Trio of Columbia University scientists discoverednew evidence that sound waves carry mass. In their article published in the journal Physical Review Letters, Angelo Esposito, Rafael Krichevsky and Alberto Nicolis described the use of effective field theory methods to confirm the results obtained by the team last year when they tried to measure the mass transferred by sound waves.
Sound carries weight. Why is it important?
For years, physicists were convinced thatSound waves carry energy, but there is no evidence that they carry mass. It seemed there was no reason to believe that they would generate a gravitational field. Last year, this changed because Nicolis and another physicist Riccardo Penco dug up data suggesting that the traditional concept might be wrong. They used quantum field theory to show that sound waves moving in superfluid helium carry a small amount of mass with them. More specifically, they found that the phonons interacted with the gravitational field in such a way that they were forced to carry away mass as they moved through the medium. In the new work, scientists reported that similar results are true for most materials.
Using effective field theory, they showedthat a one-watt sound wave that moved in water for a second carries a mass of approximately 0.1 milligram. They also note that this mass was part of the total mass of the system, which moved with the wave, because it moved from one place to another.
It is important to note that the researchers are not actuallymeasured the mass carried by the sound wave — they used mathematics to prove that it was happening. In the case of real measurements, they suggested experiments that can be performed with sound waves in Bose-Einstein condensate from very cold atoms — such an installation should show enough portable mass to be measured. They also note that the best approach would be to measure the mass carried by sound waves that pass through the earth as part of an earthquake. Such a sound can carry billions of kilograms of mass, which will become visible on devices measuring the gravitational field.
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