Sound Cannot Travel Through Space

The roar of a starship engine or the boom of an exploding planet are common tropes in science fiction, but they are purely cinematic creations. Sound as we experience it is a mechanical wave, a form of energy that needs to travel by making molecules vibrate. These vibrations are passed from particle to particle, like a ripple in a pond, through a medium such as air, water, or a solid object. Outer space, however, is a near-perfect vacuum. While not completely empty, its particle density is incredibly low, with vast distances separating individual atoms and molecules. There simply aren't enough particles to collide and carry the vibrations of a sound wave.

The understanding that sound requires a medium was solidified in the 17th century through a classic experiment. Scientists like Robert Boyle placed a bell inside a glass jar and pumped out the air to create a vacuum. As the air was removed, the ringing of the bell grew fainter until it became completely inaudible, even though the bell was still visibly vibrating. This demonstrated that without a medium like air to travel through, the sound waves had no way to reach the observer.

This is why astronauts communicating on a spacewalk rely on radios in their helmets, which transmit electromagnetic waves that can travel through a vacuum. Interestingly, some sound waves do exist in the sparse gas between stars and galaxies, but their wavelengths are so vast and their frequencies so low—well below the range of human hearing—that the cosmos remains a profoundly silent place to our ears.