Mark Megahan
The assumption that sound can’t cross a vacuum has been shattered. even so, it’s still true that in space, nobody can hear you scream. The conditions have to be exactly right and the concept hinges on the fact that even a perfect vacuum isn’t “empty.” Zhuoran Geng and Ilari Maasilta of the University of Jyväskylä in Finland are convinced that “their findings represent the first rigorous proof of complete acoustic tunneling.”
Sound can tunnel through space
Under some very special circumstances, “it is possible for sound to travel through a perfect vacuum.” Geng and Maasilta worked out exactly what those conditions needed to be, fed them into their finite probability generator, poured in some nice hot tea and out popped “two piezoelectric materials, which are capable of turning movements into voltages.”
Two because they work in pairs, as sender and receiver. You can’t just stick them just anywhere. They’re still totally useless for one of those “open the pod bay doors, Hal” kind of moments. “The objects need to be separated by a gap that’s smaller than the wavelength of the sound you want to send.”
The freaky part, and it has quantum physicists paying close attention, is the way a sound can “completely jump – or ‘tunnel‘ – across that space.” It’s really nothing new, the scientists modestly downplay.
“We’ve known about acoustic wave tunneling since the 1960s, but scientists have only begun to investigate the phenomenon relatively recently, which means we don’t yet have a very good understanding of how it works.” Geng and Maasilta “have been working on fixing that.”
They basically needed to start from the ground up by “describing a formalism for the study of acoustic tunneling.” Now, they’re at the stage of putting their theories to the test. They knew that “sound requires a medium to travel through” because it’s “generated by vibrations, which causes atoms and molecules in the medium to vibrate.”
When a particle gets bumped, it bumps it’s neighbor. Eventually our ears pick up the vibrations as they travel through air. Things get funkier than George Clinton when you try to do it in the “complete absence of a medium.” A perfect vacuum has no particles to vibrate.
Loopholes in the laws of physics
The only laws which can’t be broken are the laws of physics but they do seem to have a few “loopholes” and this is one of them. “What qualifies as a vacuum can still buzz with electrical fields, which makes piezoelectric crystals an intriguing material for the study of sound across otherwise empty spaces.”
They’re what are known as “transducers” and work like a microphone and speakers. If “you place a mechanical stress on the crystal, it will produce an electric field. And if you expose the crystal to an electrical field, the crystal will deform. That’s known as the inverse piezoelectric effect.”
A sound vibration “exerts mechanical stress” and crystals of zinc oxide can convert the stress to an electrical field. In order for a second crystal of the same substance to convert the electrical field back to a mechanical one, it must be within “range” of the first.
It works, even in the nothingness of deep space, when the gap is “no wider than the length of the initial acoustic wave.” The good news is that the effect “scales with frequency.” That means “even ultrasound and hypersound frequencies can tunnel through the vacuum between the two crystals.”
While that doesn’t sound very earth-shattering to most humans, quantum physics majors are picking new topics for their thesis. “Because the phenomenon is analogous to the quantum mechanical effect of tunneling, the results of the research could help scientists study quantum information science, as well as other areas of physics.”
The modest researchers admit that “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, without any reflections.” What that means, Dr. Maasilta explains is, “as such, the phenomenon could find applications in microelectromechanical components (MEMS, smartphone technology) and in the control of heat.“
