Conventional wisdom in physics dictates that sound waves are massless fluctuations in pressure that travel through materials like air, water, and eardrums — and can't travel through empty space.
That's why the recent discovery that sound waves actually do carry a trace amount of mass is so shocking — it's been right under scientists' noses for centuries. Even more surprising, according to Scientific American's reporting on the finding, is that sonic waves seem to carry negative mass: they appear to slowly drift upwards rather than falling down to Earth.
Previous research by one of the same scientists first found this negative gravity phenomenon, but only when the sound was traveling through specific materials called superfluids, through which waves can flow with zero resistance. But in this new study, physicists calculated that sound waves can also carry mass through more conventional liquids, as well as solids and gases.
If this research holds up to further scrutiny, it could mean that physicists were wrong about something thought to be so simple that it's taught in middle school science classes.
But replicating this new finding could prove difficult — Scientific American reports that modern technology isn't sensitive enough to measure the minuscule amounts of mass that a sonic wave can carry. As a result, the scientists aren’t sure themselves how the mass of the phonons flows along with the wave.
READ MORE: Sound by the Pound: Surprising Discovery Hints Sonic Waves Carry Mass [Scientific American]