# How fast can you throw Coldplay’s X&Y album?

(Because, you know, it’s an article about how fast sound can theoretically travel…and Coldplay has a song called “Speed of Sound”…and it’s on the X&Y album…I’ll stop now.)

ANYWAY.

So we all know about the speed of light, right? According to Einstein’s theory of special relativity, the fastest a wave can possibly travel is about 300,000 km/s: the speed of light. But what about sound? That is, is there an “upper limit” to the speed of a sound wave? Well, turns out there is.

In general, sound waves travel faster through solids faster than they do through gases or liquids. For example, sound travels through a diamond about 35 times faster than it does through air. That’s about as fast as sound can normally go. But how fast could it theoretically go?

Scientists at Queen Mary University and University of Cambridge theorized that the speed of sound should decrease with the mass of the atoms in a substance, meaning that sound should be fastest through solid hydrogen. They couldn’t actually physically test this, though, as hydrogen becomes a solid only under very, very high pressure (like +1 million atmospheres) that cannot be replicated on earth (yet). So they basically did a bunch of quantum mechanical calculations to see what the result should be and found that yes, the speed of sound in solid hydrogen is close to the theoretical limit of the speed of sound.

So that’s pretty cool!