Mach–Zehnder Interferometer

A transport-closure experiment, not a particle-splitting paradox

Claim: Mach–Zehnder tests transport closure, not superposition.
Method: Two anti-correlated reasoning paths that must agree.

Experimental Skeleton

Source BS₁ Mirror Mirror BS₂ D₁ D₂

Path A — Transport Closure Geometry

The two corridors accumulate phases $\phi_1$ and $\phi_2$.

$$ \Delta \phi = k (L_1 - L_2) $$

The second beam splitter recombines transport.

If $\Delta \phi = 0$, transport closes → all detections at $D_1$.

If $\Delta \phi = \pi$, closure fails → all detections at $D_2$.

No object ever splits. Only transport corridors differ.

Path B — Phase Accounting Statistics

Each emission samples an initial phase offset $\theta$.

The interferometer maps $\theta$ deterministically to an output port.

$$ P(D_1) = \cos^2\!\left( \frac{\Delta \phi}{2} \right), \quad P(D_2) = \sin^2\!\left( \frac{\Delta \phi}{2} \right) $$

Statistics reproduce the same closure rule.

Delayed Choice Is Not Retrocausality

Removing $BS_2$ breaks transport closure.

Phase bookkeeping changes at the point of intervention — not backward in time.

The paradox arises only if frames are frozen mid-transport.

Transport-First Resolution

Invariant Connection

The cosine-squared law is the same invariant seen in: