In 1911, Heike Kamerlingh Onnes was cooling mercury inside his Leiden laboratory using newly available liquid helium. At 4.2 Kelvin — about minus 269 Celsius — something happened that did not appear in any textbook. The mercury's electrical resistance dropped to zero. Not very small. Zero.

A current induced in a superconducting loop will continue to flow with no detectable decay for years. Experiments have monitored persistent currents for over a decade and found no measurable loss. Set one going and walk away — it is still going.

The mechanism wasn't worked out until 1957, by Bardeen, Cooper, and Schrieffer. Below a critical temperature, electrons in certain materials pair up — Cooper pairs — bound by a faint distortion of the metal lattice. Pairs behave like a single quantum object. They glide through the metal without scattering, without resistance, without heating.

Superconductors do another strange thing called the Meissner effect: they expel magnetic fields entirely. Drop a small magnet on top of a chilled superconductor and it floats — stably, perfectly — held aloft by an inverted mirror image of itself.

This is not a curiosity. Every MRI machine on Earth uses superconducting magnets to generate the field that maps your soft tissue. Particle accelerators like the Large Hadron Collider use superconducting cables to steer beams. Maglev trains use superconducting electromagnets to glide above the rail.

The catch: today's superconductors only work at extreme cold. The warmest practical superconductor still requires liquid nitrogen. A room-temperature superconductor would transform the world — eliminate transmission losses, enable frictionless transit, revolutionize computing. Physicists have been hunting one for over a century. Several were briefly claimed in 2023. None held up.

The search continues.