So I understand that light is energy and can be modelled as a wave, where different frequencies are perceived as different colours. All good. But I don’t really understand that. I can understand sound because you can view it as changes in air pressure – and that can explain how sound travels and how it is perceived. But I can’t find anything similar intuitive explanation of how light works – how it is physically manifested, how it travels, and how it can be understood in terms of a wave. Any explanation I can find assumes that you already understand the light as waves concept.
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It sounds like you’re asking what exactly the electromagnetic field is. We describe it using vector fields.
Imagine a fluid, like water or air – except instead of being made of atoms, it’s our old conception of fluids, a true continuum with no smallest parts. At every infinitely small point, the fluid will be flowing in some direction with some velocity. You can represent this with an arrow, except when you try to draw it you can only put down finitely many arrows. However, the fluid flow doesn’t actually have gaps. There are infinitely many points infinitely close together, each with its own direction and velocity, and all together they describe the flow of fluid. Mathematically, we describe this as a function – if you give the function some point in 3D space, it will give you back an arrow describing how fluid is flowing at that point.
This is a vector field. The electric and magnetic fields are also vector fields, but it’s not a vector field *of* anything. Instead, you can think of it as a property of space. Space itself, with no matter in it, ‘knows’ about these two vectors fields – the magnetic and electric fields. Every point in space is pointing in two directions, with their two corresponding magnitudes. The electromagnetic field is the combination of these two vector fields, since it turns out they are deeply related, and it makes more sense to think of them as a single thing instead of two things that interact.
It may seem weird to say that an abstract mathematical function is a thing that exists, but that’s the state of physics these days, and it has been ever since Newton. Instead of nice contact forces between objects, we have to use abstract mathematical entities to create physical models, and they create a rich framework that we can use to explain why human-understandable objects behave the way they do.
An electromagnetic wave is an oscillation in the electromagnetic field. The loose description is that, when the electric field changes, it creates a perpendicular magnetic field, and when the magnetic field changes, it creates a perpendicular electric field. So if you create a change in either one, they will start oscillating back and forth, and this oscillation travels in a direction perpendicular to both of the fields (e.g. electric field is oscillating left/right, magnetic is oscillating up/down, and the direction of travel will be toward you or away from you).
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