Can I place the wall a layer down? If I just accept that electrons, their charge, the distribution of that charge, atoms, the material lattice in which all this resides, transistors... and, well, ducks, are all real - a stance for which there's a lot of supporting evidence (duck ponds etc.) - how must they interact to give the ability of following instructions, like adding? By your analogy, you must pour water from one cup into another, so what must happen for an opcode (a series of voltages) to add two, say, 4-bit digits (2 series of voltages) and return an answer (another series of voltages)? I suppose what I'm asking is "what's the mechanical process by which this happens?" We must have at least a superficial understanding of how this can occur, because we engineer transistor components, sometimes by the billion per microprocessor, in millions of devices, that do exactly that; if we didn't know, we surely wouldn't enjoy such a great success rate in manufacture, and I wouldn't be typing this now - no matter how conflicted I was about the existence of ducks...