Ball lightning can drift through a closed window, and physicists still can’t fully explain it

For centuries, people caught in violent thunderstorms have reported seeing something that ordinary lightning cannot account for: a glowing sphere, often about the size of a grapefruit, that floats through the air for several seconds before vanishing. Witnesses describe these luminous balls drifting across fields, rolling down aircraft aisles and, most unnervingly, passing through closed windows and solid walls into rooms. The phenomenon, known as ball lightning, has been documented so widely and for so long that few scientists doubt it is real, yet no single theory has managed to explain it to everyone’s satisfaction.

What witnesses consistently describe

Across thousands of accounts gathered over generations, certain features recur. The typical ball lightning is roughly spherical, glows in shades of red, orange, yellow, blue or white, and ranges from the size of a golf ball to something closer to a beach ball. It tends to appear during or just after a thunderstorm, lasts a few seconds up to perhaps twenty, and moves in ways that seem to ignore the wind, sometimes hovering, sometimes darting. Reports often end with the ball either fading quietly or disappearing with a small explosion or pop. The consistency of these descriptions across cultures and eras is one of the strongest reasons researchers treat the phenomenon as a genuine physical event rather than a series of illusions.

The puzzle of passing through glass

The single most baffling detail is the claim that ball lightning can move through a windowpane without shattering it. Some witnesses report the sphere appearing indoors moments after lightning struck outside, as if it had slipped through the glass. Investigators who have compiled these cases note that when the ball reportedly passes through a closed window, it sometimes leaves a small hole or scorch mark, but often the glass is left apparently intact. A detailed survey of the evidence in a scientific review of the phenomenon catalogs many such indoor sightings, and the difficulty of reconciling them with known physics is a large part of why the topic remains open, as the peer-reviewed review of ball lightning discusses at length.

The plasma-bubble idea

One family of explanations treats ball lightning as a ball of plasma, a hot, ionized gas. The trouble is that plasma at high temperature should rise and dissipate almost instantly, not linger near the ground for many seconds. To keep a plasma stable for so long requires some mechanism to confine it. Physicists have proposed that microwave radiation, generated at the tip of a lightning stroke, could be trapped inside a bubble of ionized air, with the radiation pressure holding the plasma shell together. This relativistic-microwave model, laid out in a published theoretical paper, even offers a way to explain the window mystery, since microwaves can in principle pass through glass and re-form a glowing ball on the far side.

The burning-silicon hypothesis

A very different explanation abandons plasma altogether. In this view, when lightning strikes soil rich in silica, the intense heat vaporizes the ground and reduces silicon compounds to tiny particles of pure silicon. Lofted into the air, these particles slowly oxidize, glowing as they burn and releasing their stored chemical energy over several seconds. That would account for the object’s persistence, its low temperature relative to a true plasma, and its eventual fizzling out. Laboratory experiments have produced small glowing balls by vaporizing silicon and related materials, lending the idea some empirical support, though the artificial versions have not fully matched the size and behavior of the storm-born originals.

The view through the glass, without the glass moving

Another set of proposals sidesteps the need for anything to physically penetrate a window. In these models, an electric field building up outside a pane can induce a discharge on the inside surface, so that a ball appears to form indoors without any object actually crossing the glass. The apparition would be a fresh discharge excited by the field, not the same ball squeezing through solid material. Such ideas are appealing because they respect the barrier of intact glass, but they struggle to explain the full range of indoor sightings, and they remain one competing account among several rather than a settled answer.

Why the mystery endures

The central obstacle to solving ball lightning is that it cannot be summoned on demand. It appears unpredictably during storms, lasts only seconds, and has almost never been captured by scientific instruments under controlled conditions. A single well-documented spectrum, recorded by chance by researchers who happened to have equipment pointed at the right patch of sky, suggested the presence of silicon, iron and other elements consistent with vaporized soil, a finding that gave the burning-particle idea a boost. But one measurement cannot resolve a centuries-old debate. As overviews aimed at the public, including a feature on the phenomenon, make clear, ball lightning sits at an unusual crossroads: abundant eyewitness testimony, several plausible mechanisms, and not enough hard data to crown a winner. Until someone reliably reproduces or records it, the glowing sphere that seems to drift through walls will remain one of the atmosphere’s most stubborn open questions.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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