© David Kaplan.
The electron on the left has an effective rotation that is counter-clockwise when looked at along the direction of motion (i.e., from behind). The mirror image is an electron rotating clockwise when seen along the direction of motion. Physicists call the former left-handed and the latter right-handed. Because the weak force treats the left-handed electron and right-handed electron differently, the world inside the mirror has different interactions than our world! (Unit: 2)