|
Sorry your right Slice about the slowing. Must be having a black hole morning.
Quote from "Violence in the Cosmos"
Furthermore, contrary to normal intuition, the Theory of Relativity tells us that light always travels at the same speed relative to some observer, no matter what the relative motion of the observer. Thus, light emitted from a moving airplane does not travel with the speed of light plus the speed of the airplane, it travels with the "speed of light", no matter what the speed of the airplane! In a vacuum, light always travels at a speed of 299,792,458 meters per second, no matter how its speed is measured.
Although this seems strange, it has been confirmed in many experiments. These experiments show that it is our "common sense" that is wrong in this case!
To be precise, what we usually call the "speed of light" is really the speed of light in a vacuum (the absence of matter). In reality, the speed of light depends on the material that light moves through. Thus, for example, light moves slower in glass than in air, and in both cases the speed is less than in a vacuum. However, the density of matter between the stars is sufficiently low that the actual speed of light through most of interstellar space is essentially the speed it would have through a vacuum, so we don't make much error by ignoring the difference.
The preceding statements about the constant speed of light refer to the speed of light in a particular medium, such as a vacuum. Within such a medium, the speed is constant, but light changes its speed when it moves from one medium (say air) to another (say glass). This change of speed at the boundary between two different media is the principle that causes a lens in a telescope or eyeglasses to work.
end quote
|