In which environment can sound not travel?

Sound requires a medium to travel, such as solids, liquids, or gases, because it propagates through the vibration of particles within these substances. In a vacuum, however, there are no particles to transmit sound waves. This absence of matter means that sound cannot propagate at all. Hence, in a vacuum, sound does not exist.

In contrast, sound travels effectively through air, water, and solid materials because these media contain particles that can vibrate and transmit the sound waves. Each medium has different properties that can affect the speed and quality of sound transmission, but all of them enable sound to travel, unlike a vacuum where sound is completely absent.