Physicists Figure Out a Novel Way to Let Sound Travel Through Space

Piezoelectric materials can transmit sound across a vacuum by converting it into an electric field.

American actress Sigourney Weaver in the role of Ripley in the film 'Alien'.   (Photo by Hulton Arch...
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Finally, someone can hear you scream in space.

Sound waves can’t travel through the vacuum of space, but a pair of physicists in Finland have found a sneaky way to transmit sound across the airless void, at least for short distances. The method relies on piezoelectric materials to convert sound waves into an electric field to cross the vacuum, then convert the electric field back to sound waves on the other side. They say the technique might be useful in a surprising set of applications here on Earth.

The physicists published their work in the journal Communications Physics.

Screaming Across the Void

It happens to all of us eventually: you’re trapped on a spaceship with a dangerous alien, your whole crew is dead, and you really want to scream — but sound can’t travel through space, so no one could hear you anyway. What’s a sci-fi/horror protagonist to do?

The answer is science. The answer is always science.

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The sounds you hear are just vibrations passing through the air around you. A sound’s pitch depends partly on the density of the air that’s vibrating, which means an open-air concert on Mars or Venus would sound very different from one here on Earth. Without air, there’s nothing to vibrate, and therefore no sound. That’s why explosions in space are eerily silent.

But a group of physicists says they’ve found a way around that pesky rule.

Zhuoran Geng and Ilari Maasilta from the Nanoscience Center at the University of Jyväskylä say the trick is to pass sound waves through a special type of material, called a piezoelectric material. These materials include crystals like tourmaline and quartz, certain types of ceramics and polymers, and some semiconductors like zinc oxide. What’s special about piezoelectric materials is how they respond to stress: they produce electrical voltage when they’re pressed, bent, stretched, or vibrated.

So make sure you’re standing right next to a piezoelectric hull plate before you scream. The sound will cause the air to vibrate, and those vibrations will pass through the piezoelectric plate and produce an electric field. Undeterred by vacuum, the electric field will push and pull nearby charged particles — like the ones in a second piezoelectric plate on the other side of a vacuum. In other words, the electric field transmits the vibrations of your scream across a vacuum to another piezoelectric material, which translates them back into sound waves.

“In most cases, the effect is small, but we also found situations where the full energy of the wave jumps across the vacuum with 100 percent efficiency,” say Geng and Maasilta in a recent statement.

There’s a catch, of course. The gap between the two piezoelectric materials has to be smaller than the wavelength of the sound waves being transmitted. For the average human scream, that’s somewhere between 3 and 38 feet (the deepest sounds a human can hear have wavelengths of about 56 feet, and the highest have wavelengths of less than an inch).

In the real world, Geng and Maasilta say their method could be useful in tiny systems that combine electrical and mechanical parts, like some types of sensors, or even to help control temperature (other teams of engineers have experimented for several years with ways to use sound waves to move heat).