Having performed the single-photon-at-a-time version of the double slit experiment 45 years ago, I’ve been trying to make sense of it ever since (mainly in the shower). I came up with this interpretation of the double slit experiment: The photon is in a superposition of paths-taken after it traverses the slits. If the single-photon-at-a-time result is truly the same as the classical interference pattern, the photon cannot then immediately resolve the superposition and choose a direction to the screen probabilistically. If it did, the photon would then travel in a straight line to the screen (being notoriously reluctant to deviate from a straight line) while the classical interference fringes would trace a hyperbolic “path” to the screen. (Weirdly and coincidentally, the other time photons deviate from a straight line is when passing by a massive object’s gravitational field and in that case it also describes a hyperbola.)

So the photon must exist as a wave function until it reaches the detection screen where it then “throws a dice” to determine where it will be detected. Simple.

In trying to understand superposition, I tried to understand the results from entanglement. I figured that with entanglement, since the result of measurement of each particle was random and assuming that there was no spooky action at a distance and that information couldn’t travel faster than c, the measurement result for each particle must be able to accommodate the result from the other particle.

The fact that the two observations are independently undertaken means that each observer’s observation cannot influence the outcome of the other’s observation but the other outcome is nonetheless determined by the outcome of each observer’s observation. Two worlds must be created by an observation so that both possible outcomes exist to accommodate the independent outcome of the other’s observation. No spooky action here.

To take an example of a pair of electrons, each a superposition of up and down spins, when the spins are measured there are four possible results representing four potential worlds (up up, up down, down up and down down). When a pair of electrons are entangled so that their spins, although not determined, will be opposite when measured, these four possibilities are reduced to two potential worlds (up down, down up). It’s as if a quantum exclusion principle has prevented the two particles from occupying the same state during their close interaction

So when the pair are then separated and the spin of one is measured, the world splits at that location and the observer also splits and will experience being in one of these two worlds. If a measurement is taken of the other electron, the world splits at that location and that observer will experience being in one of the same two worlds. When news of the outcome travels from one location to the other it travels to the world where the electron spin is in the opposite direction. The influence travels from one location to the other at the speed at which the worlds split. I guess there is a connection between the entangled electrons - it is the "line" along which the world will split. Since the “news” of the result can travel at c, the split must also travel at least at c.