A physicist once cooled a substance to –452°F—what happened?

The Coldest Lab in the World

Heike Kamerlingh Onnes ran the cryogenic laboratory at Leiden University in the Netherlands, where he spent years pushing the boundaries of low-temperature physics. On April 8, 1911, he achieved what no scientist had managed before: he cooled a sample of mercury wire to 4.2 Kelvin, or –452 degrees Fahrenheit, just a few degrees above absolute zero. At that temperature, something extraordinary happened. The electrical resistance of the mercury—the property that makes wires heat up when current flows through them—vanished completely.

A current started in a superconducting loop would, in theory, flow forever without losing energy. Onnes called the phenomenon superconductivity, and it defied every known law of classical physics. He had discovered a new state of matter, one where electrons move through a material as if it were a perfect highway with no friction, no obstacles, and no energy loss. Within weeks, Onnes confirmed the effect was reproducible and measured the critical temperature with remarkable precision.

The Helium Achievement That Made It Possible

Onnes's 1911 breakthrough rested on another monumental achievement three years earlier: in 1908, he became the first person to liquefy helium, reaching temperatures below 4 Kelvin. Helium is the most stubborn of all gases, requiring pressures of 25 atmospheres and temperatures near absolute zero to condense into liquid form. No other laboratory in the world could match Leiden's cryogenic capability at the time, which gave Onnes a monopoly on helium experiments for years.

Once he had liquid helium, he systematically tested the electrical properties of pure metals at these unprecedented temperatures. Mercury was an obvious candidate because it could be purified to extreme levels through repeated distillation, eliminating impurities that might confuse the results. When he measured the resistance of his mercury sample, he expected it to drop gradually toward zero as temperature fell. Instead, at 4.19 Kelvin, the resistance didn't just drop—it disappeared entirely, falling below the detection limit of his instruments. His notebooks record resistance values dropping from 0.1 ohms to essentially zero over a temperature span of just 0.01 degrees.

The Theoretical Mystery and Quantum Solution

For nearly half a century, superconductivity remained a puzzle that stumped the brightest minds in physics. Classical electromagnetic theory predicted that resistance should decrease at low temperatures, but it offered no mechanism for resistance to vanish altogether. The behavior suggested that electrons were acting collectively, moving in coordinated waves rather than bouncing randomly off atoms, but quantum mechanics—the framework that could explain such behavior—was still in its infancy in 1911.

Niels Bohr, Albert Einstein, and Werner Heisenberg all took stabs at explaining superconductivity, but none succeeded. It wasn't until 1957 that John Bardeen, Leon Cooper, and Robert Schrieffer finally cracked the problem with what became known as BCS theory. They showed that at low temperatures, electrons in a superconductor pair up into "Cooper pairs" through interactions with the atomic lattice, allowing them to move without scattering. This breakthrough earned them the 1972 Nobel Prize in Physics. Remarkably, Bardeen became the only person ever to win two Nobel Prizes in Physics—his first came in 1956 for inventing the transistor.

Modern Applications and the Quest for Room Temperature

Today, superconductors power MRI machines in hospitals worldwide, generating the intense magnetic fields needed to image internal organs without harmful radiation. The Large Hadron Collider near Geneva uses 1,232 superconducting dipole magnets cooled to 1.9 Kelvin to steer proton beams at nearly light speed. Maglev trains in Japan float above tracks using superconducting magnets, reaching speeds of 375 miles per hour during test runs in 2015.

Yet practical applications remain limited because conventional superconductors require expensive liquid helium cooling. The discovery of high-temperature superconductors in 1986 by Georg Bednorz and Karl Müller—materials that superconduct at 92 Kelvin, achievable with cheap liquid nitrogen—sparked hopes for revolutionary technologies. In 2020, researchers reported superconductivity at 59°F in a hydrogen-sulfur-carbon compound, though it required crushing pressures of 39 million PSI. The race continues for a room-temperature, ambient-pressure superconductor that could transform power grids, computers, and transportation, turning Onnes's laboratory curiosity into everyday infrastructure.