Crossing into a mirror world: Particles turn to wisps of fog, and the magnetic monopole paradox dissolves

In Goethe’s ballad “Erlkönig,” immortalized in Schubert’s fevered 1815 setting, a dying boy riding through the night sees a spectral king beckoning from the darkness. His father calms him: “Mein Sohn, es ist ein Nebelstreif”—my son, it is only a wisp of fog. In the poem, the father’s reassurance proves tragically wrong. In the quantum world, however, his words acquire an uncanny new meaning.