26.7 Einstein’s special theory of relativity

In this post, I am returning to the subject of relative motion, that I first described in posts 16.4 and 16.12. But we shall see that this description is complicated by what I wrote in post 26.6. According to post 26.6, the speed, c, of an electromagnetic wave (for example, light), in a vacuum, is given by where ε0 is the permittivity of free space and μ0 is the permeability of free space. Since we consider ε0 and μ0 to be fundamental constants, we would then expect c to be a fundamental constant. Let’s think about this in a bit more detail. The constants ε0 and μ0 enable us to calculate forces arising from electromagnetic phenomena. These forces determine the state of motion of an object. According to the Galilean principle of relativity, the state of motion of an object (for example the time period of a pendulum) is the same in all inertial frames of reference. Since I first described this principle, in post 16.4, I have covered a lot of mathematics which help us to understand it…