Shh! Space's Silence
- STEAMworks OC
- Aug 30, 2020
- 5 min read
There is a popular saying that screams are silent in space, but does this suggest that there is a complete absence of sound, or just a silence that only humans experience? The answer might be closer than people think if they take the time to listen to it.
Throughout history, silence has often proven to be more meaningful than words. True power comes from conveying a powerful message without having to say anything. What is interesting to consider is how the most popular statement of all time comes from the infinitely large expanse presented to everyone on a daily basis: outer space.
How does sound travel?
Sound travels through vibrations (back and forth motion of the particles in an elastic body or medium) that follow wave patterns, which is what influences the name sound waves. These sound waves create vibrations in molecules, such as air or water, that then carry it along to other molecules. Sound is very reliant on these vibrations in order for it to travel, ensuring that molecules continue to bump each other as the chain continues. Unlike how light travels, sound always needs a medium, which is essentially the thing by which or through an action is done. The use of mechanical waves is what requires the medium to transfer their energy from one location to another. There are no particles involved, only the waves. Because sound’s energy disappears quickly, it does not travel far. This is why sound is not continuous; as the energy continues and more molecules vibrate, they begin to stiffen their movement until they eventually stop moving completely.
Sound can be measured in various ways. One way is through frequency, which is the number of times per second that a sound wave repeats itself. Frequency is also known as pitch because it determines the note, like the different notes on a piano. The more sound waves that pass through a certain point in a second, the higher the frequency, which leads to a higher pitch. The unit for frequency is hertz (Hz). The highest note on a piano, C8, is 4,186 Hz while the lowest note, A0, is 27.5 Hz. The second way that sound is measured is in decibels (dB), which counts the power or degree of loudness by comparing it to its decibel scale. The higher the number of decibels, the louder a sound is. For example, a whisper is 30 dB while a rock concert can be up to 140 dB.
Leo Beranek, an American acoustics expert, used his knowledge of how sound travels to design a chamber that absorbs reflecting sound waves. Thus, he created an anechoic chamber, meaning it has a complete lack of noise free from echo. Located in Orfield Laboratories in Minnesota, the chamber is famous for being the quietest place on Earth. Humans have an average hearing range of 0 to 140 dB. The world record held for Minnesota’s anechoic chamber is sound waves reflected at -20 dB. This does not mean that decibels under 0 have no sound, but simply that humans are not equipped to hear them. Dogs prove this to be true since they can hear sounds at frequencies humans cannot, which is how dog whistles were created. Through blowing whistles that have a frequency of up to 12,000 Hz, dogs are able to hear sounds as low as -15 dB.
While these chambers are not open to the public, individuals who have tried to sit in the room have not lasted long. Through being challenged to sit in the dark with only the sounds of their own heartbeat or lungs to occupy their ears, the natural tendencies humans crave kick in. NASA has sent astronauts in training down to the anechoic chamber to prepare them for space’s silence. The record for the longest that a person has sat in the anechoic chamber is 45 minutes!
How is space silent?
The lack of sound in space is due to the fact that space is a vacuum. This means that the parts of space farthest away from large celestial bodies have much lower concentrations of particles compared to other atmospheres (the gases surrounding a planet). This immense lack of matter is what prevents conventional methods of sound travel to occur. As previously mentioned, sound moves through mediums in the form of mechanical waves, which vibrate molecules to carry energy. However, as space is missing a substantial amount of molecules for these waves to pass through, sound can no longer travel. This includes echoes as well, which require an object to reflect off of.
This vacuum also accounts for why humans are unable to breathe in space. If an astronaut were to take off their helmet, the vacuum would immediately pull air from their body, depriving their lungs of oxygen. Without this necessary air in the lungs, their blood would stop sending oxygen to the brain. When this occurs, they would quickly lose consciousness and later die. The large difference between Earth’s atmosphere and space is obvious from the 15 seconds that it takes for this process to take place.
What other factors affect sound speed?
A common misunderstanding is that air pressure has a large effect on the speed of sound. While sound travels faster at lower altitudes like sea level, the main factor for its speed is the temperature. In environments with higher temperatures, molecules collide with one another quicker. This has a positive effect on sound waves as they pass through.
Water differs greatly from air when it comes to sound mediums. Sound is able to travel five times faster in water thanks to its density. Water molecules are packed tightly together, allowing the energy that the sound waves carry to transport quicker. In gases, it is an increase in temperature that causes the molecules to move faster instead of its density. Despite how denser cooler temperatures are, air molecules accelerate sound waves in warmer environments. Due to the lack of air in space, there is little to no air pressure. Space has an air pressure of 4.3 pounds per square inch while Earth has an air pressure of 14.7 pounds per square inch. If water were to be poured into space, it would immediately vaporize or boil away. As the air pressure drops, the temperatures needed to boil water also drops. Therefore, no liquid water is present in space to have sound travel through. Molecules are too far apart to transmit sound.
So does space really have no sound?
The easy response to this question is no, space is not truly void of any sound. In “corners” of the universe where clusters of gas and dust from dead stars remain, are particles present and dense enough to create sound. An example of sound in space is black holes, as recorded in 2003 at NASA’s Chandra X-ray Observatory over 250 million light years away. However, this sound was billions of decibels lower than what humans are capable of hearing. So while there is evidence of sound in unique areas of the universe, the saying that “in space, no one can hear you scream” holds to its truth. With another mystery of the universe solved, consider looking up to the sky the next that a need to yell occurs; the solution is only 62 miles up.
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