Scientists Reach the Upper Limit of the Speed of Sound

And it's about twice as fast as the speed of sound in diamond.
Irmak Bayrakdar
The photo credit line may appear like thisPobytov/iStock

A team of researchers from the Queen Mary University of London, the University of Cambridge, and the Institute for High Pressure Physics in Russia has just discovered the fastest possible speed of sound.  

Measuring the sound waves

The study found that pinning down an upper limit to the speed of sound can be made possible by measuring two dimensionless fundamental constants: the fine structure constant and the proton-to-electron mass ratio.

These fundamental constants have been observed to be affecting a wide range of scientific areas, including nuclear reactions and habitable zones in space. Apparently, they can also help us pinpoint the speed of sound.


Researchers tested sound waves with a range of materials in order to find the answer to a specific theory of their own: the speed of sound should decrease with the mass of the atom. According to their prediction, the sound should be fastest in solid atomic hydrogen.

Solid atomic hydrogen 

However, solid atomic hydrogen is very hard to come across, since it only appears in very high pressures above 1 million atmospheres. At those pressures, comparable to those found in the core of gas giants like Jupiter, hydrogen forms a metallic solid; similar to copper, and is predicted to act as a room-temperature superconductor. 

The researchers used quantum mechanical calculations to calculate that the speed of sound in solid atomic hydrogen should be around the theoretical fundamental limit. 

According to the University of Cambridge, the study result is about 22 miles (36 km) per second. That is around twice as fast as the speed of sound in diamond, the hardest known material in the world.

Professor Chris Pickard, from Cambridge's Department of Materials Science and Metallurgy, explained that "Soundwaves in solids are already hugely important across many scientific fields. For example, seismologists use sound waves initiated by earthquakes deep in the Earth's interior to understand the nature of seismic events and the properties of Earth's composition." 

Professor Kostya Trachenko, Professor of Physics at Queen Mary added, "We believe the findings of this study could have further scientific applications by helping us to find and understand limits of different properties such as viscosity and thermal conductivity relevant for high-temperature superconductivity, quark-gluon plasma, and even black hole physics."


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