Relativity and the Origin of Magnetic Fields

This article provides an intuitive explanation of the origin of magnetic fields, avoiding the typical textbook approach of simply introducing 'B-fields' or 'H-fields'. Using a thought experiment involving a spaceship and flashing lights, the author elegantly explains how relativistic length contraction accounts for the appearance of magnetic fields when electrons move in a wire. The key insight is that while a stationary observer sees a constant electron density, an observer moving with the electrons perceives a lower electron density and a higher positive ion density, resulting in a net electric field pulling it towards the conductor – the essence of a magnetic field.