Harry M. Quiney

Quantum vacuum resembles a sea, constantly rippling with tiny splashes. An electron in an atom moves in this sea, and its path slightly changes due to the waves. Previously, such corrections were accurately calculated only for hydrogen-like ions with a single electron. But in highly charged ions with several electrons, the picture becomes more complex.

A mapmaker drawing a route through a city doesn't sketch every brick in every wall. Streets, intersections, and distances are enough. The same goes for calculating radiation dose in breast tomography: you don't need every cell, just a faithful overall picture.