Cavorite, gravity shields, and spindizzy machines are just some of the sci-fi solutions authors have made up to counteract the effects of gravity. But if a new theoretical study turns out to be correct, then you’ll just need sound.
According to the paper, which is yet to be peer-reviewed and is available on arXiv, the statement that sound waves do not transport mass, just energy, is only correct at first approximation. The team claims that sound waves do carry (a tiny) mass, and that’s not all: the mass is negative.
While this claim will definitely raise more than a few eyebrows, it is interesting to look at their work for two reasons: The team put forward not only a theoretical edifice but also a way to test their claim, and their work is based on a recent study from one of the authors.
In that work, published in Physical Review B, the physicists noticed that sound waves coupled with gravity in superfluids, which is a particular state of matter in certain substances at almost absolute zero where the viscosity of the liquid becomes zero so the liquid flows without losing kinetic energy. Superfluids have weird effects, such as the ability to climb up the walls of a container and, based on this research, for sound to float in them.
In the new paper, the scientists have tried to extend the results from the quantum world of superfluids to regular solids and fluids. Interestingly, the negative mass depends on the energy transported by the sound wave and on a coefficient that depends only on the material through which the wave is propagating.
“We showed that, contrary to common belief, sound waves carry gravitational mass, in a standard Newtonian sense: they are affected by gravity, but they also source gravity,” the researchers write in the paper.
The researchers estimate that this effect is tiny, but they state that it could be detected in certain scenarios. Atomic clocks and quantum gravimeters are not quite there yet in terms of sensitivity, but they could soon be able to detect such small effects. The researchers also suggest that it could be possible to setup ultracold atoms in a way to enhance this effect and detect it. There is also the possibility that this negative mass can be seen in extreme environments like inside neutron stars.
The paper is a beginning rather than an end, but it raises a possibility that might have lots of interesting consequences.