In current physics, light is the vibration of an electromagnetic field that exists throughout space. When this wave vibrates slowly, we observe 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 electromagnetic 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” can apply to any electromagnetic wave.
In optics, light moving on the same line is called a ray of light. A single point of a light ray still has many photons polarized in many different ways, but filters can produce a ray that is polarized only one way. Lasers can also produce a light pulse that is one photon with one frequency polarized in one plane.
Such techniques can produce rays of polarized light that are out-of-phase, so the crests of one ray are the troughs of another. Each ray is then separately visible, but they combine to give darkness, as the out-of-phase rays cancel each other, just as out-of-phase water waves do. This light + light = darkness result confirms that light travels as a wave because particles can’t do this. Note that flashlight beams can’t do this because they aren’t polarized.
We also know that light is a transverse sine wave, which in mathematics maps to a moving circle (Figure 3.6). A pointer turning in a circle like a clock hand produces a sine wave, as shown in Figure 3.7. Water waves are also sine waves, caused by forces acting at right angles to the water surface.
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When a water wave arrives at a point on a pond surface, it pushes the water molecules up until gravity pulls them back down, then the elasticity of the water pushes them back up, etc. The wave just moves water molecules up and down, so corks just bob up and down as a wave passes. What travels as a wave across a pond is then a transverse up-down vibration, not the water itself.
In theory, light should operate in the same way, but in current physics, electromagnetic waves are imaginary, because no-one can specify what physically goes up and down, or give a physical direction for it to so. Physics says that an electromagnetic field vibrates, but there is no physical basis for that. Naming a cause doesn’t explain it, so the term electromagnetic field is just a placeholder for what we don’t know. It is now suggested that space is the surface that transmits light as a wave, just as a two-dimensional pond surface does, but in three-dimensions.