Why does quantum interference feel mysterious? Blame loop geometry.

Quantum interference — the spooky part of the double-slit experiment — is usually treated as a strange feature of overlapping wavefunctions. This work shows it follows inevitably from unitarity: probability decomposes into closed loops of forward and reverse amplitudes, and the Born rule's squaring structure reflects exactly that loop geometry. Bargmann invariants, previously introduced by hand, emerge naturally as the phase-independent labels for each loop class.