Thomas Young conducted his celebrated double-slit experiment in 1801. Nowadays, quantum physicists pass not only light through screens with slits cut out but also electrons, neutrons, and even molecules as big as the soccer-ball-like fullerene C60. In all cases we see the same kind of interference. Moreover, the interference is observed even if the particles are shot one at a time. However, if the apparatus is modified to register which slit each particle passes through, the interference is destroyed, as shown in figure 1a.
The double-slit experiment, as Richard Feynman observed in his famous Feynman Lectures, “has in it the heart of quantum mechanics. In reality, it contains the only mystery, … the basic peculiarities of all quantum mechanics.” The question we and our colleagues have addressed is whether chemical reactions, studied one collision at a time, display a behavior analogous to that of the particles...
