- The standard interpretation of quantum mechanics (known as the Copenhagen interpretation) divides the world into quantum phenomena and classical observers that perform measurements upon the phenomena. This provides a quite functional framework for calculating probabilities of measurement outcomes, but it lacks the generality necessary for such things as retrodiction, and examination of situations in which there cannot be classical observers.
Enter the consistent (or decoherent) histories formalism, which provides a consistent framework for assigning and interpreting quantum probabilities even in the absence of classical observers. In order to aid others in adopting the formalism, I herein examine the double-slit experiment within the framework of the consistent histories formalism.
For my first trick, I replicate the results of basic geometric optics applied to Young’s experiment. Second, a detector model is included to make the interference pattern vanish, demonstrating the shift from wave behavior to particle behavior. Finally, certain approximations are removed to examine the case of non-infinitesimal slits. By not appealing to the outside world of observers, the consistent histories formalism is ideally suited for demonstrating the link between persistent records and the transition to the classical realm, crossing smoothly through paradoxical domains where a particle can diffract like a wave.