By Peter Weiss
Two years into his doctoral research, which had him looking long and hard at bubbles rising in a liquid, Alberto Tufaile noticed something odd. Sometimes, a few small bubbles would circle around in his flasks instead of rising to the top. “I was worried because I couldn’t explain what I was seeing,” recalls Tufaile, now a physicist at the University of São Paulo in Brazil. Ensnared by these oddball bubbles, Tufaile scoured the scientific literature and consulted with colleagues in search of clues. He got nowhere until one day in 1998, while searching the Web, he hit upon an amateur scientist’s site. He then realized that those slow-go bubbles were not ordinary bubbles at all. They were tiny balls of water enclosed by microscopically thin shells of air, the whole package surrounded by water.
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The eye-opening Web site, the work of engineer Chris T. Nadovich of Sellersville, Pa., described most of what was then known about structures called antibubbles, which was not much. It described them as the opposites of soap bubbles, which consist of air, enclosed by a film of liquid, immersed in air. Most antibubbles span less than a centimeter in diameter—although they have been made as big as racquetballs—and their air shells are about as wide as red blood cells.