The phrase that became most emblematic in the world of science fiction related to space is the one that Ridley Scott made famous in Alien: “In space, no one can hear you scream.” And although it sounds terrifying imagining it, it’s most likely we will never need to cry for help out there. Even so, the question remains, why can’t we hear screams in space?
To get to the right answer, we must first understand that the planet serves as a shield for life in every sense. Just as marine life is immersed in its habitat that keeps it safe from the elements, we are also immersed in a fluid that we cannot see, but that exists. The atmosphere, like water, has its own density and is composed of molecules of different gases. So, in a certain way, we live inside a bubble that the composition of its interior (the atmosphere) makes possible everything that you already know and that now seems normal to you.
Fluid as a vehicle
But what does this have to do with screaming in space? It turns out that survival is not only about staying alive but also about developing behaviors and functionalities that are useful to us as a species. One of these functionalities is precisely sound. Not only do humans use it, but several species depend entirely on their sounds to communicate with each other. For example, fireflies depend on it to ensure their reproductive cycles and keep their species alive. On the other hand, cetaceans and bats have developed the ability to echolocate. Thus our world is not only a megadiverse in its life forms but also the soundscapes it offers us.
So, although it sounds obvious to us now because of habit, the truth is that sound is intrinsic to the Earth. Not because it does not exist in other regions of the cosmos, but because here it finds the perfect way to propagate. Sound is actually vibrations that are then interpreted by our brain depending on their frequency. These vibrations require fluids to propagate, and that is why the atmosphere, which contains millions of molecules very close to each other, is the perfect way for sound travel. With each sound we emit, we can move the molecules of the atmosphere closest to us; then these are charged and manage to move more molecules at the same time, triggering a chain reaction that ends with the propagation of sound.
So why can’t the screams be heard in space?
In space, on the other hand, the situation is very different. Out there, the scenario is more gloomy, and it is virtually empty and quiet. We say virtually because molecules do exist, but you can only find about 10 atoms per cubic meter. In the atmosphere, we have exponentially many millions more molecules per cubic meter. So if you emitted cries for help in space, no one could hear them for the simple reason that the sound would have no way to propagate and would die only after emitting it.
Text and photos courtesy of Ecoosfera
Translated by María Isabel Carrasco Cara Chards
