What is ball lightning?

In October 1638, during a violent storm, something described as a great ball of fire came through the door of a church in Widecombe-in-the-Moor, England, killed four people, and left scorch marks argued about ever since. Reports like it have accumulated for centuries: a luminous sphere, usually the size of a grapefruit, appearing near a lightning strike, drifting horizontally for several seconds, passing near or reportedly through windows, then vanishing quietly or with a bang. The reports are too numerous and too consistent to dismiss. There is still no accepted explanation.

Why it matters

Ball lightning matters partly as atmospheric physics and partly as a test case for how science handles rare, unrepeatable events. A self-contained ball of plasma that persists for seconds without a power source should not be possible; ordinary plasma at that temperature disperses in milliseconds. Whatever sustains it, if it is real, involves physics of confinement or slow energy release that we have not pinned down, with occasional practical echoes in fusion research, where holding plasma together is the entire problem.

What has been tried

Theories have multiplied for two centuries: plasma vortices, microwave radiation trapped in a plasma shell, electrochemical glows, and even the hypothesis that some sightings are hallucinations induced by the magnetic pulse of a nearby strike. The leading natural mechanism, proposed by Abrahamson and Dinniss in 2000, holds that lightning striking soil vaporizes silicon, which condenses into nanoparticle chains that burn slowly in air as a glowing ball. In 2012 that idea received its one piece of direct field evidence: Chinese researchers surveying a thunderstorm accidentally recorded a ball lightning event with spectrographs and found emission lines of silicon, iron, and calcium, the elements of soil. Laboratory experiments have produced glowing plasmoids from underwater discharges and silicon arcs, but they are dimmer and briefer than what witnesses describe.

Where the edge is

One spectrum is evidence, not a verdict. No laboratory has produced the full phenomenon on demand, no theory accounts for all credible reports, and the reported ability to pass through glass fits almost none of them. It remains possible that ball lightning is several different phenomena filed under one name.

What would count as an answer

Reproduction on demand: a laboratory ball with the observed size, brightness, lifetime, and motion, made by a mechanism shown to operate in real storms. Short of that, several more instrumented field recordings agreeing on the physics would move this entry to the solved room.