The upper limit of the speed of sound is determined

For the first time, British and Russian physicists calculated the maximum possible speed of sound – 36 kilometers per second. This is roughly double the speed of sound in diamond, the hardest known material in the world. The research results are published in the journal Science Advances.

Einstein’s special theory of relativity sets an absolute limit on the speed with which a wave can travel. It is equal to the speed of light – about 300 thousand kilometers per second. However, until now it was not known whether sound waves have an upper limit on the speed.

The speed of sound is determined by the elasticity and density of the medium; it is less in gases and liquids, and more in solids. Therefore, putting your ear to the rails, you can hear the approaching train much earlier than the noise from it comes through the air.

Scientists from Queen Mary University of London, Cambridge University and the Troitsk Institute for High Pressure Physics have calculated the maximum possible speed of sound based on two dimensionless fundamental physical constants: the fine structure constant and the mass ratio of a proton and an electron.

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.

In the core of gas giants such as Jupiter, where pressures exceed one million atmospheres, hydrogen is solid, a metal with superconducting properties. Having performed complex quantum mechanical calculations, the authors determined that the speed of sound in solid atomic hydrogen is close to the theoretical fundamental limit.

“Sound waves in solids are important in many areas of science,” said co-author Chris Pickard, a professor of materials science at the University of Cambridge, in a press release from Queen Mary University of London. “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 stress. ”

The authors believe that the results of the study will also have serious scientific applications, in particular, they will help to find the limits of such physical parameters as viscosity and thermal conductivity used in theoretical calculations related to high-temperature superconductivity, quark-gluon plasma and the physics of black holes.

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