On St. Patrick’s Day, the most well-known creatures of Irish folklore–the small, tricksterish, dapper-dressed leprechauns–come out of the woodwork. The distorted pop culture image of the leprechaun, with his all-green outfit, red beard, and ridiculous buckled hat, can be seen year-round in association with certain beloved breakfast cereals and sports teams, but a magical humanoid fairy creature couldn’t exist in real life. Or could it? Turns out, some of the aspects of the leprechaun legend have some scientific–or at least theoretical–basis:
The Gold: Pyrite
The most common trick leprechauns are seen to play on humans is the old crumbling-gold scam. The story goes that the leprechaun stashes a cauldron full of gold coins at the end of a rainbow and waits for some greedy individual to steal it. By the time the enterprising burglar gets it all home, it’s crumbled into dust, worthless. The pure substance we call gold–Au, that is–wouldn’t undergo this transformation. It’s chemically stable and can’t be dissolved in the majority of acids, and doesn’t corrode. The mineral iron pyrite, alias fool’s gold, however, resembles true gold in every superficial aspect save that it forms in cubic crystal lattices. Unlike malleable and stable gold, pyrite is incredibly brittle and incredibly unstable. If the leprechaun had a sufficiently hard chisel, he could shape pyrite into coins, which would rapidly decompose with the water vapor in air into iron oxides and sulfate; rust powder, in common terms.
The Fast Labor: Time Dilation
When not pulling moralistic pranks, leprechauns are usually depicted as industrious cobblers, working on shoes at unholy speed and cranking out an entire storehouse full of them in a night. The “magical” explanation is that the leprechaun simply has supernatural levels of stamina and dexterity. However, physics provides a means by which the leprechaun could work at what it perceives as a normal pace and still have what relativistically speaking is much greater productivity than the time would allow. A very, very dense leprechaun–small in its dimensions but still with a huge mass–would have a strong gravitational field. Such a leprechaun would be subject to gravitational time dilation, a phenomenon whereby clocks run slower the closer they are to massive objects, meaning that due to gravity’s little-understood effects on the space-time continuum, actual perceived time slows down. The leprechaun, therefore, would have all the time in the world whilst outside only one night passed.
The Luck: Many-Universes Discontinuity
Leprechauns are supposed to have improbably good fortune to such a degree that the most well-known one in pop culture is literally named Lucky. We could accept that leprechauns warp the laws of probability by vague magical means, but it takes a lot of leaps of logic to say that “when a leprechaun is involved, random events are suddenly much less random.” Quantum physics has a better answer which starts with a deeply unlucky cat. Schrödinger’s cat is a well-known thought experiment wherein the said cat is kept in a sealed box with a Geiger counter, a tiny amount of radioactive substance, and a phial of instantly lethal poison. Over a given period of time, whether the substance will undergo radioactive decay or not is unpredictable. If it does, the Geiger counter triggers the phial to break, killing the cat with the poison. If not, the cat stays alive. After the time period, until the box is opened, the cat can be said to be both alive and dead at once; opening the box collapses the quantum state and makes the cat either only alive or only dead. That is, of course, assuming there’s a single linear spacetime. The many-worlds hypothesis says when such a quantum state scenario is created, both events definitively do happen, but in different realities, even though the observer can only experience one at one time. If the leprechaun is capable of not perceiving time linearly, he effectively has his choice of outcomes of supposedly random events, which is why you should not make a wager with one.