How Does Sound Travel in Vacuum (2025) The Breakthrough Discovery

Written By: Arnav Gill
Updated On: November 6th, 2025

Every space movie fan knows the famous tagline from Alien: “In space, no one can hear you scream.” This scientific fact has been taught in physics classrooms for generations – sound cannot travel through a vacuum because it needs a medium to propagate. But in 2025, physicists discovered something remarkable that challenges this fundamental understanding.

How does sound travel in vacuum? Traditionally, it doesn’t – sound waves require particles to vibrate and transfer energy. However, recent research has shown that under specific conditions using piezoelectric materials, sound can effectively “tunnel” across small vacuum gaps through energy conversion.

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This breakthrough doesn’t overturn basic physics but reveals a fascinating exception to the rule. I’ve followed this research closely since it was published in Communications Physics, and the implications are both scientifically significant and practically useful.

In this guide, I’ll explain both the traditional understanding and the new discovery, using clear examples and addressing common questions about sound propagation in empty space.

Understanding Sound as a Mechanical Wave

Sound is a mechanical wave that propagates through the vibration of particles in a medium. Unlike electromagnetic waves like light, sound cannot travel through empty space because it needs physical matter to transmit its energy.

When you speak, your vocal cords create pressure variations in the air. These compressions and rarefactions cause air molecules to vibrate, passing energy from one molecule to the next like a line of falling dominoes. Each molecule only moves slightly, but the wave pattern travels outward at about 343 meters per second (at room temperature).

This mechanical nature is why sound behaves differently in various media:

Air: Sound travels at 343 m/s due to the spacing between gas molecules
Water: Faster at 1,480 m/s because liquid molecules are closer together
Steel: Much faster at 5,960 m/s as solid particles are tightly packed

The density and elasticity of the medium determine how quickly sound can propagate. Without any particles to vibrate, as in a vacuum, sound has no way to travel.

Why Traditional Physics Says Sound Can’t Travel in Vacuum?

A vacuum is, by definition, a space devoid of matter. Even the “perfect vacuum” of space contains a few particles per cubic meter, but not enough to sustain sound wave propagation.

Think of sound like a crowd wave at a sports stadium. The wave moves because people stand up and sit down in sequence, passing the motion through the crowd. If there were no people in the stadium, the wave couldn’t travel – there’s nothing to carry the motion.

This is why space is silent. When stars explode or spacecraft move, they don’t produce sound that could travel through the vacuum between celestial bodies. The sound effects in space movies are artistic liberties taken for entertainment.

Physicists have confirmed this through countless experiments. The classic demonstration involves a ringing bell inside a vacuum chamber. As air is removed, the sound gradually fades until it’s completely silent, despite the bell still visibly vibrating.

⚠️ Important: Even in space, astronauts can hear inside their spacecraft because there’s air inside, and sound can travel through their helmets and suits when in physical contact.

The 2023 Breakthrough: How Sound Can Travel in Vacuum?

In August 2025, researchers at the University of Jyväskylä in Finland published groundbreaking research showing that sound can, under specific conditions, travel across a vacuum gap. Led by physicists Ilari Maasilta and Zhuoran Geng, the team demonstrated a phenomenon called “acoustic tunneling.”

The key to this discovery lies in piezoelectric materials – crystals that convert mechanical energy into electrical energy and vice versa. When paired across a tiny vacuum gap, these materials create a bridge for sound to cross where none should exist.

Here’s how it works:

First crystal: Sound waves cause the piezoelectric crystal to vibrate mechanically
Energy conversion: The mechanical vibrations generate an electric field
Vacuum crossing: The electric field jumps across the vacuum gap
Second crystal: The electric field causes the second crystal to vibrate
Sound reproduction: The second crystal’s vibrations recreate the original sound wave

The team used zinc oxide crystals in their experiment, successfully transmitting sound across a vacuum gap. While the distance was microscopic (nanometers to micrometers), this proof of concept changes our understanding of what’s possible.

How Acoustic Tunneling Works?

Acoustic tunneling exploits a quantum mechanical principle where particles can pass through barriers they shouldn’t be able to cross. While not exactly quantum tunneling, the acoustic version shares similarities – sound waves effectively “tunnel” through an impossible barrier.

The process requires specific conditions:

Piezoelectric materials: Both sides of the vacuum gap must have crystals that convert between mechanical and electrical energy
Matching frequencies: The crystals must resonate at compatible frequencies
Small gaps: Current technology limits this to microscopic distances
Specific wavelengths: The sound waves must have appropriate wavelengths for the crystal properties

The researchers found they could transmit both audible sound and ultrasound frequencies, with efficiency depending on the exact setup. This isn’t sound traveling through the vacuum in the traditional sense – it’s sound being converted to electricity, crossing the vacuum as an electric field, then being converted back to sound.

Piezoelectric Effect: The ability of certain materials to generate an electric charge in response to applied mechanical stress, and conversely, to deform when an electric field is applied.

Practical Applications and Future Implications

This discovery isn’t just academically interesting – it has practical applications in technology we use every day. Micro-electromechanical systems (MEMS) found in smartphones and other devices could benefit from this phenomenon.

Potential applications include:

Heat control systems: Using acoustic tunneling to manage thermal energy in microelectronics
Sensor technology: Creating sensors that can detect and transmit sound across vacuum barriers
Quantum information science: Using sound waves as carriers for quantum information
Advanced manufacturing: New methods for precision engineering at microscopic scales

The distance limitation remains a challenge – current technology only works across microscopic gaps. However, as research continues, we may see new materials and techniques that extend this capability to larger distances.

Frequently Asked Questions

Is space really completely silent?

Space is not a perfect vacuum – it contains a few particles per cubic meter. However, this particle density is far too low for sound waves to propagate effectively. For practical purposes, space is silent to human hearing.

How do astronauts communicate in space if sound can’t travel?

Astronauts use radio waves to communicate, which are electromagnetic waves that don’t need a medium. Inside spacecraft or suits, they can speak normally because there’s air to carry the sound.

Can we create a perfect vacuum on Earth?

Even the best vacuum chambers on Earth can’t achieve a perfect vacuum. The best laboratory vacuums still contain millions of particles per cubic meter, though this is sparse enough for sound to be effectively blocked.

Why do movies have sound in space scenes?

Space movies include sound effects for artistic and dramatic reasons. Most viewers expect sound during action scenes, and complete silence would feel unnatural to audiences, even if scientifically accurate.

Could this discovery change how we understand the Big Bang?

The Big Bang wasn’t silent because the early universe wasn’t a vacuum – it was incredibly dense with particles and energy. Sound waves did propagate in the early universe, leaving imprints we can detect today.

Final Thoughts

The discovery of acoustic tunneling doesn’t overturn our fundamental understanding of sound – it adds a fascinating exception to the rule. Sound still can’t travel through a vacuum in the traditional sense, but clever physics allows us to bridge that gap using energy conversion.

As research continues, we may find new applications for this phenomenon that impact everyday technology. For now, it stands as a beautiful example of how scientific discoveries can reveal unexpected possibilities even in well-understood areas of physics.

The universe remains mostly silent, but through clever application of physical principles, we’re finding ways to make sound travel where it shouldn’t – at least across tiny gaps.