Lena Torres
The idea that sound cannot travel through a vacuum is a well-known concept, famously referenced in the film Alien with the tagline In space, no one can hear you scream. This is based on the fact that sound waves are created by travelling vibrations of particles in media such as air, water or metal. However, recent studies have suggested that sound may be able to jump between objects in a vacuum. This is because space is not a complete void; it contains interstellar gas and dust left behind by old stars, which has the potential to carry sound waves, albeit at an extremely low frequency that is beyond the range of human hearing.
| Characteristics | Values |
|---|---|
| Sound in a vacuum | Sound doesn't move through a vacuum as there are no molecules for the vibrations to move through |
| Sound in space | Space is not a complete vacuum and has gas and dust left behind by old stars that can carry sound waves, but at a very low frequency that is inaudible to humans |
| Sound waves | Sound waves can only travel through a medium if the length of the wave is longer than the average distance between the particles |
| Sound waves in space | Sound waves in space have a wavelength of 17 m and a frequency of 20 Hz, which is inaudible to humans |
| Sound waves below 20 Hz | Sounds below 20 Hz become infrasounds and are inaudible to humans |
| Sound of a black hole | The sound of a black hole is about 57 octaves below middle C, which is about a million billion times deeper than the lowest frequency sound humans can hear |
| Sound of an explosion in a vacuum | An explosion in a vacuum may be audible due to the lack of a high vacuum and the close proximity to the chamber walls |
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What You'll Learn
Sound waves require a medium to travel through
It is a well-known fact that sound cannot travel through a vacuum. This is because sound waves are travelling vibrations of particles in a medium such as air, water, or metal. In a vacuum, where there are no molecules, there is no medium for the sound waves to travel through.
However, this idea has been challenged by some recent findings. While it is true that sound cannot travel through a vacuum in the traditional sense, it has been discovered that under certain circumstances, sound can jump between objects in a vacuum. This is because space is not a complete and empty void; it contains interstellar gas and dust left behind by old stars, which provide a medium for sound waves to travel through.
The key factor determining whether sound waves can travel through a medium is the length of the wave relative to the average distance between particles in the medium. This is known as the ""mean free path". If the wavelength is longer than the mean free path, the sound waves can propagate through the medium. In the case of interstellar gas, the mean free path is larger than the wavelength of sounds with a frequency of 20 Hz, resulting in sound waves that are too low-frequency for humans to hear.
These low-frequency sound waves, known as infrasound, can be caused by events such as the explosion of a planet or spacecraft or the collapse of stellar bodies. While humans cannot hear these sounds, they can be detected and measured by specialized instruments. For example, NASA's Chandra X-ray space telescope observed ripples in the gas of the Perseus Cluster, which were determined to be caused by incredibly low-frequency sound waves generated by a rotating black hole.
Therefore, while it is true that sound waves require a medium to travel through, the nature of this medium can vary, and in certain cases, sound can propagate through a vacuum-like environment.
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Space is not a complete vacuum
It is often said that "in space, no one can hear you scream." This is because sound waves are travelling vibrations of particles in media such as air, water, or metal. Therefore, the assumption is that sound cannot travel through empty space, where there are no atoms or molecules to vibrate.
However, space is not a complete vacuum. While it is very close to being one, it is not entirely devoid of matter. In the Solar System, space contains an average of five atoms per cubic centimetre. Interstellar space, the space between stars, contains around one atom per cubic centimetre. Intergalactic space, between galaxies, contains about less than one atom in every cubic meter, which is 100 times fewer atoms than interstellar space.
The interstellar gas and dust left behind by old stars and sometimes used to create new ones can carry sound waves, but these waves are of such low frequency that they are beyond the capabilities of human hearing. The particles are so spread out that the resulting sound waves are too low in frequency for humans to hear. For example, the sound of a black hole is about 57 octaves below middle C, which is well below the range of human hearing.
Additionally, for a perfect vacuum to occur, space would need to be entirely devoid of energy fluctuations, which is not possible due to quantum theory. These energy fluctuations, known as 'virtual particles,' constantly appear and disappear, even in seemingly empty space. Therefore, while space is very close to being a vacuum, it is not a complete one due to the presence of some atoms and energy fluctuations.
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Sound can travel through interstellar gas and dust
It is a well-known fact that sound cannot travel through a vacuum. This is because sound waves are travelling vibrations of particles in a medium such as air, water, or metal. Therefore, they cannot travel through empty space, where there are no atoms or molecules to vibrate. However, recent discoveries have challenged this notion, suggesting that under certain conditions, sound may be able to propagate in a vacuum.
