Sound, as we know it, relies on a medium to propagate. Typically, it travels through particles in a medium, such as air or water, by causing them to vibrate. This fundamental principle has led to the common belief that sound cannot exist in the vacuum of space, where there is an absence of particles for sound waves to interact with. The famous line, "In space, no one can hear you scream," from the 1979 sci-fi film "Alien," is a testament to this notion.
However, the research conducted by Zhuoran Geng and Ilari Maasilta challenges this long-standing assumption. In a groundbreaking development that challenges conventional wisdom, researchers from the University of Jyväskylä in Finland have demonstrated the possibility of sound traveling through a vacuum. This extraordinary achievement, detailed in a study published in the journal Communications Physics on July 15, 2023, could have far-reaching implications for various fields of science and technology.
Their work centers around the intriguing concept of "acoustic tunneling" in a vacuum, shedding light on the conditions required for sound to bridge the emptiness of space.
To achieve this astonishing feat, the researchers utilised piezoelectric materials, specifically zinc oxide crystals. Piezoelectric materials have a unique property: when subjected to force or heat, they generate an electrical charge. When sound waves interact with these crystals, they trigger vibrations that create electrical charges. This interaction within an electric field, shared between two closely spaced zinc oxide crystals, forms the basis of their groundbreaking experiment.
Here's how it works
When sound is applied to one of the crystals, it produces an electrical charge that disrupts the nearby electric field. Remarkably, if this crystal shares an electric field with another crystal, the disruption can traverse the vacuum between them. These disruptions mirror the frequency of the sound waves, effectively allowing the receiving crystal to reconstitute the sound on the other side of the vacuum.
However, there's a crucial limitation. This method is dependent on the wavelength of the sound wave. The disruptions cannot traverse a distance greater than the wavelength of a single sound wave. In theory, this principle applies to all sound frequencies, as long as the gap between the crystals is sufficiently small.
The researchers found that this phenomenon is not always consistent. In many experiments, sound transmission was imperfect, with parts of the wave being warped or reflected as it passed through the electric field. Nonetheless, there were instances where the piezoelectric crystals flawlessly transmitted the entire sound wave with 100% efficiency.
"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% efficiency, without any reflections," explained study co-author Ilari Maasilta, a material physicist at the University of Jyväskylä in Finland.
This discovery opens the door to exciting possibilities. While sound transmission through a vacuum may not be practical for everyday applications, it could revolutionize the development of microelectromechanical components (MEMS) used in technologies like smartphones. Moreover, it might find applications in controlling heat, which could have implications for various industries.