David Pines sat down in 1956 and described a particle that had never been seen. Not because he had seen it either, but because the math said it had to exist. He gave it a name, sketched out its properties, and sent the idea into the world. For 67 years, nobody could prove him right.

What happened next involves a laboratory that wasn’t looking for it, a metal that shouldn’t have contained it, and a discovery that arrived sideways while scientists were chasing something else entirely. And buried inside all of it is a question that physicists have been trying to answer for decades: why does electricity have to lose so much energy in transit, and what would change if it didn’t? Hold that question. It matters more than it might seem right now.

The Particle That Hides in Plain Sight

David Pines predicted something strange. Electrons in certain metals, he argued, could combine in a very specific out-of-phase pattern and form an entirely new kind of particle, one with no mass and no electric charge. Because electrons in different energy bands would be moving in opposite directions at the same time, their charges would cancel each other out completely. What remained would be a ripple moving through the material, invisible to almost every instrument scientists had.

He named it a demon. Not out of drama, but because the physics demanded an acronym: distinct electron motion, with the standard “-on” suffix that physicists attach to particles. Pines’ demon. A massless, chargeless quasiparticle that left no fingerprint in any standard experiment. And that was precisely the problem.

Most experiments in condensed matter physics rely on light. You shine it at a material, measure how it bounces or bends, and read what comes back. A neutral particle that doesn’t interact with light produces nothing for those instruments to catch. Pines’ demon could have been sitting inside a hundred different metals for seventy years, and nobody would have known. Standard tools were blind to it by design.

Finding it would require a completely different approach. And for nearly seven decades, almost nobody attempted one.

A Team That Wasn’t Looking for It

Researchers at the University of Illinois Urbana-Champaign were studying a metal called strontium ruthenate. Their reason had nothing to do with demons. Strontium ruthenate behaves in ways that resemble high-temperature superconductors without actually being one, and the team wanted to understand why. What gives certain materials their strange properties without crossing into full superconductivity?

To investigate, they used a technique called momentum-resolved electron energy-loss spectroscopy. Less commonly used than optical methods, it works by firing electrons directly at a crystallized material and measuring the energy those electrons carry when they bounce back. From that data, researchers can track how plasma waves move inside the metal. It reads the material’s electronic behavior directly rather than waiting for it to show up in reflected light.

As they worked through the data from strontium ruthenate, something appeared that didn’t fit any category they expected. A quasiparticle moving through the material at a speed that made no sense. Too slow to be a surface plasmon. Too fast to be an acoustic phonon. Not anything the team had set out to find.

“At first, we had no idea what it was,” said Ali Husain, a co-author who is now a physicist at the quantum technology company Quantinuum. “Demons are not in the mainstream. The possibility came up early on, and we basically laughed it off. But, as we started ruling things out, we started to suspect that we had really found the demon.”

They ran follow-up experiments. Four different crystals of strontium ruthenate, five separate measurements. Every time, the same result came back. A massless electronic mode moving through the material exactly as Pines had predicted in 1956. When theorist Edwin Huang performed calculations on strontium ruthenate’s electronic structure, he found two electron bands oscillating out of phase with nearly equal magnitude, precisely the conditions Pines had described as necessary for a demon to exist. Sixty-seven years after the prediction, a team that had been looking for something else entirely had found it.

Why Superconductors Keep Everyone Up at Night

To understand why this matters, it helps to know what a superconductor actually does. Ordinary electrical conductors, such as copper wire, aluminum cable, and the infrastructure carrying power across cities, lose energy constantly. Electrons moving through a material bump into atoms, generate heat, and bleed off a portion of whatever they were carrying. Power grids around the world lose enormous amounts of electricity this way before it ever reaches its destination. It’s an accepted inefficiency, built into every calculation, baked into every energy budget.

Superconductors change that. Inside a superconducting material, electrons pair up and move together in a way that produces zero electrical resistance. No heat lost. No energy bled off. Electricity moves through as if the material weren’t there at all.

Achieving this in practice requires extreme cold. Most superconductors only work at temperatures near absolute zero, which means expensive cooling systems and severe practical limitations. High-temperature superconductors work at comparatively warmer conditions around negative 130 degrees Celsius, but that’s still far from anything useful at everyday temperatures.

A room-temperature superconductor, one that works without any cooling at all, would change everything. Power grids could carry electricity across continents with near-zero loss. Quantum computers could operate outside of laboratory conditions. Medical imaging technology could become cheaper and more accessible. Scientists call it the holy grail of modern physics, and they mean it.

