Abstract

We have already seen what happens in a typical experiment in quantum physics. When an observation is recorded say on a phosphor screen or photographic plate quantum entities (like photons or electrons) will appear as particles in precise positions. But their observed distribution is predicted by Schroedinger's wave function, and in appropriate conditions they exhibit Airy's wave associated ring pattern. This suggests that while unobserved they were behaving as waves which can spread out in more than one direction at once but once they are observed, they have just a single position, a characteristic of a particle. The act of observation "collapses the wave function" and an actual state precipitates, as it were, out of the cloud of previously possible states. This is what scandalized Einstein: that the chance event of an observation should not merely uncover but actually create the reality of the universe. But the question arises: what is so special about a device such as a light sensitive plate, that its interception of a quantum entity should count as an observation and so "create" actuality in this way?