Scientists create lightning balls in lab

Thousands of people have reported seeing ball lightning, a luminous sphere that sometimes appears during thunderstorms. It is typically the size of a grapefruit and lasts for a few seconds or minutes, sometimes hovering, even bouncing along the ground.

One eyewitness saw a glowing ball burn through the screen door of a house in Oregon, navigate down to the basement and wreck an old mangle, while in another report, a similar orb bounced on a Russian teacher's head more than 20 times before vanishing.

One theory suggests that ball lightning is a highly ionised blob of plasma held together by its own magnetic fields, while an exotic explanation claims the cause is mini black holes created in the big bang.

A more down-to-earth theory, proposed by John Abrahamson and James Dinniss at the University of Canterbury in Christchurch, New Zealand, is that ball lightning forms when lightning strikes soil, turning any silica in the soil into pure silicon vapour. As the vapour cools, the silicon condenses into a floating aerosol bound into a ball by charges that gather on its surface, and it glows with the heat of silicon recombining with oxygen.