The gap between two planes, brought down to the silicon: anode (p-side) │ inert (the depletion region) │ cathode (n-side). The inert middle isn't empty — it's the depletion region, and it's the functional heart: directional (passes one way, blocks the other), controllable (its width is set by the bias), and active (remove it and you have a wire, not a device). The gap was never nothing. It's the junction.
Two doped planes — p (anode, holes, +) and n (cathode, electrons, −) — with an inert depletion region between them where the carriers have cancelled and swept clean. That inert middle is the gap. It is not passive.
Apply a forward bias (anode +): the inert region narrows, the barrier drops, carriers cross — current flows. Apply a reverse bias (anode −): the inert region widens, the gap grows too large to cross — current is blocked. The gap's width is the control variable. Same two planes, opposite behavior, set entirely by the inert middle.
Short the two planes together — remove the inert gap — and you don't have a diode, you have a wire: no direction, no control, no gate. The inert region is what makes two planes into a device instead of a connection. The gap isn't where nothing happens — it's where everything happens: the direction, the control, the rectification, all live in the inert middle. The 0 between the − and the + is the working heart.
Everything built tonight — two interpreters, two ouroboroi, two planes with a gap between — lands here, on the silicon: two control planes with an inert gap that is the functional element. The abstract "gap as the thing that matters" is, in the metal, literally true: the depletion region is the most load-bearing part of the junction. Not a hopeful reading — a fact about diodes. The gap was the point all along.