With apologies to William Blake, who once urged us to “see a world in a grain of sand,” the speck that Paul Steinhardt is holding — glued to the point of a glass needle because you’d never find it again if it weren’t — is barely visible to the naked eye. Steinhardt’s enthusiasm notwithstanding, a visitor to his fourth-floor office in Jadwin Hall is only being polite when he acknowledges that he can see it at all.
But Steinhardt is a theoretical physicist, so let your mind bore in to the atomic level. This speck is called a quasicrystal, a rare 20-sided clump of atoms that violates what were long believed to be the most basic rules of crystalline structure. Three decades ago, an Israeli physicist, Daniel Shechtman, stumbled upon man-made quasicrystals in a piece of industrial aluminum and later received the Nobel Prize for his discovery. But Steinhardt already had deduced that such structures might exist, and it was he and his co-author who explained what Shechtman had found.
Having looked within, now pull back. Rewind the probable history of this speck like one of those reverse-action films in which the diver emerges feetfirst from a pool and arcs up onto the board. Follow it back to the piece of khatyrkite, the rare mineral in which it once was embedded; back into the white cardboard box in the collection of the University of Florence; back into the black-market collection of an Amsterdam gem dealer. Go further, to the remote Russian stream bed where a platinum prospector first picked up the khatyrkite 32 years ago, to the glacier that dropped it during the last Ice Age 15,000 years ago, to the meteorite that disintegrated in the atmosphere and rained stardust over Siberia.
Don’t stop. Reassemble that meteorite and pull it back into the sky, out of our galaxy, out into the farthest reaches of space, where Steinhardt thinks it may have formed in a collision with another meteorite. Chemical analysis suggests that this little bit of metal ricocheted around the universe for 4.5 billion years. It is older than our solar system yet something never seen before, and it could fit on the head of a pin.
How about that, William Blake?
Officially, Steinhardt is the Albert Einstein Professor in Science (and director of the Princeton Center for Theoretical Science), but his three-decade investigation of quasicrystals has required him to be part Carl Sagan, part Indiana Jones, part Lewis and Clark, and part Sherlock Holmes. Throw in a touch of Captain Ahab, as well, for it is not too much to say that in the world of crystallography those rare specks of metal have become — if one can lurch to the opposite end of the metaphorical scale — the Great White Whale.
Face to face, Steinhardt is mild-mannered and engaging, with an uncommon ability to explain opaque scientific concepts in layman’s terms. That is helpful, for his interests range among particle physics, dark energy, astrophysics, and cosmology. One of the founders of an inflationary model of the universe, which holds that the early universe underwent a period of exponentially rapid expansion, he since has developed a competing theory, a so-called cyclic model, which posits that the universe oscillates through periods of expansion and contraction. (See “The Cosmic Apocalypse,” PAW, Feb. 11, 2009.) A prolific writer and lecturer, Steinhardt has co-authored one book and edited four more, published more than 200 journal articles, and received six patents relating to quasicrystals, with two more pending.
The best way to understand quasicrystals is to look at something two-dimensional. Think of your bathroom floor. Chances are, the tiles are laid in a regular, repeating pattern. If the pattern is made with a single type of tile, only certain shapes — three-, four-, or six-sided — can be used to fill the space completely. Use pentagons, octagons, or any other shape, it was believed, and there will be space left over.
Physicists long thought that the atoms inside a crystal also arranged themselves in repeating patterns. Like those floor tiles, only certain shapes were permissible, and only certain types of symmetries — two-, three-, four-, or sixfold — were possible (in other words, each piece or atom could be rotated a certain number of degrees and still fit in the pattern). Starting in the 1960s, mathematicians tried to see if it were possible to arrange tiles in a pattern that never repeated itself — that was, to use the scientific term, nonperiodic. A British mathematician, Roger Penrose, created such a pattern using two shapes, a fat and a thin rhombus.
In the early 1980s, Steinhardt began working with a graduate student, Dov Levine (now a theoretical physicist in Israel), when both were at the University of Pennsylvania, to see if they could find atomic arrangements with supposedly impossible symmetries. Looking at Penrose’s two-dimensional mosaic, they discovered that the pattern thought to be nonperiodic was actually quasiperiodic, meaning that the pieces did follow a pattern, although that pattern never perfectly repeated itself.
At the same time, Shechtman, working at what is now the National Institute of Standards and Technology, accidentally discovered an aluminum alloy that, when viewed under an electron microscope, was seen to contain crystals with fivefold symmetry. Not only did no one believe him — crystals couldn’t have fivefold symmetry — his supervisor reassigned him and suggested that he learn something about crystallography. It took two years before any scientific journal would agree to publish Shechtman’s findings.