Audio Edition: Heat Destroys All Order. Except for in This One Special Case.
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Welcome to the Quanta Audio Edition. In each of these bi-weekly episodes, we bring you a story direct from the Quanta website about developments in basic science and mathematics. I'm Susan Vallett. Heat is supposed to ruin anything it touches. But physicists have now shown that there is a substance that is truly heat-proof, and it's an idealized form of magnetism. That's next. ♪

Quantum Magazine is an editorially independent online publication supported by the Simons Foundation to enhance public understanding of science. Sunlight melts snowflakes. Fire turns logs into soot and smoke. A hot oven will make a magnet lose its pull. Physicists know from countless examples that if you crank the temperature high enough, structures and patterns break down.

Now, though, they've cooked up a striking exception. In a string of results over the past few years, researchers have shown that an idealized substance resembling two intermingled magnets can, in theory, maintain an orderly pattern no matter how hot it gets. The discovery might influence cosmology or affect the quest to bring quantum phenomena to room temperature.

Fabian Renecke is a researcher at the Institute for Theoretical Physics in Gießen, Germany, who wasn't involved in the work. He says the idea that such an effect is possible, even if only in theory, hits you in the face because it's not what you expect. Jörg Schmalian, a physicist at the Karlsruhe Institute of Technology in Germany, is intrigued too. He says he's thinking about how to find a concrete realization of this framework.

The discovery was sparked by an audience question at a lecture at the Hebrew University of Jerusalem in 2019. Zohar Komargotsky, a physicist visiting from Stony Brook University, had commented that any form of order, such as the regular spacing of atoms in a solid or the alignment of atoms in a magnet, inevitably breaks down at sufficiently high temperatures,

An audience member, Eliezer Rabinovitchi of Hebrew University, asked Komargotsky if he was certain this was true. After the talk, the two began to collaborate along with other colleagues.

They weren't the first physicists to wonder. In the 1950s, Isaac Pomeranchuk had calculated that slightly heating supercooled liquid helium-3 atoms would make them freeze. A crystal known as Rochelle salt, which is used as a laxative, shifts to a more ordered structure at warmer temperatures.

Curiosities like these motivated the physicist and future Nobel laureate Steven Weinberg to develop an idealized quantum theory of heat-resistant order in the 1970s. But in both liquid helium and Rochelle salt, further heating destroys that order. And Weinberg's theory also failed above a certain temperature. Was it possible for some pattern to persist forever, no matter how hot it got?

Komargotsky, Rabinovich and collaborators tried to find out. The physicists homed in on something many of us experience in our lives every day: magnetism. Picture a bunch of atoms arranged in a square grid. Each atom acts like a mini-magnet, with a north pole that points up or down. If the atoms line up in some pattern, all pointing the same way, for instance, the material has magnetic order.

Imagine laying this grid directly on top of a second atomic grid. These new atoms can swing freely, pointing in any direction, as opposed to only up or down. Nearby atoms will interact, with ripples in one grid triggering ripples in the other. Now, zoom out until the grid lines disappear and the system becomes a smooth sheet, a quantum field.

The atoms have vanished, but the field still has two magnetic arrows at every point, one pointing straight up or down, and another pointing in any direction. It's this kind of idealized field that researchers realized could maintain magnetic order at every temperature. Under cool conditions, the up-down arrows nudge each other into alignment, all up, let's say, while the freewheeling arrows point in random directions.

As the temperature rises, one would expect the thermal energy to start flipping all the arrows violently, washing out any alignment. But it doesn't. The free arrows pinwheel around more, stabilizing the magnetic order in the up-down arrows. And this arrangement survives even as the temperature climbs higher for all eternity. The magnetic order never melts away.

A caveat is that the trick seems to work best when the freewheeling arrows have a great deal of freedom. Komar Gotsky imagines arrows that are free to point in any direction in an abstract space of hundreds of dimensions. But these don't have to be literally directions in real space. They represent all the ways the field can vary mathematically from point to point.

In 2020, Komargotsky and collaborators calculated that magnetism will endure in this system up to infinite temperatures. But there was one problem: their math relied on the assumption that probabilities don't have to add up to exactly 100%. That's a physical and logical impossibility.

They gave up the search for a more solid proof until this past fall, when a team of European physicists, Michael Scherer, Jun-Chin Rong, and Bilal Hawassian, advanced the case. They restored 100% probabilities, at the price of ignoring certain mild magnetic interactions, and found that order persisted for arrows spinning through as few as 15 abstract dimensions.

Their work inspired Komargotsky and a new collaborator, Fetter Popov, to return to the problem and finally find a rigorous proof of the unmeltable order that overcomes all previous shortcomings. They posted a preprint of a paper describing the work in December 2024. Scherer thinks the new proof will hold up, but he says the question is, what do we do with it now?

Knowing that order can theoretically survive any amount of heat might influence theories of the universe's birth. The typical story is that order developed as the inferno of the young universe cooled, but the recent work highlights stranger possibilities. Francesco Sanino, a physicist at the University of Southern Denmark, says this adds new theories to the toolbox that scientists can use.

Sunino has independently found proof of heat-resistant order in fundamental quantum theories. The new way of heat-proofing quantum patterns may also inspire physicists who study delicate phenomena like superconductivity, a phase in which electric current flows with no resistance.

Normally, heat disrupts the quantum ordering that makes superconductivity possible, limiting its applications. But maybe in a material that borrows key features from the magnetic theory, perfect currents could be made to endure rising temperatures.

Michael Kenyon Logo helped with this episode. I'm Susan Vallett. For more on this story, read Charlie Wood's full article, Heat Destroys All Order Except for in This One Special Case, on our website, quantummagazine.org.

And check out this feed every Tuesday for the Quanta podcast, where Editor-in-Chief Samir Patel talks to our writers and editors about more of Quanta's most popular, interesting, and thought-provoking stories. From PR.