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Massive sound. A small amount of mass is transported along with all sound waves, according to a new theory.

March 1, 2019• Physics 12, 23
Even if you ignore general relativity, sound waves transport a small amount of mass, according to theory.

Ordinary sound waves carry a small amount of mass with them as they travel, according to a new theoretical study. The theory assumes Newtonian conditions, so the effect is unrelated to either quantum theory or the equivalence of energy and mass known from relativity. The researchers do not yet have a clear physical explanation of their mathematical results, but they say that the idea should be testable in experiments with ultracold atoms, or possibly in observations of earthquakes.

Last year, high-energy physicists Alberto Nicolis of Columbia University in New York and Riccardo Penco, now at Carnegie Mellon University (CMU) in Pittsburgh, used quantum field theory to analyze the behavior of sound waves moving through superfluid helium [1]. To their surprise, they found that the waves carry a small amount of mass, not only by virtue of Einstein’s famous formula equating energy with mass. The duo found that phonons, the quantum units of sound waves, interact with a gravitational field in a way that requires them to transport mass as they move.

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