Six Impossible Things: The Mystery of the Quantum World

by John Gribbin

In 2008, Pozzi and another group of colleagues took a step further. They developed an experiment in which electrons could be fired one at a time through two genuine, nano-sized physical slits in a thin screen, to be detected on the other side in the usual way. As expected, the electrons arriving at the detector screen built up an interference pattern. But when the Italian team blocked off one of the slits and carried out another run of the experiment, there was no interference. The pattern on the detector screen was a simple blob directly behind the slit, just as you would expect to be produced by a stream of particles. How does an individual electron traveling alone through the experiment, through a hole in a wall, “know” whether there is another hole nearby that it might have gone through, and whether that hole is open or closed, and adjust its subsequent flight path accordingly?