Some notes on Chapter 3: The Visit to Neg Ahne Poc: A quantum parable

Chapters 4 and 5 give the little bit of background in classical physics needed to understand the quantum enigma. But to give some idea of where we’re going with the quantum, in Chapter 3 we tell a story that illustrates the enlightening bafflement readers should anticipate.

The only way the quantum enigma, the measurement problem, can actually be displayed is by some form of interference demonstration. (The 2-slit pattern provides evidence that each and every object had been in two places. But, by having chosen a different experiment, we could have demonstrated that it was concentrated in one.)

(The correlations displayed in EPR-Bell experiments can be seen as an exception to this interference requirement. It shows another aspect the quantum enigma, but one that still depends on what could have been done.)

The need to discuss interference poses a pedagogical problem: interference is tricky and without motivation at this stage. Moreover, interference is indirect evidence, i.e., circumstantial evidence. That is, we use one fact, the interference pattern, to establish another fact, that the object had been in two places. Circumstantial evidence can, of course, be convincing beyond a reasonable doubt; it can legally establish a conviction.

To display the kind of bafflement the quantum enigma presents us with, we tell the Neg Ahne Poc story. It uses direct evidence instead of the indirect evidence of interference. Therefore, strictly speaking, this story is not actually a display of quantum phenomena. We make the point a couple of times that this story is magic. The physicist-visitor in the story also explicitly says one would need an interference experiment. The story is an analogy to display the same bafflement that the real quantum enigma presents us with. It’s a very close analogy. But it’s worth emphasizing in class that it’s only an analogy.

But we make sure (by repetition) that everyone gets the point, understands why the visitor is baffled. We find that, for a few, it really has to be made very explicitly and repeatedly.