Everyone knows that in space no-one can hear you scream. After all, do we all remember watching ‘Alien’? More recently, we’ve seen Sandra Bullock floating through a terrifying blank silence in ‘Gravity’. Even SpaceX’s Starman, currently orbiting somewhere above us, wouldn’t be able to hear the voice of David Bowie blasting from his Tesla Roadster. (The soundtrack to the footage was overlaid by engineers on the ground, alas).
But in fact, although we can’t hear anything in space, the traditional way, it’s not actually as silent as we think. In fact, the universe has its own soundtrack, but you need to have the right instruments to listen – it’s pretty mind-blowing! So buckle in for a jet-fuelled journey through the weird and wonderful space sounds. It’s just as trippy as you’d imagine.
Let’s start with the science on Earth. It’s relatively simple, sound is transmitted as a mechanical, physical wave through a medium, such as air or water. This wave then hits the membrane of a drum and the mechanical vibrations push against the molecules of the air. This then jostles other molecules of the air, as well as others beyond them, and so on. Essentially, It’s like an atomic Mexican wave, if only a little more coordinated.
However, in space, the atoms are really far apart. If you can remember from high school, space is quite literally, space. It’s a vacuum with the occasional hydrogen or helium atom and very occasionally, solids, such as cosmic dust, asteroids or planets. This means that the same vibrating drum would still jostle the atoms nearby, but only very weakly. There wouldn’t be enough jostle to create a soundwave that human ears could hear. Basically, it would be a Mexican wave in a nearly empty stadium. So in other words, what we would hear is silence.
That all sounds pretty logical, right? But what about the kinds of sound you can’t hear? For centuries, philosophers have debated the idea that certain sounds only exist in a heavenly realm, inaudible to the human ear. According to ancient Greek philosopher Pythagoras (who you may also remember from high school), the sun, moon and planets all emit their own ‘celestial sounds’ based on their unique orbits.
These space sounds or ‘harmonies’ were in perfect mathematical proportion, just like musical intervals hence the Latin name for the theory, music universalis. Although they existed in a purely theoretical realm, apparently Pythagoras could literally hear them, thanks to the blessings of the Egyptian god, Thoth (yes, really) – he was a pretty mystical guy.
Pythagoras’ theories were later taken up by Renaissance astronomers like Johannes Kepler. Kepler discovered that the velocity of a planet, at certain points in its orbit, could be expressed as a musical interval, for example, a major third, minor fifth or semitone.
Essentially our solar system was a ‘celestial choir’ made up of bass (Saturn and Jupiter), tenor (Mars), alto (Venus and Earth) and soprano (Mercury) voices. With this finding, Kepler figured out something pretty incredible: the dynamics of the solar system mirror, almost perfectly, the laws of musical harmony.
Although astrophysics has moved on quite a bit from mystical resonances and celestial choirs, it’s amazing that some of NASA’s recent research would have sounded (literally) pretty familiar to Kepler. In 2013, when the Voyager spacecraft reached the edge of our solar system, it detected a burst of mysterious electromagnetic waves. These waves could then be played back through a loudspeaker and are definitely audible (at least on Earth), though more than a little creepy. Voyager then proceeded to record sounds from Mars, Jupiter and even the Sun. As soundtracks go, they’re pretty minimal and sparse, but incredibly eerie and beautiful.
So really, being able to hear the harmonies of the universe is just a matter of having the right ultra-sensitive instruments, pointed at the right part of the sky. Easy, right? With the specific equipment on the Voyager, scientists were able to understand space, in terms of sound. In the same way that traditional telescopes allow astronomers to understand it in terms of visible light.
As physicist Janna Levin said, ‘the universe has a soundtrack, and that soundtrack is played on space itself, because space can wobble like a drum.’ Sounds beyond the ear, music beyond the solar system, and spacecrafts beyond Pythagoras’ wildest dreams. It’s paradoxical and perfect all at once. Bowie’s Starman would no doubt be impressed.