What we are used to calling the “speed of sound” is actually the speed that sound waves reach in air, at a temperature of 20°C: approximately 343 meters per second. But this can vary depending on temperature and material. For example, at an atmospheric temperature of -10 °C, the speed drops to 325 m/s, while in aluminum it rises to 6.320 m/s.
Research carried out at Queen Mary University of London, in partnership with the University of Cambridge and the Institute for High Pressure Physics in Troitsk, Russia, found the fastest possible speed of sound: 36 meters per second.
Sound waves, or any wave, are disturbances that move energy from one place to another. The speed of this movement depends on the medium through which the wave is travelling. In the case of sound, it moves faster through solids than through liquids or gases. The more rigid the medium, the faster the sound travels.
This is why, for example, you can hear a train approaching much faster if you put your ear close to the tracks. For the same reason, whales are able to bond over long distances in the ocean, as water is more peaceful than air.
An F-15E Strike Eagle breaks through the sound barrier during a training exercise. Image: US Air Force / Airman 1st Class Lauren M. Johnson
Until now, the highest speed recorded for sound was 12 meters per second, the wave passing through a diamond. The new number, however, is more than double that. It is impossible to measure the speed of sound in all existing materials, but scientists have managed to establish a limit based on the fundamental constants, the universal parameters by which we understand the physics of the universe.
Einstein's theory of special relativity sets the absolute speed limit at which a wave can travel, which is the speed of light, at about 300 kilometers per second. The new study, published in the journal Science Advances, shows that predicting the upper limit of the speed of sound depends on two fundamental dimensionless constants: the fine structure constant and the proton-to-electron mass ratio.
These two numbers are known to physicists. They govern nuclear reactions, proton decay and nuclear synthesis in stars. The balance between them provides a narrow "habitable zone" where stars and planets can form and life-supporting molecular structures can emerge.
The scientists tested the influence of these two constants on a wide variety of materials and addressed a specific prediction of their theory that the speed of sound should decrease the mass of the atom. This prediction implies that sound travels faster through solid atomic hydrogen.
The problem is that for the element to reach this point, a pressure above a million atmospheres is needed – the same in the core of gaseous giants, Jupiter. In this environment, hydrogen becomes a superconducting metallic solid. Starting from this premise, the researchers performed state-of-the-art quantum mechanical calculations and found that the speed of sound in solid atomic hydrogen is close to the fundamental theoretical limit.
“The calculation of sound waves in solids is already extremely important in many scientific fields. For example, seismologists use sound waves initiated by earthquakes in the Earth's interior to understand the seismic nature of certain events and the properties of the Earth's position." of the study.
Via: ScienceAlert
