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Sound has negative mass, and all around you it's drifting up, up and away — albeit very slowly.

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. [The Mysterious Physics of 7 Everyday Things]

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.

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Category: Science