Why is there a fault line, an edge, between the world that we see and the world that physicists know really exists beneath its surface? This is one of the deepest problems in the whole of physics, and one that relates to the phenomenon of quantum measurement we introduced a little earlier. When a quantum system interacts with a classical measuring device, such as the polarizing lens in Alain Aspect’s experiment, it loses its quantum weirdness and behaves like a classical object. But the measurements carried out by physicists cannot be responsible for the way the world we see around us appears.
...more
