Researchers Just Found The Upper Limit For The Speed Of Sound In The Universe

An international research collaboration has discovered the fastest possible speed of sound. The upper limit was found to be about 36 km per second. For a perspective, this speed is around twice as fast as the speed of sound in diamond, the hardest known material in the world.

The research was a collaboration between the Queen Mary University of London, the University of Cambridge and the Institute for High Pressure Physics in Troitsk. The researchers published a paper describing this upper limit in Science Advances journal recently.

Sound and its Speed
Sound waves are basically disturbances that move energy from one place to another. We know that sound travels through different medium at different speeds. For example, it moves through solids much faster compared to liquids or gases.

We know that theory of relativity puts an upper limit on the speed of light which is 300,000 km per second but interestingly we did not know whether sound waves also have an upper-speed limit when travelling through solids or liquids.

To find that upper limit, researchers showed that predicting the upper limit of the speed of sound is dependent on two dimensionless fundamental constants, namely:

1. The fine structure constant, also known as Sommerfeld’s constant.
2. The proton-to-electron mass ratio.

The values of these two constants are already known to us. These fundamental constants already play an important role in the understanding of our Universe.

Researchers addressed one specific prediction of their theory that the speed of sound should decrease with increasing mass of the atom. This obviously implies that the speed of sound is the highest in solid atomic hydrogen. Therefore, researchers 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.

Recent findings suggest that these constants can also influence other scientific fields, such as materials science and condensed matter physics, by setting limits to specific material properties such as the speed of sound.

Journal Reference:
K. Trachenko, V. V. Brazhkin, C. J. Pickard, B. Monserrat. Speed of sound from fundamental physical constants Science Advances (2020) advances.sciencemag.org/content/6/41/eabc8662