Current physics describes light as the vibration of an electro-magnetic field that exists throughout space. When this field vibrates slowly, it is radio waves, faster vibrations are visible light, and very fast vibrations are x-rays or gamma rays (Figure 3.5). Visible light is the part of the electro-magnetic spectrum that vibrates about a million-billion times a second, gamma rays are a billion times faster, while radio waves vibrate just a few times a second. All these waves are then the same vibration at different frequencies, so the term light will from now on refer to any electromagnetic wave.
In optics, light moving on an axis is a ray that can polarize in many ways, but filters can produce a ray that is polarized only one way. Lasers can also produce a single pulse, which is one photon at one frequency polarized in one plane.
Such techniques can produce light rays that are out-of-phase, so the crests of one ray can cancel out the troughs of another. Each ray is then separately visible, but they combine to give darkness, as out-of-phase light rays cancel out just as out-of-phase water waves do. This light + light = darkness result confirms that light is a wave, because particles can’t do this. Note that flashlight beams never do this because they aren’t polarized.
Light is also a sine wave, which in mathematics maps to a moving circle (Figure 3.6), so a pointer turning in a circle like a clock hand produces a sine wave as it moves (Figure 3.7). Water waves are also sine waves, caused by forces acting at right angles to the water surface.
.
.
When a water wave arrives at a point on a pond surface, it pushes water molecules up until gravity pulls them back down, then the elasticity of the water pushes them back up, etc. The water molecules move up and down, so corks on a pool just bob up and down as a wave passes. What travels as a wave across a pond is the transverse up-down vibration not the water itself, and this vibration maps to a moving circle.
In theory, light should work the same way, but when an electro-magnetic field vibrates, nothing physical goes up or down in any spatial direction to provide a physical basis for light. Naming a cause doesn’t explain it, so the term electro-magnetic field is just a placeholder for a vibration that isn’t understood. It is then possible that our space is a surface that transmits light waves in three-dimensions just as a pond surface does in two.