Sound cannot travel through a vacuum because there are no particles to transmit the vibrations. When sound waves encounter a vacuum, they cannot propagate, leading to a complete absence of sound in that environment. The energy of the sound wave is not lost but instead is reflected back if it encounters a boundary. Shock waves and other phenomena can exist in different mediums, such as nebulae, where sound can interact with particles. Understanding sound in a vacuum highlights the importance of a medium for sound wave transmission.