Sound has fascinated humankind for time immemorial. There are numerous examples of ancient cultures around the globe who have postulated that we are born of sound. Whole cosmologies have been built upon this notion. How is it that sound can move and inspire us to such a degree?
To me personally, sound has always felt like something so primal and natural, as something that puts me in contact with the mystery of what is to be alive. Whilst we can and will (try at least) to explain what sound is and how it moves through space, what we can’t explain so easily is how it is capable of moving us to such a degree.
That is to say, we can so readily explain the subjective experience of sound and how it’s able to instill such intense emotions in us.
Whilst I do have my views on this, let’s save that for another time and look at how sound travels through time and space. But before we can answer this question we should first look at what exactly sound is.
So What Exactly Is Sound?
Just like heat and light, a sound is a form of energy.
Sound is the product of vibrations of one or more objects. These vibrations have to travel through a medium, which for us humans usually tends to be the air. So the sound is the product of vibrating bodies. When the vibrating bodies stop, so does the sound.
We can easily perceive this in action if we touch a bell after it’s been stricken. We can feel the vibrations that produce the sound of the ringing bell simply by placing our hands on the bell. Once the vibrations stop so will the sound.
Sound is a pressure wave created by these vibrating bodies. these vibrations set the particles in the adjacent medium (most often air for us) into vibrational motion. Whenever a human speaks, then the diaphragm in his throat vibrates causing sound.
The stronger the vibrations are, the louder the sound is to us as it reverberates through our eardrums. How loud a sound is depends on how far a vibrating object is from the listener. Human ears are capable of perceiving frequencies between 20 and 20,000 hertz.
Pitch is the quality of the sound itself and itself depends on the speed of the vibrations. Different pitches of sound are produced by different materials as they vibrate. A material that vibrates quickly produces a high-pitch sound, whereas a material that vibrates slowly produces a low-pitched sound.
Sound waves need a medium to travel through and cannot travel in a vacuum.
A study on sound should begin with a look at the properties of sound waves. There are two types of sound waves that exist, with the difference being in how they are propagated. These two types are known as transverse waves and longitudinal waves.
An example of a transverse wave is one in which a string is stretched between two points, with one end being wiggled back and forth, somewhat as you’d find on a guitar. In this example, the motion that constitutes the wave is perpendicular (or transverse) to the direction in which the wave is moving across the string.
Other examples of transverse waves are those generated by electromagnetic sources, such as radios and light. Here, the electric and magnetic fields constituting the wave oscillate in the direction perpendicular to the direction of propagation.
A longitudinal wave constitutes a wave that flows the same way as that of the propagation of the wave. You can create a longitudinal wave yourself by taking a coiled spring and compressing it, and then allowing the compression to release along the length of the spring.
We can view air as layers analogous to such coils. A sound wave, then, can be seen propagating as layers of push and pull against one another, in the same way that compression moves up and down the spring. A sound wave, thus, can be seen as alternate waves of high and low pressure otherwise known as compressions.
Put another way, sound waves can be viewed as periodic oscillating or vibrating around an equilibrium point in time and space.
Okay, But How Does Sound Travel?
One thing is having a rudimentary understanding of how sound is created, but it’s another thing entirely to understand just how it travels from one place to another. Now that we have touched upon how sound is made, we can look at how it moves through space. As has already been mentioned, the movement of sound waves is dependent on the medium through which it is moving.
As humans are terrestrial beings, the medium through which sound moves relative to ourselves is usually air. However, it’s worth remembering that sound waves will behave somewhat differently in other mediums, such as in water for example. For now, though let us concentrate on how sound travels through the air.
Sound can be viewed as a disturbance in mechanical waves. This disturbance transports energy via a medium. The disturbance is a vibrating object. This vibrational energy carries on in a chain reaction until all the energy has all been expended. The medium through which this energy travels can be any set of particles, such as gases liquids, and solids.
So, as a sound wave passes through the air, there is a series of molecular collisions that happen. It’s important to remember that it is not the air particles themselves that are traveling, but rather they’re disturbed from their resting point to which they will eventually return as the energy runs out.
The speed of the waves depends on the medium through which the sound waves are traveling. When traveling through the air, the speed is about 330metres per second. As many people are aware, sound is incapable of traveling through a vacuum as there are no particles to carry the vibration through space.
What About Water Or Other Mediums?
Air is made up of many tiny particles. These particles crash and collide with one another when a vibration occurs, causing the vibration to pass from one particle to another. This vibration then passes through the air and into a person’s ear. This causes the eardrum to vibrate, allowing us to perceive this vibration as a sound.
