In 1908, the physics world woke up to a puzzle whose layers have continued to stump the greatest scientists of the century ever since. That year, Dutch physicist Kamerlingh Onnes cooled mercury down to -450° Fahrenheit and discovered—to his astonishment—that it could conduct electricity perfectly. And then for the next 50 years, no one could explain why.
Ordinary wires, even really good ones like copper, lose up to a third of the electricity they carry over long distances. But these materials, called superconductors, don’t lose any energy. Ever. You could start a current in a loop of superconducting wire and it would circle around, theoretically, forever.
This phenomenon confounded the greatest minds in physics. From papers, lectures, and the reports of former students, we know that Einstein spent a lot of time thinking about it. Everyone did; it was one of the great unanswered questions, even as scientists unraveled other mysteries like the structure of atoms and the age of the universe.
But Einstein never came up with an answer. Neither did the great quantum physicist Richard Feynman, or any of the other luminaries: Niels Bohr, Lev Landau, Werner Heisenberg, Maria Goeppert Mayer. Physicist Felix Bloch crankily suggested a new theory: “Superconductivity is impossible.”
In their labs, scientists continued to discover more and more superconductors, but the new materials didn’t seem to follow a pattern. Some were pure elements; some were alloys. Even more oddly, it turned out that normally good conductors, like copper, were worthless as superconductors. And why did they all have to be cooled down to near absolute zero to work?
“All of the great minds had a go at figuring out the theory behind superconductors,” said Argonne Distinguished Fellow and materials scientist Mike Norman. “But no one had anything good until 1957.”
That year, a trio of University of Illinois physicists published an explanation called BCS theory (for Bardeen, Cooper, and Schrieffer) that explained the odd behaviors. Satisfied, scientists shelved it away under “solved mysteries.”
That’s why no one was prepared when, in 1986, a team from a Swiss laboratory announced it had found a superconductor that worked at much warmer temperatures —up to -280°F. Although to most of us that number sounds positively frigid, for scientists studying superconductors it was a thunderclap.
BCS theory did not explain this phenomenon. Physicists were stunned. They went back to the drawing board, and that’s where they still are today, a quarter-century later. In the meantime, we’ve explained why the universe is expanding, documented what we’re made up of down to the tiniest subatomic particles, and landed a robot on Mars; but we can’t explain why these new superconductors work. More here The science that stumped Einstein.