Full Idea
Electrons in atoms move at high speeds, so they are subject to the special theory of relativity.
Gist of Idea
Electrons move fast, so are subject to special relativity
Source
New Scientist writers (Why the Universe Exists [2017], 02)
Book Reference
New Scientist writers: 'Why the Universe Exists' [John Murray 2017], p.24
A Reaction
Presumably this implies a frame of reference, and defining velocities relative to other electrons. Plus time-dilation?