Using two dimensionless fundamental constants, an international team of physicists has calculated the fastest possible speed of sound in condensed phases (solids and liquids): 36 km per second (22.4 miles per second).
Trachenko et al. show that a combination of two dimensionless fundamental constants results in a new dimensionless constant that provides the upper bound for the speed of sound in condensed phases. Image credit: Gerd Altmann.
Waves, such as sound or light waves, are disturbances that move energy from one place to another.
Sound waves can travel through different mediums, such as air or water, and move at different speeds depending on what they’re traveling through.
For example, they move through solids much faster than they would through liquids or gases, which is why you’re able to hear an approaching train much faster if you listen to the sound propagating in the rail track rather than through the air.
Albert Einstein’s theory of special relativity sets the absolute speed limit at which a wave can travel which is the speed of light, and is equal to about 300,000 km per second (186,000 miles per second).
However, until now it was not known whether sound waves also have an upper speed limit when traveling through solids or liquids.
“Sound waves in solids are already hugely important across many scientific fields,” said co-author Professor Chris Pickard, a physicist in the Department of Materials Science and Metallurgy at the University of Cambridge and the Advanced Institute for Materials Research at Tohoku University.
“For example, seismologists use sound waves initiated by earthquakes deep in the Earth interior to understand the nature of seismic events and the properties of Earth composition.”
“They’re also of interest to materials scientists because sound waves are related to important elastic properties including the ability to resist stress.”
In new research, Professor Pickard and his colleagues found that predicting the upper limit of the speed of sound is dependent on two dimensionless fundamental constants: the fine structure constant and the proton-to-electron mass ratio.
The researchers tested their theoretical prediction on a wide range of materials and addressed one specific prediction of their theory that the speed of sound should decrease with the mass of the atom.
This prediction implies that the sound is the fastest in solid atomic hydrogen.
However, hydrogen is an atomic solid at very high pressure above 1 million atmospheres only, pressure comparable to those in the core of gas giants like Jupiter.
At those pressures, hydrogen becomes a fascinating metallic solid conducting electricity just like copper and is predicted to be a room temperature superconductor.
Therefore, the scientists performed state-of-the-art quantum mechanical calculations to test this prediction and found that the speed of sound in solid atomic hydrogen is close to the theoretical fundamental limit.
“Our result expands the current understanding of how fundamental constants can impose new bounds on important physical properties,” they said.
The study was published in the journal Science Advances.
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K. Trachenko et al. 2020. Speed of sound from fundamental physical constants. Science Advances 6 (41): eabc8662; doi: 10.1126/sciadv.abc8662
This article is based on a press-release provided by the Queen Mary University of London.
Source link: https://www.sci.news/physics/sound-speed-limit-08946.html
