A joint study by the University of London, Cambridge University, and the Troitsk Institute for High-Pressure Physics has calculated the maximum possible speed of sound. Their result, about 36 kilometers per second, is about twice the speed of sound in diamond, the hardest material in the world.
The researchers explained that waves are vibrations that move energy from one place to another. Sound waves can travel through different media, such as air or water, and travel at different speeds depending on what they are passing through. For example, they travel through solids much faster than through liquids or gases, so you can hear an approaching train much faster if you listen to the sound traveling along the rails rather than through the air.
Einstein’s theory of special relativity sets the absolute speed limit at which a wave can move at the speed of light, and is equal to about 300 thousand km per second. However, until now it was not known whether a sound wave has an upper-speed limit when moving through solids or liquids.
The study, published in the journal Science Advances, shows that the prediction of the upper limit of the speed of sound depends on two dimensionless fundamental constants: the fine structure constant and the proton-to-electron mass ratio.
It is known that these two numbers play a key role in many processes of the Universe: the course of such reactions as the decay of a proton and nuclear fusion in stars depends on their value, and the balance between these two values sets a narrow corridor of the “habitable zone” where planets and life-supporting molecular structures emerge.
The authors suggested that the speed of sound should decrease with increasing atomic mass. According to this theoretical prediction, which scientists have tested on a wide range of materials, the fastest sound will be in solid atomic hydrogen.
“Sound waves in solids are important in many areas of science,” said co-author Chris Picard, professor of materials science at the University of Cambridge. “For example, seismologists use sound waves caused by earthquakes to understand the nature and internal structure of the earth. They are also of interest to materials scientists because they determine the elastic properties of materials, their ability to withstand loads”.