Naturally, he got a little nervous and decided to take a look through the porthole of the ship, but could not find an explanation for the mysterious blow. Try as he might, he could not decipher what it was.2

Sound waves propagate mechanically as a vibration and therefore need a medium - liquid, solid or gaseous - to travel.
Simple examples would be the sound of the thunder that travels in the air or the sound of the sonar that makes it under the water.

"While interplanetary (and interstellar) space is not completely empty, gas molecules and dust grains are so scattered that they do not form a continuous medium that allows sound waves to be transmitted directly," he explained to the academic site The Conversation Professor Monica Grady, Department of Planetary and Space Science at the Open University of the United Kingdom.


Yang revealed his hypothesis about what happened: the sound was the product of the reduction of the air pressure that caused changes in the structure of the spacecraft as it left the Earth's atmosphere and entered space, Xinhua news agency reported.

He added that air escaping from objects within the space capsule could also cause sound.