If sound waves travel by pushing particles back and forth, then how exactly do electromagnetic/radio waves travel through the vacuum of space and dense matter? Are they emitting… stuff? Or is there some… stuff even in the empty space that they push?
In: Physics
EM waves “propagate” (travel) as a disturbance in the electromagnetic field, which does not require “stuff” (a medium) to exist. Photons are the particle representation of an EM wave, and can help us to better understand how energy can travel through a vacuum without any “stuff”
The electromagnetic field exists everywhere there is space.. there is no “stuff” in the way we would usually understand it like when we think of sound waves. It is just the potential energy content of space itself (essentially zero in a vacuum, setting aside other inputs and other kinds of fields and exotic quantum effects)
Think of it this way: Space can contain nothing (absolute vacuum), or it can contain something like mass (things like stars, plants, dust, gas, atoms etc), or energy (things like electromagnetic energy, gravitational energy etc). There is no “medium” other than empty space itself – things either exist in a bit of space, or they don’t
When you create electromagnetic energy, it has to go somewhere… The spacetime location where you created it (vacuum or not) now contains it.
If it’s not absorbed by something (like a planet or a speck of dust or molecule of gas), we can model this as a mass-less particle that contains that energy. Or a wave in the EM field that carries the energy, depending on how you look at it.
Put another way, if there was nothing in that bit of space before, you would model the mass and energy content of that space as zero, or the state of the EM field within it as “zero”. But now that you put something in this space, it now contains a specific thing with energy greater than zero, with direction and speed (a photon), OR a value in the EM field greater than zero, that travels through propagation (ie transferring the energy of one piece of space to the piece of space next to it)
**TL;DR: EM waves/Photons don’t require anything to exist previously in the space it travels through, only the ability for space to contain a bit of energy at all**
Sound Waves are pressure waves.
Radio waves are made of light.
Thats the simplest answer, I think you might not have had that understanding when asking your question.
There are other, way more detailed answers here if you want to go deeper than that
Actual ELI5 answer:
Electricity generates magnetism in front of it and magnetism generates electricity in front of it. Hence, this loop of exchange between electricity and magnetism moves forward without the need for any other medium.
Bonus ELI5:
The speed of light isn’t the speed of anything in particular about this phenomenon, it’s just the speed of “causality”, eg the speed at which cause and effect happen in the universe. This is why it’s a fundamental limit of the universe.
You know that globe we put on your desk so you wouldn’t fail geography? It’s a great model of the earth, isn’t it. But the fact that it’s a great model doesn’t mean the earth is made of polypropylene and made in China.
Waves and particles are good *models* of light and are really really useful at predicting the behaviour of light.
But what *is* light?
Light is a charged particle over *here*, usually an electron, moving in a way that it loses energy. And then after a time delay, another charged particle, again usually an electron over *there* gains energy and moves in response.
That’s it. That’s all that *actually* exists.
Waves and particles are just models. They are useful for predicting what electron over *there* will wiggle, how it’ll wiggle, and when it will wiggle in response to the electron over *here*. But that’s it. Don’t get caught up in ascribing aspects like physicality to photons. You cannot *have* a jar of photons. They don’t really *exist* like that.
Similarly, some behaviour of *sound* – which is most definitely a wave with a real physical presence – has some behaviours in semiconductors that are particle like. So a particle called a ‘phonon’ was described as a ‘particle of sound’ that is great for predicting the behaviour. But you can’t have a jar of phonons any more than you can have a jar of photons.
So try not to get too hung up on it. Electron A wiggles. Electron B wiggles. Energy is transferred from A to B. The rest is just polypropylene and made in China.
I don’t feel like these are ELI5 enough. Heres my attempt:
You are right that sound is a ripple in the air just like when you make ripples in water. Light is also a ripple but in something called the electromagnetic field. It is special because it creates itself as it travels. That’s how it can go through space where there is nothing to push off
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