Suppose you could freeze the water in a washing machine while it was operating. Once the water had solidified, the machine’s agitators would cause the entire icy mass to oscillate—until the motor burned out. In January of this year, Eun-Seong Kim and Moses Chan, both at Pennsylvania State University, reported an experiment 1 that has some of the flavor of the washing-machine fantasy, but which yielded a surprising result (see Physics Today, Physics Today 0031-9228 574200421 https://doi.org/10.1063/1.1752411 April 2004, page 21 ). They introduced liquid helium-4 into a torsional oscillator, solidified the liquid at high pressure, and lowered the temperature. When the temperature fell below about 175 mK, the period of the resonant oscillation also began to fall. About 1% of the 4He in the oscillator appeared not to move with the bulk oscillation; it behaved as a superfluid would.

The 4He, though, was...

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