Critical analysis of Popper’s experiment

An experiment which could decide against the Copenhagen interpretation of quantum mechanics has been proposed by K. Popper and, subsequently, it has been criticized by M. J. Collett and R. Loudon. Here we show that both the above-mentioned arguments are not correct because they are based on a misuse of basic quantum rules.

Figure 1

Initial arrangement of Popper’s proposed experiment. The black vertical lines determine the width of the slits; the sequence of vertical gray boxes represents the array of counters behind the slit.

Figure 2

Analogue of Fig. 1 for the case in which the slit at $R$ has been remarkably narrowed. After the slit the scatter in position increases remarkably.

Figure 3

Explicit example of a correct Popper-like experiment we are discussing. We have represented explicitly the three correlated Gaussians appearing in the wave function. One has to keep in mind that we have assumed that the width $\sigma$ of these Gaussians is much smaller than their separation $\alpha$, a fact which cannot be represented correctly in the figure.