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. To test this idea, a team led by Antônio Pavão and Gerson Paiva from the Federal University of Pernambuco in Brazil took wafers of silicon just 350 micrometres thick, placed them between two electrodes and zapped them with currents of up to 140 amps. Then over a couple of seconds, they moved the electrodes slightly apart, creating an electrical arc that vaporised the silicon. The arc spat out glowing fragments of silicon but also, sometimes, luminous orbs the size of ping-pong balls that persisted for up to 8 seconds. "The luminous balls seem to be alive," says Pavão. He says their fuzzy surfaces emitted little jets that seemed to jerk them forward or sideways, as well as smoke trails that formed spiral shapes, suggesting the balls were spinning. From their blue-white or orange-white colour, Pavão's team estimates that they have a temperature of roughly 2000 kelvin. The balls were able to melt plastic, and one even burned a hole in Paiva's jeans. These are by far the longest-lived glowing balls ever made in the lab. Earlier experiments using microwaves created luminous balls, but they disappeared milliseconds after the microwaves were switched off (New Scientist, 11 February 2006, p 16).