The speed of light is constant. No matter how we measure it, it always returns the same value. This value is the constant c. Some will argue that this is true only for light travelling through a vacuum. However, the reason light appears to slows down in transparent media such as glass and water, is not due to any change in speed, but a change in path length. Photons meander through such media, rolling past atoms like slalom skiers. The speed of motion is the same, but the path is longer, and hence we get the situation where photons appear to slow down as they enter such media and speed up as they come out of them.
Photons, and neutrinos, always travel at the same speed. The only reason there sometimes seem to be a difference is that smaller, less energetic, particles can travel in straighter lines than bigger more energetic, particles. Neutrinos appear to travel a tiny bit faster than light because they are smaller. The same is true for red photons compared to the more energetic blue photons.
The reason no photon or neutrino can travel faster or slower than all other photons and neutrinos is that the speed is determined by the aether, which locks in the speed so that it is equal for all.
Some may argue that the speed of light could nevertheless change, provided all photons and neutrinos do so together. But this would ignore an important aspect of how speed is measured, and how time is related to the speed of light. As we will see, time is tied up to the speed of light in such a way that all measurements of it will yield the same result, no matter what. The logic goes as follows:
- To measure speed, we need a known distance and an accurate clock.
- The way a clock works is that it has something moving at a predictable rate. This requires energy to move around in a system, usually as a vibration of some sort, or some form of nuclear decay. Either way, energy is communicated between elements of the clock. This is true for all clocks, mechanic, electric, nuclear or biological. All involve energy displacements.
- Now, once we realize that energy is communicated either by photons or neutrinos, both moving at the speed of light, we can see the impossibility of measuring any change in c. If photons and neutrinos were to slow down, our clocks would slow down with them. If they were to speed up, our clocks would speed up too. The speed of light, which can only be measured with a ruler and a clock, must therefore yield c regardless.
This makes c a fundamental constant, determined by the aether, and tied directly to the concept of time itself.