The Theorist, the Tundra, & the Forbidden Crystal
Paul Steinhardt looks like a tidy and successful lawyer, though a touch geeky. He’s a physicist whose fields include the gritty physics of matter, the first instants of the universe, and the possibility that the universe won’t end, it’ll just cycle. He’s a theorist, that is, he uses computers, math, and his brains to make sense of data that the more hands-on experimentalists collect. So how odd to hear that he’s just back from an expedition to the Koryak mountains in far east Russia, farther east than Siberia, on what he thought was a 1 percent chance that he’d find a rock from outer space containing a forbidden crystal. “My wife was quite calm until we left Anadyr,” he said, and then she texted him, “this is absolutely crazy why are you doing this,” but the tundra doesn’t have wireless so he couldn’t answer. “My sanity was questioned,” he said. But he found the rock, and in it was the forbidden crystal.
“Forbidden” really is the word physicists use. The physics of crystals is old, settled science: crystals are made of certain standard building blocks with certain standard shapes that can be regularly repeated – so squares, triangles, rectangles, parallelograms, and hexagons, that is, 2-, 3-, 4-, and 6-fold symmetry. All other symmetries are forbidden and in particular, no 5-fold symmetry; pentagons won’t repeat regularly, they have funny spaces between them. But in 1981, Steinhardt and a colleague theorized a way to regularize 5-fold symmetry, and called their putative invention, a quasicrystal. About the same time, an experimentalist arguably synthesized quasicrystals; and since then many more labs, using vacuum chambers and delicately controlling the composition and cooling time, made many more quasicrystals.
So maybe they’re not forbidden in the lab but surely they are in nature. Quasicrystals are too complicated, physicists said; the conditions of their creation are too delicate, they’re metastable and wouldn’t last. But Steinhardt and his collaborators thought maybe in certain circumstances, they might be both natural and robust. So in 1999, Steinhardt and a Princeton undergraduate wrote a little software to search a database of over 8,000 minerals for the rough signatures of any quasicrystals; then located, collected, and had the likely ones more precisely tested. “It’s hard to describe how tedious this was,” he said, “several months per sample for several years, and they all turned out to be duds. We wrote a paper that said ‘Duds. But we’re not done yet.’” That was 2001.
In 2007, Steinhardt got an email from Luca Bindi, a minerologist at the Museum of Natural History in Florence, Italy, who, as it eventually turned out, had in his collection a tiny rock with a tinier crystal of copper, iron, and aluminumthat he sent to Princeton for testing, and “right off the bat,” said Steinhardt, “it was an absolutely gorgeous quasicrystal pattern.” Obvious next question: ”So how did nature manage to do this?”
Steinhardt went up the street to ask a famous Princeton geologist who said he could believe the quasicrystal part, but the metallic aluminum in the crystal was impossible – aluminum always comes accompanied with oxygen, and the only way it could come alone naturally would be if it had formed deep inside the earth or in space. So Steinhardt and the geologist took the train down to the Smithsonian to ask the expert in meteorites who said he didn’t need to see it, a meteorite with metallic aluminum was impossible. But by now, Steinhardt had figured out that by “impossible,” geoscientists just meant “very, very unlikely,” so he and Bindi decided to find where the quasicrystal came from and how it got to Bindi’s museum.