[su_label type=”info”]This question was submitted by Tammy[/su_label]
For any sounds to reach your ear, it would need a medium (fluid, solid) to propagate. For example, when your friend calls out your name, her vocal folds vibrate and make the sound of your name ‘Tammy’. This vibration traverses through the air, into your ear by vibrating all the air molecules in between you and your friend. When it reaches your ear, the mechanical vibrations in your middle ear is sensed by your hair cells in your cochlea, which in turn sends signals to your brain and helps it to interpret the sound.
The space is almost a vacuum, as all the matters in the universe are separated by a very huge distance. So the distribution of air molecules is of insignificant amount–the density is negligible. When your friend calls you out in the space (hypothetically assuming that you are superheroes who can survive vacuum), there won’t be any air molecules to help traverse her voice–the vibration–to reach your ears. This is the reason why you can’t hear sound in space.
But you can talk to each other if you have a space suit and the right equipment in space to convert the sound into an electromagnetic wave and vice versa. That equipment is called as a radio :) Unlike the mechanical sound waves, the electromagnetic waves can travel through vacuum. So if your friend calls your name in her radio, then her voice will be converted into electromagnetic waves and then it will travel through the vacuum to be received by your radio to be converted into sound again.
If sound needs a medium to travel, shouldn’t it be the same case for electromagnetic waves? How does it travel without a medium?
It doesn’t make sense right? :) This exact conundrum bothered many physicists in the past. Many believed that there was indeed a medium called the luminiferous aether. Then came Michelson and Morley, who conducted the Michelson–Morley experiment to prove that the said medium did not exist at all.
Albert Einstein later proved this, when he came up with Special Relativity. Electromagnetic waves are more of a self-propagating wave, where the medium is its own electromagnetic field. This electromagnetic field is everywhere, and radio waves, light waves, all are disturbances of this field.
As this electromagnetic field is everywhere, the electromagnetic waves can traverse anywhere—even in the vacuum. In the case of sound waves, they are truly a mechanical wave. They cannot exist without a medium like air, solid, or liquid.
So the electromagnetic field is the medium for the electromagnetic waves! But how does this differ from the aether?
In general, yes! They both seem to refer the same notion. But the key difference here is that the aether was assumed to be a fixed frame of reference and light traversed through it mechanically—like sound waves through air. But in reality, it’s not the case. There is no true fixed frame of reference—this is what Einstein stated in his Special Relativity. Everything is in relative motion to each other. And electromagnetic waves are simply a disturbance in its own field, unlike aether—which people in the past assumed it as a medium, much like the water, with its own properties that carried the wave.
Thank you for explaining this in detail!
You’re welcome! :)