Sound waves cannot travel in the vacuum of space, illustration by NASA.
“In space, no one can hear you scream.” This chilling tagline from the movie Alien has ingrained the idea of a silent cosmos in popular culture. But is it just a cinematic scare, or is there truth to the silence of space? Jasmine, a 14-year-old from Everson, Washington, asked a question that gets to the heart of this cosmic concept: “How far can sound travel through space, since it’s so empty? Is there an echo in space?” The straightforward answer is yes, space is largely silent. Let’s delve into why.
The Science of Sound: How Sound Waves Work
To understand why space is mostly devoid of sound, we first need to explore how sound itself functions. Sound is essentially a wave of energy. This energy propagates through a medium – it could be a solid, a liquid, or a gas. Think of sound as a compression wave, also known as a longitudinal wave. When you speak, your vocal cords vibrate, creating energy that compresses the air in your throat. This compression then travels outward as a sound wave.
A helpful analogy to visualize this is a Slinky toy. Imagine stretching out a Slinky and giving one end a sharp push. You’ll see a compression wave travel down the Slinky’s coils. Similarly, when your vocal cords vibrate, they disturb the air molecules around them. These molecules bump into their neighbors, which in turn bump into their neighbors, and so on, carrying the sound energy outward from your mouth.
Sound waves travel remarkably fast through air, reaching speeds of around 760 miles per hour (1,223 kilometers per hour). That’s faster than a commercial airplane!
The Vacuum of Space: Why Silence Reigns
So, what happens to sound in space? The critical difference is that space is a vacuum. This term, derived from the Latin word for “empty,” means that space contains extremely little matter. In fact, space is so empty that it’s practically devoid of atoms and molecules in vast stretches.
Sound waves require atoms and molecules to act as carriers. They need these particles to bump into each other and transmit the compression wave. In the near-absence of matter in space, there’s simply nothing to carry sound. It’s not that something is blocking sound in space; rather, there’s no medium for it to travel through in the first place. This absence of a medium also explains why there are no echoes in space. An echo is created when sound waves bounce off a hard surface and return. Without a medium to transmit the initial sound wave, there can be no echo.
Interestingly, the silence of space becomes a secondary concern if you were exposed to the vacuum without a spacesuit. The rapid expansion of air in your lungs due to the pressure difference would cause them to rupture. Within a mere 10 to 15 seconds, oxygen deprivation would lead to unconsciousness – a far more immediate threat than the inability to be heard.
Sound in Our Solar System: Hypothetical Scenarios
While true sound as we know it doesn’t travel through the vacuum of space, scientists have explored how our voices might sound on other planets within our solar system, specifically Venus and Mars. These are hypothetical scenarios, as Mars has a frigid environment and a thin atmosphere composed mainly of unbreathable carbon dioxide. Venus is even more extreme, with scorching temperatures and a dense carbon dioxide atmosphere.
On Mars, if you could somehow speak, your voice would likely sound tinny and high-pitched, somewhat like a piccolo. Conversely, on Venus, your voice would be much deeper, resonating like a bass guitar. This difference is due to the density of the atmosphere. The thin atmosphere on Mars results in higher-pitched sounds, while the dense atmosphere of Venus produces lower-pitched sounds. Scientists have even simulated other sounds in our solar system, such as what a waterfall might sound like on Saturn’s moon Titan, taking into account the atmospheric conditions on these celestial bodies.
The Sounds of Deep Space: Beyond the Vacuum
While space is a very effective vacuum when considering everyday sound, it’s not a perfect vacuum. Interstellar space does contain a sparse amount of particles, primarily hydrogen atoms. Beyond Earth’s atmosphere, you might find about five particles per cubic centimeter – roughly the size of a sugar cube. Compare this to the air we breathe, which is 10 billion billion (1019) times denser! The particle density decreases further as you move away from the Sun, and in the space between stars, it drops to approximately 0.1 particles per cubic centimeter. In the vast voids between galaxies, it’s even lower, becoming fantastically empty.
However, these voids aren’t entirely silent in a different way. The extremely sparse matter in these regions exists in a state called plasma, superheated by radiation from stars. Plasma is a state of matter where electrons are stripped from atoms, creating a gas of ions and electrons. In plasma, the physics of wave propagation becomes more complex. Waves can travel much faster in this low-density medium, and they possess significantly longer wavelengths.
In a fascinating example, NASA released a recording in 2022 that represents “sound” from space, specifically from the Perseus galaxy cluster, 250 million light-years away. Using X-ray data, they created an audible representation of how a supermassive black hole agitates the surrounding plasma. While the black hole itself doesn’t emit sound in the conventional sense, the diffuse plasma around it carries very long wavelength sound waves.
This “sound” is naturally at an incredibly low frequency, 57 octaves below middle C, far below human hearing range. By raising the frequency to audible levels, NASA created a chilling sound that has been described as the “growl” of a black hole in deep space. This isn’t sound traveling through space in the way we typically understand it, but rather a translation of plasma waves into audible frequencies, offering a unique glimpse into the dynamics of the cosmos.
In conclusion, while the common phrase “in space, no one can hear you scream” holds true for the vacuum of space and traditional sound waves, the universe is far from silent. In the vastness of deep space, particularly within plasmas, forms of wave energy exist and can be translated into what we perceive as sound, revealing the universe in a symphony far beyond our everyday auditory experience.
This article is adapted from an article originally published on The Conversation.
