Fundamental constants place a new speed limit on sound

Sound has a speed limit. Under normal circumstances, its waves can travel no faster than about 36 kilometers per second, physicists propose October 9 in Science Advances.

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A very interesting article, quite a bit there to reflect on.

Thanks TN, it is very interesting (although why finance broker should be interested, I don’t know).

Also London University Queen Mary College (as it was then) is where I did my first degree.

Tau.Neutrino said:

Fundamental constants place a new speed limit on sound

Sound has a speed limit. Under normal circumstances, its waves can travel no faster than about 36 kilometers per second, physicists propose October 9 in Science Advances.

more…

> The fastest speed measured, in diamond, was only about half the theoretical maximum.

Diamond. Now there’s a surprise. I would not have guessed that that was the fastest measured speed.

> The limit applies only to solids and liquids at pressures typically found on Earth. At pressures millions of times that of Earth’s atmosphere, sound waves move faster and could surpass the limit.

Indeed. In metallic hydrogen (eg. inside Jupiter), degenerate matter (white dwarfs), neutronium (neutron stars), and quark matter (neutron stars), I would expect the speed to be larger. Possibly even in the cores of red dwarfs (compressed ionised hydrogen).

Here’s a question: What is the speed of sound in black holes?

From article. https://advances.sciencemag.org/content/6/41/eabc8662

Here v _u is the speed of sound, alpha is the fine structure constant, m _p is the mass of a proton and c is the speed of light.

What does the mass of a proton have to do with it … oh, I see … it plays a role because material density plays a role and because proton mass is the dominant component of material density.

Note that they’re actually dropping a factor of 2 in Equation 2. So the maximum speed of sound can be twice this.

Look at this graph. Their Figure 1. Diamond is the highest blue dot (experimental measurement) on the graph. The vertical scatter of the blue dots tells us that for hydrogen, the limiting speed of sound of 36 km/s could perhaps be too small by up to a factor of 2, in line with their Equation 2.

An interesting piece of work.