How light can travel without any medium?
Answers
Normally, it is said that transverse waves require a relatively rigid medium in order to transmit their energy. However, another way to categorize waves is on the basis of their ability or inability to transmit energy through a vacuum (i.e., empty space). Categorizing waves on this basis leads to:
electromagnetic waves — an electromagnetic wave is a wave that is capable of transmitting its energy through a vacuum (i.e., empty space)
mechanical waves
Electromagnetic waves are produced by the vibration of charged particles. And, all light waves are examples of electromagnetic waves. So, yes, mechanical waves require a medium in order to transport their energy from one location to another, but electromagnetic waves are produced by a vibrating electric charge. And, think of it this way that as such, they consist of both an electric and a magnetic component.
So okay, if you fail to find a mental model for them, then I’ll suggest that the closest one seems to be a rope: if you wobble a wire holding it by its end, it will oscillate in a sine-like pattern. You see it as a 1D field oscillating in a second dimension. Thus, a wobbling wire is a 2D structure. However, this ‘wobbling rope’ idea, which I bring up as it if could be a great depiction of a light wave, is actually, I think, a poor metaphor. Because the medium of a rope wave is a rope itself, and a rope is kinda 1D (in the sense that it’s a line). But what about light? Well, when a light wave travels through its field, it looks like it occupies an 1D line of a 3D field. This line wobbles in two extra dimensions (radial polarization), and so we say that light waves can be radially polarized and they are depicted as a spiral.
Also, actually, photons don't follow any lines. They are emitted in one place and absorbed in another, between that there is quantum electrodynamics, which certainly doesn't have anything resembling "lines". So okay, it’s not exactly like when a wave travels through a rope. You know, the rope goes up and down, the position of all the 'rope-particles' changes, they oscillate and this makes up the wave. It’s not exactly like that, because with light, it is the electromagnetic field oscillating.
When going to the underlying quantum mechanical level, light is composed by an enormous number of photons (elementary particles) which in synergy build up the classical electromagnetic wave. In a sense photons are the medium on which the classical wave rides. How this happens is a matter of understanding quantum field theory. It so happens nature is at the basic level quantum mechanical and the classical light emerges from the underlying quantum mechanical level of zillions of photons with wavefunctions and probabilities in superposition to form the classical electric field. You have to know quantum field theory basics to understand the mathematics.
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