Superconductivity is a phenomenon where certain materials lose all electrical resistance when cooled to near absolute zero. Helium has a bizarre reaction to cooling—at its critical temperature of 2.17 Kelvin (-271 Celsius), otherwise known as its “lambda point”, it undergoes a transformation from gas to liquid. A fraction of the helium atoms are condensed to the lowest possible energy, so they all have the same momentum—if one moves, they all move. The liquid then becomes a superfluid, which is state of zero viscosity (zero resistance to flow). The helium can no longer be held, because it’s able to flow freely without friction to impede it—it pours through tiny gaps, even through thin capillary tubes or through the microscopic pores of beakers; it defies gravity and flows up walls—a vertical tube can become a fountain of superfuid helium—and if the superfluid is set in circular motion, it keeps flowing around forever. The properties are mind-boggling, like a macroscopic manifestation of quantum mechanics—but superfluids aren’t only found in laboratories. NASA’s Chandra X-Ray Observatory has found exotic superfluid in the ultra-dense heart of a rapidly-cooling neutron star, Cassiopeia A.
Watch a video of superfluid helium (4:12)