Yet sound does exist in outer space, where it has a medium. When we measure, from Earth, the light from distant gas clouds, we can sense in them fluctuations of pressure and density, in other words, sound. However, these sounds would be so deep that nobody would be able to hear them; they would be several hundred octaves below the deepest sound humans can hear. Yet the effect of sound is enormous. Indeed, it is sound that creates stars. Shortly after the Big Bang, when material and energy divided, they did so with a resounding noise. And around 4.5 billion years ago, our solar system developed as a result of the sound made by a stellar explosion, which condensed gas and brought heavy elements with it.

In Zvezdny Gorodok, or Star City, not far from Moscow, Yuri Gagarin, from the village of Klushino, once became acquainted with silence. As a cosmonaut, he had to hold out for ten days in a soundproof chamber to get accustomed to being alone and the silence, which he was to bear as the first human being in space. “There was a depth to the silence there like you have never experienced before”, said astronaut Russell Schweickart, recalling his experience outside a capsule. “And it is lonely here in front of the International Space Station, even if someone is floating around near you.” But cosmic silence is more of a thought. You don’t really hear it. Even when, as once happened, a storm cuts radio contact to ground control, it is never totally silent in an astronaut’s suit, because the oxygen supply system and air-conditioning continue to crackle and hiss.

It is likewise incorrect to call what is done here a “space walk”. And not only because it involves nothing of the calm of strolling and there is hardly even time to observe this amazing planet Earth. “Outboard activity” is the term NASA uses for installation and repair work, be it the installation of a tank or repairing a solar sail under the constant danger of getting an electric shock. Somewhere down there on Earth is the Astronaut Memorial Wall, which re - minds you that launches and landings actually involve the greatest risk for space travelers, and yet six hours of work at an elevation of 360 kilometers and a speed of 25,000 km per second are also full of deadly dangers, radiation, several 100 degrees centigrade heat in the sunlight and up to minus 269 degrees in the shade. But what an earlier astronaut once said is also true: “The most difficult thing was going in again afterwards.”

In the aluminum modules, the omnipresent, ongoing sounds of the equipment await: 75 decibels in the working areas and 55 decibels even in the sleeping areas. At least astronauts hardly snore, probably because thanks to weightlessness their tongues do not move and there is better circulation within mucous membranes. But there is music at the ISS, and not only Elton John’s Rocket Man or David Bowie’s Space Oddity.