Matt Seal

In 1938, 2 physicists shined a light on liquid helium, and it shot up out of the bath like a fountain. John Allen and Harry Jones had stumbled onto one of the strangest liquids ever found. Years later, physicist Alfred Leitner recreated their fountain on film, along with everything else this liquid can do. Helium turns liquid at 4.2 degrees above absolute zero, about −269°C. Even then it's odd. It weighs only about 1/8 as much as water, and it bends light so little that its surface is almost invisible. It takes just 5 calories to boil away a gram of it, compared with roughly 540 for water. And no matter how cold it gets, it won't freeze unless you squeeze it under high pressure. To cool it further, you pump away the vapor above it. It's brutally slow. More than a third of the liquid has to boil off before the rest reaches the magic temperature, about 2.17 degrees above absolute zero, called the lambda point. On camera, the liquid boils harder and harder as it gets close. Then the bubbles stop all at once. It's still evaporating, but it no longer boils. At that moment, its ability to carry heat jumped about a million times, far better than copper or silver. Heat spreads so fast that no bubble has time to form. This new liquid is called a superfluid, and it breaks almost every rule. A cup with a ceramic bottom, riddled with channels about 1 micron wide, held the normal liquid without leaking. Below the lambda point, the helium poured straight through. Its viscosity was too small to measure. But when they spun a copper cylinder in the same liquid, it dragged the helium along and turned a small paddle wheel. Something in it clearly had friction. The explanation is that superfluid helium behaves like 2 liquids mixed together. One part flows with no friction at all and carries no heat. The other part is ordinary: sticky, warm, and dragged along by the spinning cylinder. Then came the fountain. A glass bulb packed with ultra-fine powder sat in the liquid. Leitner shined a lamp on it, warming it slightly. Helium rushed through the powder toward the heat and shot out the top, rising above the level of the bath. The frictionless part flows toward warmth, and the heat itself powers the pump. It also escapes. Leave it in an empty glass and a film just a few hundred atoms thick climbs up the inside wall, over the rim, and down the outside, dripping from the bottom until the glass is empty. The strangest trick was heat moving as a wave. They sent tiny pulses of heat from a heater through the liquid to a sensor 9 centimeters away. Each pulse arrived 4.5 milliseconds later, a clean echo moving at about 20 meters per second. In every other material, heat slowly spreads out. In superfluid helium, it travels like sound. Physicists call it second sound. The 2-liquid picture works as a guide, but the film admits it isn't the full truth. It's 1 quantum fluid that can move in 2 completely different ways at once. Near absolute zero, quantum physics stops hiding in atoms and starts pouring out of the glass.