© ShutterstockScientists have long thought of soundwaves as massless, and this image of the sound waves surrounding a supersonic jet sure look that way. But new research suggests that isn't quite the case.
That's the conclusion of
a paper submitted on July 23 to the preprint journal arXiv, and it shatters the conventional understanding that researchers have long had of sound waves: as massless ripples that zip through matter, giving molecules a shove but ultimately balancing any forward or upward motion with an equal and opposite downward motion. That's a straightforward model that will explain the behavior of sound in most circumstances, but it's not quite true, the new paper argues.
A phonon - a particle-like unit of vibration that can describe sound at very small scales - has a very slight negative mass, and that means sound waves travel upward ever so slightly, said Rafael Krichevsky, a graduate student in physics at Columbia University.
Phonons aren't particles of the sort most people typically imagine, like atoms or molecules, said Krichevsky, who published the paper along with Angelo Esposito, a graduate student in physics at Columbia University, and Alberto Nicolis, an associate physics professor at Columbia.
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