Nicola Baird, of Stirling School, asks :-

Do sounds echo in space?

John Campbell, a physicist at the University of Canterbury, responded.

No. Sound waves travel only in matter and so cannot travel through space.

When you hit a saucepan, for example, the atoms in the metal saucepan vibrate. This vibration causes air molecules next to the pan to vibrate and they in turn cause their neighbouring molecules of air to vibrate. Hence the sound travels to us through the air.

Because it depends on the molecules present and the forces between them, sound travels at different speeds in different materials, for example 330 metres every second in air, 1400 metres every second in water and 5100 metres every second in aluminium.

Because space is essential empty of molecules there is nothing in space to vibrate and so sound does not travel and hence there can be no echoes in space. However if a person in space held their helmet against a metal wall and tapped the wall they would hear echoes because the sound wave travelling in the metal would be reflected at the far end of the metal.

So next time you see a movie or TV programme involving space, remember that many of the sound effects are not possible in practice. For example, Superman cannot talk directly to a spacewalker and all those explosions in space would be noiseless to an astronaut not in touch with the exploding object or in radio contact with instruments on it. Moviemakers add lots of noise to the soundtrack to add excitement not reality.