“Sound travels fastest in a vacuum.”

Many people mistakenly believe that sound can travel, or even travel fastest, in a vacuum, perhaps drawing a parallel with light which effortlessly traverses the emptiness of space. This misconception may also have roots in early scientific endeavors. For instance, in 1650, Athanasius Kircher conducted a "bell-in-vacuum" experiment where he still heard a bell after pumping air out of a jar, leading him to incorrectly conclude that air wasn't necessary for sound transmission. However, his equipment was likely insufficient to create a true vacuum, a flaw later corrected by Robert Boyle in 1660, who demonstrated the sound diminishing as air was removed.

The scientific truth is that sound is a mechanical wave, meaning it requires a medium—a substance made of particles like air, water, or solids—through which its vibrations can propagate. When an object vibrates, it causes the surrounding particles to bump into each other, transmitting the sound energy. In a true vacuum, there are virtually no particles to create these collisions, effectively making sound propagation impossible. This is why the iconic movie tagline "in space, no one can hear you scream (Review)" is scientifically accurate.

While the general rule holds, recent cutting-edge research has demonstrated a highly specific phenomenon where sound can "tunnel" through extremely small vacuum gaps. This is not regular sound propagation but a quantum mechanical effect observed between piezoelectric materials. In this unique scenario, the mechanical vibrations in one piezoelectric crystal are converted into an electric field that can traverse a minute vacuum gap, then convert back into mechanical vibrations in a second crystal. This specialized interaction does not mean sound generally travels in empty space; it merely highlights a fascinating exception under very controlled and microscopic conditions.