## Unified Electrodynamic Force

The magnetic force is nothing more, and nothing less, than a direct consequence of Einstein's theory of relativity.

Fire two charged particles at the same moment, with the same initial velocity, into a perfect vacuum (Figure 1). The two particles, having the same electric charge, repel one another. This repelling electric force, F, makes the particle tracks diverge. Given the magnitude of the electric force and the masses and internal velocities of the particles, you can, if you know a little college physics, predict the rate of divergence—but you'd be wrong. The actual particle tracks diverge at a slower rate than electric-field considerations alone predict.

If French physicist and mathematician André-Marie Ampère were alive today, he would explain the diminished divergence as the result of magnetic forces. Ampere's laws describe a mechanical force that pulls together parallel wires carrying current in the same direction. Simplified to the case of two charged particles moving in space, the pull of Ampere's magnetic force partly counteracts the electric repulsion to produce the actual trajectories shown in Figure 1. 