Focus: Sound Waves Carry Mass
"..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."
"For a 1-second-long, 1-watt sound wave in water, the amount of mass would be about 0.1 milligrams."
"The new calculation indicates that for ordinary sound waves in most materials, the mass carried is equal to the sound wave energy multiplied by a factor that depends on the speed of sound and the medium’s mass density. And the mass carried by sound waves turns out to be negative. It is a depletion of mass, rather an addition of mass. So sound waves in a gravitational field should float upward somewhat, like any buoyant object in water."
"The researchers hope the effect might be detectable soon. For example, they estimate that the mass carried by a sound wave in a Bose-Einstein condensate of extremely cold atoms could carry as much as 1 part in 1000 of the total mass of the system, near the limits of current detection techniques. More ambitiously, earthquakes generate strong sound waves traveling through Earth’s crust, and the mass associated with them could be as large as 100 billion kilograms, which could register in sensitive gravitational monitoring devices."
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