Did You Hear That? Scientists Have Finally Discovered the Ultimate Speed Limit of Sound
Screenshot from a video tutorial on sounds uploaded by khanacademymedicine.
Einstein’s theory of special relativity is a standard to study speed limits. It sets absolute speed limits for a wave at 300,000 Km per second which is about the speed of light. But it wasn’t clear whether sound waves would have such an absolute upper limit in their propagation through liquids or solids.
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Sound travels fast, that we know, but how fast can it actually go? Turns out, very, very fast. A new record has been set for the fastest possible speed of sound at 36 km per second. The researchers believed that this speed is twice as fast as sound’s speed in a diamond.
Sound has a property where its speed is influenced by the medium in which it travels. Depending on the density of the medium, it can go faster or slower. It also tends to go faster in solids; therefore, its speed in diamond is understandable as it’s the hardest material known to humans. For a relatable example, when you’re in a train or platform, you can hear the sounds vibrating through the racks much before you can hear it in the air.
Now Einstein’s theory of special relativity is a standard to study speed limits. It sets absolute speed limits for a wave at 300,000 Km per second which is about the speed of light. But it wasn’t clear whether sound waves would have such an absolute upper limit in their propagation through liquids or solids.
The study of sound waves is very important in multiple fields of science. Sound waves from deep in the earth or during earthquakes can be studied by seismologists to know nature of seismic events and the properties of Earth composition.
As for this study, Kostya Trachenko and his colleagues considered two well-known physical constants of the wave. First, the ratio of proton mass to electron mass. Second, the fine structure constant, which illustrates the strength of interactions among charged particles.
According to Trachenko, these values are pretty well-known; as even a slight change in any of them would affect the universe as a whole. “If you change these constants by a few per cent, then the proton might not be stable anymore, and you might not even have the processes in stars resulting in the synthesis of heavy elements, so there would be no carbon, no life,” he said.
With this knowledge in hand, the researchers made a prediction. Solid metallic hydrogen, which is debated by many scientists on being a reliable lab material but is present in the centre of many gas planets, must have the highest speed of sound. Their calculations put it around the theoretical limit.