Sound isn’t just restricted to moving through the air. As a simple experiment, place your ear on the nearest table. Then take your finger and tap the table. Your finger colliding with the table creates the initial disturbance of the surrounding particles by sending vibrations through the table.
What you end up hearing are the particles in the table colliding with one another, thus becoming the medium for the sound. Or more specifically, the air particles in the table are colliding with air particles between the table and your eardrum.
We refer to this movement of a wave from one medium to another as transmission.
The air particles collide with your ear’s tympanic membrane, which is more commonly referred to as your eardrum. This is the beginning of a series of further vibrations inside several structures in the ear which is interpreted by the brain as sound.
The properties of a sound wave are changed when it travels through different media, such as a solid, liquid, or gas. The denser the medium sound has to travel through, the faster it travels. For example, sound travels faster through water than it does through air, as water is denser than air.
It travel faster still through a solid mass than through water. Sound will also travel at a different (although largely imperceptible) speed on a hot day as opposed to a cold day.
Can Sound Travel In Space?
‘Space,’ for our discussion, can be defined as the region in the wider universe outside of the earth’s atmosphere. Most people are already aware that ‘space,’ is a vacuum. A true vacuum means an area devoid of matter. You may be wondering how things thing we call ‘space,’ which contains all known things in existence including stars, comets, planets, and so forth can be devoid of matter.
The simple answer is that between these giant cosmic bodies there are unfathomable amounts of empty space, sometimes referred to as interstellar space. Interstellar space is practically devoid of matter, so by the same token, it’s practically a vacuum.
As we mentioned, sound needs a medium to travel, and interstellar space, being almost entirely devoid of matter means sound cannot travel. The massive distances between particles in interstellar space are so great that they would rarely collide.
However, there are some ways that a human could hear in outer space. Radio waves are capable of traveling in space, so if you were wearing a spacesuit containing a radio, you could technically hear sound. This is because radio waves are electromagnetic waves and not mechanical waves. Electromagnetic waves are capable of transmitting energy through a vacuum.
Also if you were to find yourself in outer space and were to bump your helmet against a hard surface, you would be able to hear a sound. This is because the sound waves would have a physical medium to travel through; the helmet and the air inside of the helmet. However, as you’d still be surrounded by ’empty space,’ an outside observer wouldn’t be able to hear anything.
Digging A Little Deeper
If we want to dig a little bit deeper, then we can say that the statement the ‘sound can’t travel through space,’ isn’t completely true. As it turns out space isn’t completely and entirely void of matter, although huge amounts of it are.
There are dust and gas particles leftover from expired stars that, over millions of years may collide and form new planets. These particles do have the potential to carry sound waves, we just don’t have the faculties to listen to them.
Our inability to hear these waves is because the particles are so spread out and the frequencies are so low that they are rendered inaudible to the human ear. As we’ve already mentioned, sound travels through the dispersion of waves, much like ripples in a pond spread out after you drop a stone into it.
As the ripples get further and further away the sound gradually loses its force. this is why we can only hear sounds that are generated close to us.
As a sound wave moves, it causes oscillation in the air pressure around it. The time between these oscillations represents the frequency of the sound, which we measure in Hertz. the distance between the oscillating peaks is the wavelength.
If the area between the air particles is greater than this wavelength, then the sound is unable to surpass the gap and the ripple dies. Therefore sounds have to have a very wide wavelength to reach from one particle to the next. Due to the vast distances involved, they would appear as a very low sound that would be inaudible to human ears.
Once sound drops below 20 Hz, they become infrasound which is beyond our capacity as humans to hear.
The lowest note measured by humankind thus far is that emanating from a black hole, which is reportedly 57 octaves below middle C. This makes this sound a staggering million billion times deeper than a sound we are capable of hearing.
You’d expect to be able to measure one oscillation of a black hole sound wave once every 10 million years. Our human ears, on the other hand, fall short and stop hearing sounds that oscillate at 20 times per second.
To Sum Up.
A sound is a form of energy that is the product of one or more objects vibrating. These vibrations have to travel through a medium, which most of the time is air for us humans. Sound vibrations will behave differently if traveling through liquids or gases.
Sound is a pressure wave created by the vibrating bodies of a given particle. These particles cause particles in the adjacent medium into a corresponding vibrational momentum. This momentum, if we are close enough, will cause our eardrum to vibrate as well, which our brain will register as sound.