The sound quality is negative, rising slowly around you, though slowly. This is the conclusion of a paper, which breaks the traditional understanding of sound waves for a long time: massless waves pass through matter and give molecules a thrust, but eventually any forward or upward motion is balanced by equal or opposite downward motion. This is a simple and clear model, which can explain the behavior of sound in most cases, but it is not completely correct. Rafael Krichevsky, a physics graduate student at Columbia University, said: Phonon is a vibration unit, which can describe the sound similar to particles on a very small scale-it has a very slight negative mass, which means that sound waves travel very slowly.

Boko Park-Popular Science: Krichevski, who co-published this paper with Angelo Esposito, a graduate student of physics at Columbia University, and Alberto Nickless, an associate professor of physics at Columbia University, said: Phonons are not particles that most people usually think of, such as atoms or molecules. When sound propagates in the air, it will make the surrounding molecules vibrate, but this kind of vibration is difficult to be described by the movement of the molecules themselves. On the contrary, just as light waves can be described as photons or particles of light, phonons are a way to describe the complex interaction of fluid molecules to produce sound waves. No physical particles appear, but researchers can describe it with the mathematics of particles.

The researchers found that the mass of these emerging phonons is very small, which means that when gravity "pulls" them, they will move in the opposite direction. In the gravitational field, phonons will slowly accelerate in the opposite direction, just like bricks. To understand how this works, imagine gravity acting down on a normal fluid. Fluid particles will compress the particles below, so the density below will be slightly higher. Physicists have known that the speed of sound propagation in a dense medium is usually faster than that in a less dense medium, so the speed of sound above a phonon is slower than that below a slightly denser phonon, which causes the phonon to "deflect" upwards. This process also happens in large-scale sound waves, which includes all the sounds that come out of your mouth-although only very slightly. In a long enough distance, your voice saying "hello" will bend upward into the sky.

The researchers wrote in a new paper without peer review that this effect is too small to be measured by existing technology. However, it is not impossible to detect the tiny bend of phonon path with ultra-precision clock in the future. (In its original report on heavy metal music, New Scientist suggested that heavy metal music would be an interesting candidate for this kind of experiment. The researchers wrote that this discovery does have some consequences. In the dense neutron star core, sound waves move at a speed close to the speed of light, and anti-gravity sound waves should have a real impact on the behavior of the whole star. However, for the time being, this is completely theoretical-it is worth pondering when the voices around us are rising day by day.