Electromagnetic Waves

Sound needs air, water waves need water, but light crosses 150 million kilometers of empty space to reach you from the Sun. It can do that because light is not a disturbance in a substance at all. It is a disturbance in the electric and magnetic fields themselves. A changing electric field creates a changing magnetic field around it. That changing magnetic field, in turn, creates a changing electric field farther along. Each field regenerates the other, over and over, and the pair moves forward together at the speed of light, roughly 3.00 x 10⁸ m/s in vacuum. No material is required because fields are not made of matter, they are regions of space where charges feel forces, and those regions can change and propagate on their own.

Picture the wave moving along, say, the x-direction. The electric field oscillates up and down in the y-direction, the magnetic field oscillates in and out of the page in the z-direction, and both are perpendicular to each other and to the direction of travel. This is a transverse wave with two fields riding together, locked in step, one creating the next instant of the other.

This connects to the rest of the unit because once light is just an oscillating field, everything you already know about waves, superposition, interference, diffraction, applies to it directly. An antenna makes this vivid: shake electrons back and forth in a wire and their acceleration launches a changing electric field, which hands off to a magnetic field, which hands off again, and the wave detaches from the antenna and keeps traveling outward forever, independent of the source that made it.