Great balls of fire
According to National Geographic News, two Brazilian physicists of the Federal University of Pernambuco have created artificial ball lightning in their lab. Like the ones you may have seen during a thunderstorm, these ball lightning move erratically and burn whatever they touch, even drilling a hole in one of the researcher's jeans. The scientists may have solve a mystery which was several centuries old by confirming the theory that balls of lightning are a result of silicon combustion. Anyway, the team was able to keep these nasty balls alive for about 8 seconds. Read more...
First, what is the theory that the Brazilian physicists confirmed?
John Abrahamson and James Dinniss, of the University of Canterbury in Christchurch, New Zealand, first proposed the ball-lightning theory that lies behind Pavão's research. The pair suggested that when lightning strikes a surface, like the Earth's silica-rich soil, a vapor is formed. This silicon vapor may condense into particles that combine with oxygen in the air to slowly burn with the chemical energy of oxidation.
The team of physicists, Antonio Pavão and Gerson Paiva, took two years to build an experiment which could confirm this theory.
They used electrodes to shock silicon wafers with enough electricity to create a silicon vapor. Most of the artificial orbs lasted two to five seconds, but at least one has survived as long as eight seconds—approximating natural ball lightning and far exceeding previous efforts to create the phenomenon in the lab.
A video is available from this page. Below you can see the Brazilian physicists applying an electrode to silicon wafers to create electrified silicon vapor (Credit: Antonio Pavão).
And below is the result. "The luminous orbs the size of ping-pong balls persisted for up to 8 seconds, with smoke trails that formed spiral shapes, suggesting the balls were spinning" (Credit: Gerson Paiva).
In a slightly older article, "Lightning balls created in the lab," New Scientist gave more details about how the team tested his ideas (Hazel Muir, New Scientist, January 10, 2007). The bottom photo on this post has been extracted from this article.
[They] 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.
So ball lightning is losing its status as a mystery. Fine! But besides that, don't expect many practical applications to emerge from this experiment.
Sources: Brian Handwerk, for National Geographic News, January 22, 2007; and various other websites
You'll find related stories by following the links below.