Nobody has cracked it yet. Part of the reason is that nobody fully understands how superconductivity works in certain materials.

What the Standard Theory Gets Wrong

Standard superconductor theory, known as BCS theory, describes a specific mechanism: quantum-scale sound waves inside a material, called phonons, nudge electrons into pairs. Those paired electrons, called Cooper pairs, move together in a way that eliminates resistance. It’s an elegant explanation, and it holds up well for conventional superconductors.

High-temperature superconductors are a different story. BCS theory struggles to explain them. Something else is pairing the electrons, something the theory doesn’t account for. Physicists have debated what that something might be for decades. Pines’ demon is one serious candidate.

Because the demon is massless, it can form at any energy level. And because it can form at any energy level, it can potentially exist at any temperature, including room temperature. If demons are actively pairing electrons inside high-temperature superconductors, finding out how they do it could give scientists a blueprint for building better ones. Materials that achieve superconductivity without needing to be cooled to temperatures that only exist at the edge of the observable universe.

Peter Abbamonte, the physics professor who led the Illinois team, put the broader lesson plainly: “It speaks to the importance of just measuring stuff. Most big discoveries are not planned. You go look somewhere new and see what’s there.”

That philosophy drove the discovery. A technique that isn’t widely used, applied to a material that hadn’t been studied in this way before, produced a result nobody had planned for. Science at its most honest.

What Strontium Ruthenate Actually Revealed

When researchers fired electrons at the crystallized metal and tracked what came back, they found an acoustic mode, a wave moving through the material that matched Pines’ predictions in almost every measurable way. Its velocity fell between the velocities of two distinct electron bands inside the metal, exactly as the theory required. Its intensity scaled in a way that confirmed it carried no electric charge. Its behavior at different temperatures and across different crystal directions remained consistent with a true demon rather than any other known particle type.

What made the detection possible was precision. Previous instruments lacked the momentum resolution to isolate the demon’s signature. It moves at a speed and scale that older equipment would have averaged out and missed entirely. Abbamonte’s team used a modified spectrometer with high enough resolution to catch what earlier measurements had swept past without noticing.

Theoretical calculations confirmed what the experimental data showed. Strontium ruthenate’s electronic structure, when worked out properly, produced exactly the out-of-phase oscillation between two electron bands that Pines had described as the demon’s defining characteristic. It wasn’t a coincidence or an artifact. It was the thing itself.

A Discovery That Opens More Doors Than It Closes

Confirming a 67-year-old prediction is significant on its own. But what the discovery points toward matters more than the confirmation itself. Strontium ruthenate is almost certainly not the only metal that contains a demon. Pines argued that any material with electrons in more than one energy band could potentially harbor one. Strontium ruthenate simply happened to be where the right technique met the right material at the right moment. Researchers now suspect demons may be far more common across multiband metals than anyone previously assumed, hiding in materials that have never been examined with sufficient precision.

A more complete theory of how demons behave still needs to be built. Current mathematical frameworks describe their basic properties but don’t fully account for everything the Illinois team observed. Physicists are calling for more sophisticated experiments, potentially using high-energy electron microscopes to study demon behavior in finer detail across a wider range of materials.

If demons do turn out to mediate superconductivity in high-temperature materials, the path forward becomes clearer. Identify which materials contain them. Understand exactly how they pair electrons. Design new materials where that pairing can happen without extreme cooling. None of that happens quickly, and none of it is guaranteed. But the starting point, the existence of the demon itself, is no longer theoretical.

A Lifetime Between Prediction and Proof

David Pines made his prediction in 1956. He died in 2019. He didn’t live to see his demon confirmed. Science operates on timescales that don’t accommodate urgency. An idea can sit unverified for decades, not because it’s wrong but because the tools to test it don’t exist yet, or because the right person hasn’t pointed the right instrument at the right material on the right day. Pines waited a lifetime. His demon waited longer.

What a team in Illinois found while looking for something else entirely may turn out to be one of the more consequential accidental discoveries in recent physics. A massless particle that doesn’t interact with light, predicted in the Eisenhower era, was pulled out of a metal by researchers who laughed off the possibility before the data made them stop laughing.

Near-lossless electricity. Power that travels without bleeding off into heat. A grid that delivers what it generates instead of surrendering a portion of it to the physics of imperfection. None of that exists yet. But the particle that might help make it possible just showed up in a laboratory in Illinois. It was hiding in the measurements the whole time. Someone just had to look.

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