Fairy-Tale Physics 2: Spinning Gold

You might think that Monday’s discourse on thermodynamics in the Goldilocks story was the only children’s story in which physics plays a role, but that’s not true. Physics is everywhere in fairy tales.

Take, for example, the story of Rumpelstiltskin, in which a mysterious little man demands a terrible price for helping a miller’s daughter spin straw into gold. This raises the obvious question of exactly how one would go about extracting gold from straw.

The use of the term “spin” might suggest the use of rotational motion– if the straw were ground up very fine, and mixed with water, it might be possible to use a centrifuge to sift out the trace amounts of gold that might be present in the straw. This would perhaps explain the need for whole rooms full of straw– the heavy metal content of most plants is minuscule, and so vast quantities of raw material would be required to produce a tiny amount of gold.

The sheer amount of wastage in this process, though, suggests that some alternate method must be employed. The next obvious choice would be to turn to nuclear reactions.

One might suspect that the mysterious little man was using some highly advanced nuclear reactions to convert the nuclei of the atoms in the straw into atoms of gold, perhaps through nuclear fusion. Straw is mostly carbon, and you might imagine a process whereby thirteen or so carbon nuclei were stuck together to produce a single atom of gold. This would still amount to a substantial reduction in the overall volume of material produced, requiring large rooms full of large material, but the gold yield would, in principle, be substantially higher.

This scheme, promising as it might seem, runs afoul of physics. As is well known to everybody but the people who write fairy tales, the nuclear binding energy curve reaches a maximum in the vicinity of iron. You cannot create elements heavier than iron through sustainable fusion reactions. While you might conceivably be able to fuse a few carbon nuclei into iron, getting from iron to gold would require a colossal amount of energy input, something well beyond the resources of a medieval-level society. The existing heavy elements in the universe are believed to have been produced in supernovae, which would tend to have a negative impact of the property values of any kingdom foolish enough to attempt this method of producing gold.

The peak of the binding energy curve does suggest a solution, though. While it would be impossible to fuse carbon into gold, you can use carbon nuclei to make iron and sulfur, and iron and sulfur are the main components of pyrite, also known as “fool’s gold.” Producing fool’s gold from straw is only barely less impressive than producing real gold from straw, particularly in an agrarian society with low rates of scientific literacy. And passing off fool’s gold as gold would be entirely consistent with the bad reputation of mysterious little men who make outrageous demands in fairy stories– they are most emphatically not to be trusted, and their gold often turns out to be worthless trash.

So, there you have a physically consistent explanation of the Rumpelstiltskin tale: the mysterious little man is clearly an alien from a more technologically advanced species, using sophisticated control of nuclear reactions to convert carbon-based plant matter into pyrite, and passing it off as gold in an attempt to obtain human children for biological experimentation and possible cross-breeding.

It all makes sense, now…