Light, Electricity, and Magnetism

Abstract

In the first two chapters, we reexamined basic concepts such as space and time starting from the most basic level. The philosopher Kant thought that these things would need to have been built into our brains in order to enable us to grasp the world around us. How did Einstein get the idea for his theory of special relativity? There was a road map at hand, a blueprint of what was to be expected: that was, and still is the theory of moving electrical charges, namely, electrodynamics. The reason is simple: while mass, time, and length change with speed relative to the observer, electrical charge is absolute, as is the speed of light. We will demonstrate this by a simple example, a straight wire carrying an electric current. We will see why the magnetic field around this wire exhibits relativity in everyday life. This example was the starting point for the theory of special relativity.