Will-o'-the-wisps: The mystery of the blue lights solved

Alessandro VoltaIn 1776, he had a hunch. The will-o'-the-wisps, those blue flames that danced over the marshes at night, he said, must have something to do with electricity. Then came methane, phosphine, and theories about marsh gas. But there was always one piece missing: who lights the fuse? Now a team of Stanford chemists has filmed the answer with high-speed cameras.

It happens in less than a millisecond, between two bubbles touching in the water. A spark. Not as big as lightning, but enough to make methane react with oxygen. No heat, no real flame. Just cold, blue-purple light, floating in the air like a ghost. Will-o'-the-wisps aren't lost souls. They're micro-lightning bolts. And they change the way we look at the chemistry of wetlands, methane in the atmosphere, perhaps even the origin of life on Earth.

The laboratory where ghosts are born

Richard Zare, chemist of the Stanford University, has been studying bubbles for years. In his lab, he built a nozzle that shoots methane and air into a transparent tank. High-speed cameras pointed at the bubbles. And there, in the middle of the water, something happens that no one had ever filmed before: submillisecond flashes of light between approaching bubbles. The team published the results on Proceedings of the National Academy of Sciences, closing a centuries-old enigma.

When bubbles are at the interface between water and air, the electrical charges on their surfaces separate: negative charges accumulate on the smaller bubbles, positive ones on the larger ones. This difference generates electric fields over small distances that trigger microlightning. "No one thinks that water can be linked to fire," Zare commented.

"It's thought that water puts it out. No one had explained to us that starting from water, you can create a spark and set something on fire: this is new."

Will-o'-the-wisps: cold oxidation, not combustion

The high-speed camera filmed the tiny flashes of light created by the colliding bubbles. Other instruments detected ultraviolet light from the fluorescence of formaldehyde, a compound produced when methane oxidizes. But there's a detail that explains why legends always speak of lights that... “they don't heat up”: it is not a real combustion. It is cold oxidationA chemical reaction that produces light without significant heat.

James Anderson, a Harvard chemist not involved in the study, called the discovery “a really exciting step forward” because it reveals a mechanism by which chemical reactions can be triggered without external ignition sources.

Centuries of legends, a laboratory explanation

For centuries, will-o'-the-wisps have fueled legends around the world. In Scotland, they were called spunkies. In Japan hitodama, souls of the dead. In Anglo-Saxon folklore they were the will-o'-the-wisp, the lanterns of Will, an evil blacksmith cursed to wander for eternity with a burning coal to lure travelers into a trap. All these stories concealed a real phenomenon: blue-green lights that appeared above swamps, peat bogs, and cemeteries, especially on warm summer evenings.

The chemical basis had long been known. Marshes are methane factories: they are oxygen-poor environments where microbes decompose organic matter, producing gas. The acidic environment slows decomposition, and methane accumulates and rises. But methane alone doesn't ignite at low temperatures. An explanation for the initial spark was needed. According to Phys.orgPrevious hypotheses included phosphine (a highly unstable gas that self-ignites) or electrostatic discharge, but none had solid experimental evidence.

Methane, climate and unexpected consequences

The discovery of microlightning doesn't just solve a folkloric puzzle. It has implications for environmental chemistry and climate. As we have reported in the pastMethane is an extremely potent greenhouse gas, responsible for approximately 30% of global warming since pre-industrial times. Wetlands are a major natural source of emissions. Understanding how methane interacts with the environment, including the mechanisms of spontaneous oxidation, helps build more accurate climate models.

But there's more. Zare and his team had already hypothesized, in previous studies published in Science Advances, that microlightning strikes between water droplets may have provided the sparks needed to create the biomolecules essential to life on early Earth. If tiny electrical discharges can trigger complex chemical reactions without the need for atmospheric lightning, then the origin of life may have been much more "local" than we thought. No need to wait for a thunderstorm: all it takes is a bubble of water in the right place.

Will-o'-the-wisps: Volta was right, but for the wrong reasons.

In the end, Alessandro Volta was right. Electricity did indeed have something to do with it. Only it wasn't a bolt from the blue, as he thought. It was something much smaller, hidden among the bubbles. As Scientific American notes, the discovery is the result of modern technologies applied to ancient questions: high-speed cameras, spectrometers, photon counters.

Will-o'-the-wisps remain rare to observe today. Perhaps because wetlands have shrunk. Perhaps because artificial lighting has rendered such faint lights invisible. Or perhaps, as some skeptics suggest, because travelers once carried open-flame lanterns that could ignite methane. But now we know that the mechanism exists, works, and can be reproduced in a laboratory.

Legends speak of spirits that move away when you approach. The explanation is simpler: your movement creates air currents that disperse the gas and extinguish the reaction. No magic, just fluid dynamics. But the fact that water can generate sparks strong enough to ignite something is, ultimately, strange enough to seem like magic.

Only this time we know how it works.