Physicists in Austria say they have solved the conundrum of "ball lightning", mysterious glowing spherical apparitions which baffled boffins have struggled to explain for centuries.

According to Josef Peer and Alexander Kendl of the University of Innsbruck, there is in fact no such thing as ball lightning in reality. Rather, powerful magnetic fields created by ordinary lightning affect the brains of humans nearby so that they see things which aren't there.

According to Peer and Kendl's calculations, a certain type of long-lasting repetitive lightning strike emits magnetic fields very similar to those used in transcranial magnetic stimulation (TMS) - a medical technique use to hotwire activity in the brain.

“In the clinical application of TMS, luminous and apparently real visual perceptions in varying shapes and colors within the visual field of the patients and test persons are reported and well examined,” says Kendl.

Thus the right kind of lightning strike nearby affects people's brains, accounting for long-accumulated reports of mysterious "ball lightning" phenomena during thunderstorms. Scientists have always struggled to explain just how these strange glowing spheres would be generated and sustained: it now appears at least possible that they aren't, in any physical sense.

Apparently an artificially induced image in the brain is called a "phosphene". Kendl adds:

“An observer located within few hundred metres of a long lightning stroke may experience a magnetic phosphene in the shape of a luminous spot."

The physicist says that this is much the simplest and likeliest explanation for ball lightning.

“Contrary to other theories describing floating fire balls, no new and other suppositions are necessary," he says, uncompromisingly.

The two boffins' paper is to be published in the journal Physics Letters A. It can also be read here. ®