In science fiction movies and TV shows, spaceships invariably make a great swooshing sound as they zip by on the screen. During battle scenes the destroyed enemy spaceships explode in a flash of color and sound.
A notable exception is the more realistic movie, 2001: A Space Odyssey. The scientifically correct silence of the space docking scene is filled with the Blue Danube waltz. This background music symbolizes the complex waltz of Newton's Laws in space docking maneuvers.
As satisfying as swooshing sounds are to moviegoers, they are incorrect science. In reality, sounds in space are not possible. To understand why there is no sound in space, it is necessary to first understand what sound is.
What is Sound?
Let a slinky® hang down from your hand to the floor. Now quickly move your hand up and down a few times. Watch the wave traveling through the slinky®. Notice how there are places where the individual wires in the slinky® are compressed more closely together alternating with places where the wires are spread farther apart. Your moving hand created a compression wave traveling through the slinky®. Notice that as this compression wave travels through the slinky®, the individual wires oscillate but do not travel through the slinky®.
A sound wave is a similar compression wave, also called a longitudinal wave. Sound travels through a medium by means of compression waves in the medium. In a gas or liquid, the molecules are alternately squeezed together and spread out as the sound wave travels through the liquid or gas. Just as in the compression wave traveling through a slinky®, the individual molecules oscillate back and forth as they are squeezed together and spread out. These molecules do not, however, travel along as the wave travels through the liquid or gas.
Sound can also propagate through a solid, but it is a little more complex. Sound waves in solids can be compression waves or another type of wave called transverse waves.
Sound Does not Propagate in a Vacuum
The key point about sound waves is that sound waves must travel through some type of medium. The individual atoms or molecules in the medium vibrate to propagate the sound wave.
If there is no medium, there are no atoms or molecules to vibrate and propagate the sound wave. The medium can be a gas, liquid, solid, or plasma (a hot gas in which electrons have escaped from atoms). There must however be a medium to propagate sound waves.
Sound waves can not pass through a vacuum.
Why There Is no Sound in Space
Space is a nearly perfect vacuum. Because sound waves can not pass through a vacuum there can be no sound in space. Space is silent.
A space shuttle launch is very loud when the rocket is still in Earth's atmosphere. Once the shuttle reaches space however it is silent.
As a star ship zips across the universe, it does so perfectly silently. If a starship is destroyed in a space battle, the violent explosion, seen from a safe distance will be eerily silent.
Supernovas are violent explosions of entire stars that release as much energy in about a year as the Sun releases in its 10 billion year lifetime. Astronomers observe the light from these stellar explosions, but never hear them. Light waves travel through space. Sound waves cannot.
Despite the scientific fact that sound cannot travel through space, Hollywood movie makers persist in making spaceships swoosh by the screen. Hollywood science fiction movies usually always get this and much other science wrong. When watching a science fiction movie, be aware of incorrect science, then sit back and enjoy the story.
Paul A. Heckert - I have a Ph.D. in astrophysics, over 30 years experience teaching physics and astronomy, and over 60 published research articles.
