© David Kaplan.

This movie illustrates an approximation made to calculate the scattering probability, and final direction, of two electrons. A classical physics calculation would have the electrons, which repel one another, following smooth curved paths. The particles would come together, reaching a point of closest approach before being deflected and moving apart. In the approximation shown here, physicists instead take their interaction to happen at a single point. This approximation gives a relatively accurate account of the scattering, and allows physicists to keep track of the quantum effects. Ultimately, corrections to this approximation ultimately lead to a more accurate description of high-energy electron scattering than the classical picture.