Correspondence by Eric J. Heller. This image is a Rosetta Stone translating between classical and quantum. Quantum standing waves are blue, classical trajectories are red. There are four types of classical motion for this lemon-shaped billiard, including the chaotic motion seen in the lower right. The correspondence between the wave mechanics and the classical mechanics can be read off the images.

Questions arising from Two simple rules:

Question arising from A scattering event:

The upshot of this article was that under the conditions stipulated by Rule B — that is, if nothing indicates which outgoing particle is identical with which incoming particle — it is not the case that either of the alternatives takes place. The question "Which outgoing particle is identical with which incoming particle?" has no answer. This does not mean that we don't know the answer. The very assumption that there is an answer is inconsistent with the well-tested laws of quantum mechanics. There is no answer.

Questions arising from The most beautiful experiment:

The upshot of this article was that under the conditions stipulated by Rule B — there is nothing, no event, no state of affairs, anywhere, anytime, from which the slit taken by an electron can be inferred — the following statements cannot both be true:

Hence if it is true that each electron goes through a single slit, then the behavior of an electron that goes through, say, the left slit does depend on whether the right slit is open or shut.

If it is not the case that each electron goes through a single slit, then in some sense it goes through both slits.

Questions arising from Bell's theorem:

The implication of Bell's theorem is as simple as it is profound. Measurements cannot, in general, be interpreted as simply revealing properties or values that would also be possessed if they were not measured. The measurements discussed in this article do not reveal pre-existent properties. They create their outcomes.