String Theory Helps To Explain Quantum Phases Of Matter (preview)

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Newly discovered states of matter embody what Einstein called ?spooky action at a distance.? They defy explanation, but lately answers have come from a seemingly unrelated corner of physics: string theory

By Subir Sachdev

MAGNET is being levitated by an unseen superconductor in which countless trillions of electrons form a vast interconnected quantum state. Astoundingly, the quantum state of many modern materials is subtly related to the mathematics of black holes.

Image: Zachary Zavislak

In Brief

• Matter can assume many forms other than solid, liquid and gas. The electrons that perfuse materials can undergo their own transitions, which involve inherently quantum properties of matter. Superconductors are the best-known example.
• These states of matter arise from an unimaginably complex web of quantum entanglement among the electrons?so complex that theorists studying these materials have been at a loss to describe them.
• Some answers have come from an entirely separate line of study, string theory, typically the domain of cosmologists and high-energy particle theorists. On the face of it, string theory has nothing to say about the behavior of materials?no more than an atomic physicist can explain human society. And yet connections exist.

Several years ago I found myself where I would never have expected: at a conference of string theorists. My own field is condensed matter: the study of materials such as metals and superconductors, which we cool in the laboratory to temperatures near absolute zero. That is about as far as you can possibly get from string theory without leaving physics altogether. String theorists seek to describe the universe at energies far in excess of anything experienced in a lab or indeed anywhere else in the known universe. They explore the exotic physics governing black holes and putative extra spacetime dimensions. For them, gravity is the dominant force in nature. For me, it is an irrelevance.

This difference in subject matter is mirrored by a cultural gap. String theorists have a formidable reputation, and I went to the meeting in awe of their mathematical prowess. I had spent several months reading their papers and books, and I often got bogged down. I was certain I would be dismissed as an ignorant newcomer. For their part, string theorists had difficulty with some of the simplest concepts of my subject. I found myself drawing explanatory pictures that I had only ever used before with beginning graduate students.

This article was originally published with the title Strange and Stringy.

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