In a vacuum, sound cannot propagate or travel as it does in a medium such as air, water, or solids. Sound is a mechanical wave that requires a medium to transmit its energy. When sound waves reach a vacuum, they cannot propagate further because there are no molecules or particles to transfer the vibrations.
In the absence of a medium, such as in outer space where a vacuum exists, sound waves essentially "die out" or cease to exist. There is no medium to carry the vibrations of the sound, so the wave dissipates and cannot be heard.
It's important to note that sound waves are different from electromagnetic waves, such as light, which can travel through a vacuum. Electromagnetic waves do not require a medium and can propagate through empty space.