This leads us to the concept of interstellar space, which is not entirely devoid of matter. The space between stars, known as the interstellar medium, contains gas, dust, and other materials left behind by old stars or used in the formation of new ones. This interstellar medium can carry sound waves, but the resulting sound waves are of an extremely low frequency that is beyond the range of human hearing.
The interstellar medium includes interstellar dust clouds, composed of atoms and molecules, along with larger dust granules that contribute to the overall mass. These dust clouds interact with stellar winds, which are outflows of hot gas from the galactic nucleus, leading to instabilities that generate sound waves. Additionally, the interstellar medium can be influenced by galactic waves or spiral density waves, which are large-scale pressure fluctuations caused by the motion of stars and galactic winds in a spiral galaxy.
The speed of sound in interstellar space can vary depending on the density of the medium. For example, in a typical nebula, the speed of sound can reach about 10 kilometers per second, much faster than the speed of sound in Earth's atmosphere. Furthermore, the explosion of a star can generate shock waves similar to a sonic boom, creating the intricate patterns often observed in a supernova's expanding cloud of debris.
While sound waves can exist in the interstellar medium, they are not audible to humans due to the vast distances between particles and the resulting low-frequency sound waves. However, these sound waves can provide valuable information about the processes occurring in interstellar space, contributing to our understanding of the universe.
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Sound waves with long wavelengths can travel through space
It is a well-known fact that sound cannot travel through a vacuum, as there are no molecules for the sound vibrations to move through. However, this is only true to an extent. While space is almost a vacuum, it is not a perfect one. Interstellar gas and dust left behind by old stars can carry sound waves, but the particles are so spread out that the resulting sound waves are of an extremely low frequency, which is beyond the range of human hearing.
Sound waves are created by particles of matter interacting with other particles of matter. In the case of sound in the air, this is achieved through molecules bumping into each other. For sound to travel through space, it needs to have very long wavelengths, which means very low frequencies. The sound of the sun, for example, has wavelengths of hundreds of thousands of kilometres, but at frequencies so low that only a planet-sized ear drum could pick them up.
Sound waves with long wavelengths can, therefore, travel through space, but not in a way that is audible to humans. These sounds have to be of a low pitch, with wavelengths longer than the distance between particles, in order to make it from one particle to the next. Sounds with frequencies below 20 Hz become infrasounds, which are inaudible to humans.
On Earth, the sounds of very strong earthquakes can sometimes be intense enough to pass through the atmosphere and into space as infrasound. Additionally, for a short period after the Big Bang, the universe was dense enough for normal sounds to pass through it.
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Human ears cannot hear very low-frequency sounds
The commonly stated range of human hearing is between 20 and 20,000 Hz, although there is considerable variation between individuals, especially at higher frequencies. This range is not absolute and is only a general limit. Many adults can only register sounds up to 15 to 17 kHz, and this upper limit decreases with age.
Sounds with frequencies below 200 Hz tend to be either inaudible or barely audible to humans. For example, a wind turbine, a roaring crowd at a football game, or a jet engine running at full throttle produce sound waves well below the frequencies humans can hear. However, just because these low-frequency components are inaudible does not mean they have no effect on our ears. Exposure to low-frequency sounds can alter the functioning of the inner ear, even changing the way it works for minutes after the noise ends.
In a study conducted by neurobiologist Markus Drexl at Ludwig Maximilian University in Munich, Germany, 21 volunteers with normal hearing were exposed to a 30-Hz sound for 90 seconds. This deep, vibrating noise is comparable to what one might hear when driving fast down a highway with the windows open. After the noise ended, the participants' ears exhibited fluctuations in spontaneous otoacoustic emissions (SOAEs) for about three minutes. SOAEs are faint whistling sounds naturally emitted by a healthy human ear. While these changes are not indicative of hearing loss, they suggest that the ear may be temporarily more susceptible to damage after exposure to low-frequency sounds.
Extended exposure to low-frequency sounds can lead to permanent, irreparable damage to our ears. Therefore, it is essential to be mindful of our hearing capabilities and take precautions when exposed to such sounds.
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Frequently asked questions
No, sound does not exist in a vacuum because there are no molecules for the sound vibrations to move through.
In a vacuum chamber, it is possible that there is a leak that keeps you from obtaining a good vacuum. The lack of a high vacuum could be helping the sounds travel. It is also possible that what you are hearing is not traditional sound waves but rather the expanding gas from the explosion.
Space is not a complete vacuum. It is filled with interstellar gas and dust left behind by old stars. These clouds of gas are sometimes dense enough to carry sound waves, just not sounds that are perceptible to humans.
