrought by programmable matter in the past one hundred years, not all have been universally welcomed. In the grand Promethean tradition, wellstone places the power of creation and destruction squarely in human hands. Many have argued that far from making us strong, this power fosters a quiet corruption of spirit. Still, the fable of the three little pigs holds true: not even the Luddites among us build their houses of straw or sticks when impervium is a free download.