Theoretical Difficulty in the Postulate About Light
In this and the following section, all the "second postulate"
and "postulate about light" are based on our understanding.
Let's think a little bit about the second postulate:
Light travels at the same constant speed in all reference frames.
If two cars are approaching each other, each driver will see the other car as running much faster than its real speed. If you are running to meet a water wave, you are certainly to meet the wave earlier. In both situations, the Galilean velocity addition rule can be used, and the observed speed is higher than that of the source.
Now suppose an observer is trying to meet light earlier by running towards it.
The second postulate says it won't work at all,
because the observed speed of light will always be the same.
Can we find any mechanism to support this idea?
If the observed speed of light is always the same, then that can mean only one thing:
the observer's motion is affecting the light, so that all his/her efforts get canceled out.
Whether light is treated as particles or a wave, do we know of a way to change the speed of light?
Suppose there is one unfound force which can be used to change the speed of light,
so that an observer's motion can be canceled out.
This force must have a magical power, so that whatever the speed of the observer is,
it can always dutifully do its job of canceling.
Now let's put two observers side by side, and one is running toward
the light and the other just sits there waiting for the light to arrive.
This magical force must be able to affect the light facing the running observer
but not the light facing the observer at rest.
Now let the sideway distance between the two observers get shorter and shorter,
so that only one electron can be put in. Now we can see the real power of this force:
it can set a boundary as clear as those in mathematics, so that one side is affected,
but the other side is left alone.
How likely is such a kind of force to be found?