Helium never ceases to amaze. Physicists have now heard a quantum-mechanical whistle emanating from two reservoirs of liquid helium-4 that were separated by a perforated membrane.
According to theory, when liquid helium is pushed through a tiny hole at ultracold temperatures, the substance oscillates at a frequency that, when amplified electronically, sounds like a whistle.
Other than confirming a quantum talent first predicted for helium-4 some 40 years ago, the new findings by Emile M.
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