In 2018, a trio of researchers at Columbia University proposed that sound waves—just … ordinary sound waves—might generate negative gravity. That theory, covered in phys.org, has to do with something called a “phonon.” The phonon (not photon) is a concept from quantum mechanics that represents an elementary unit of vibrational motion. In terms that would surely drive a quantum physicist to distraction, it might be thought of as the smallest possible “particle of sound.”
As with photons and light waves, sound waves (or any “excitation”) within matter may display both wave-like and particle-like behaviors. And as with all things quantum, there are fixed scales at which things not only do, but can, occur. But while phonons may be “particle-like” physicists have generally treated this behavior as a kind of convenience for dealing with how sound interacts with other forces. It hasn’t been treated like a “real particle.”
But the Columbia researchers did the math on what it would mean if a phonon was more than just particle-like, and out of the math from that theory sprang a prediction that phonons would interact with gravitational fields to produce negative-mass and negative-gravity. Unfortunately, the predicted phenomenon would be very difficult to detect using current technology. Except … as the March edition of Physics reports, the three researchers have extended their math, and found that the theory applies to sound waves traveling through materials like liquids and solids, which means it potentially can be detected. …