From discovering improbable new materials to challenging conventional wisdom in early-universe cosmology, Steinhardt is at his best when grappling with big unanswered questions.
There’s something about the word “impossible” that gets Paul Steinhardt motivated.
He has defied the impossible before and hopes to do it again.
“That moment of realization, when you uncover something fundamentally new, is my dopamine fix,” he says. “Especially if it’s something supposedly impossible.”
His dopamine was flowing when he and his Italian collaborator, Luca Bindi, tracked down a rock that his colleagues had assured him simply could not exist.
The rock, which turned out to be a meteor older than the Earth itself, exhibited a quasicrystal structure that Steinhardt had proposed theoretically decades earlier — a structure widely believed to be possible only in blackboard theorems, not in nature.
Steinhardt never dreamed he’d be chasing rare rocks. He’s a cosmologist, not a geologist, whose research has sought an answer to what is considered by many an unanswerable question: what happened before the Big Bang?
Natural quasicrystals and other improbable materials
He was preoccupied mostly on such cosmological challenges when, in the early 1980s, Steinhardt and Dov Levine hypothesized the existence of quasicrystals, describing their unique quasiperiodic structure. Soon after, laboratory-synthesized quasicrystals were discovered, and Steinhardt wondered if these exotic structures could exist naturally; experts in minerals and crystals assured him they could not.
When Steinhardt and Bindi discovered grains in a rock sample with the characteristic signature of a quasicrystal in 2009, it started an international detective story that included mineral smugglers and searches for missing persons. Ultimately, Steinhardt organized a geologic expedition to the Russian Far East to verify the find and collect samples.
Careful analysis of the samples revealed not just one, but three different types of natural quasicrystal that formed inside a meteor 4.5 billion years ago — confirming that, long before humans, nature found a way to create “impossible” substances.
“There was a lot of skepticism that quasicrystals could exist naturally,” recalls Steinhardt, who earned his PhD at Harvard in 1978 and held a professorship at the University of Pennsylvania until joining Princeton in 1998. “But finding them in a meteorite — a material formed billions of years ago in the early solar system — completely changed that perception.”
Steinhardt’s hunt for improbable materials continues. A newly discovered mineral was named “steinhardtite” in his honour by the International Mineralogical Association, and now he’s seeking even stranger stuff.
“A group of us have recently been studying a new class of structures we call aperiodic hyperuniform tessellations,” he explains. “These materials are neither quasicrystals, glasses, nor traditional crystals. They’re something entirely new, and they could serve as templates for advanced photonic materials.”
Such photonic materials, he said, could have profound impacts in computing and communications, replacing fibre-optic cables with more efficient and durable nano-scale structures. He has already patented nearly two dozen technologies including quasicrystals and photonic circuits (alternatives to traditional electronic ones).
Refining the cyclic cosmology model
Meanwhile, Steinhardt continues his unconventional research in cyclic models of early-universe cosmology, which reimagines the cosmos as an eternal cycle of expansion and contraction, rather than a singular Big Bang.
Steinhardt co-authored the 2007 book Endless Universe with Neil Turok, and both researchers have evolved their theories about cosmic evolution since its publication.
“The work I’m doing now on bouncing cosmology is very different from the ideas I pursued with Neil Turok years ago,” he explained in a recent interview. “We’ve refined the models, eliminated unnecessary assumptions like extra dimensions, and gained a better understanding of how the universe could become smooth and flat during contraction.”
Steinhardt’s current cyclic model addresses what he says is a flaw in traditional inflationary theory: the lack of a detailed explanation for how the universe becomes smooth and flat after the Big Bang. The numerical relativity simulations he and his colleagues developed demonstrate how a “slow contraction” (rather than inflation) can smooth and flatten the universe before it expands in its next bounce.
“During contraction, the equations simplify into ordinary differential equations,” he explains. “Every point in space independently follows the same equation of motion, which naturally leads to a homogeneous and isotropic universe. It’s an incredibly powerful smoothing and flattening process.”
Whereas inflationary theory relies on rapid expansion to essentially iron-out irregularities in the cosmos, Steinhardt’s cyclic model achieves the same result through contraction, avoiding the chaotic quantum fluctuations that plague inflationary models.
“The lesson from inflation is to avoid any phase where quantum gravity dominates,” he says. “Bouncing models allow you to do that while maintaining the classical physics that governs the universe.”
Steinhardt’s ideas tend to challenge conventional wisdom — a big bounce instead of a bang, rocks that shouldn’t exist — and span an array of fields. There, in the world of big unanswered questions, is where he gets the best dopamine.
“I’ve never found myself grinding,” he says. “If I hit a dead end in one area, I set it aside and work on something else, and then suddenly something comes to light again.”
