A team led by the Austrian physicist Anton Zeilinger has now carried out an experiment with photons, in which they have closed an important loophole. The researchers have thus provided the most complete experimental proof that the quantum world is in conflict with our everyday experience. The results of this study appear this week in the renowned journal Nature (Advance Online Publication/AOP).
When we observe an object, we make a number of intuitive assumptions, among them that the unique properties of the object have been determined prior to the observation and that these properties are independent of the state of other, distant objects. In everyday life, these assumptions are fully justified, but things are different at the quantum level. In the past 30 years, a number of experiments have shown that the behaviour of quantum particles – such as atoms, electrons or photons – can be in conflict with our basic intuition. However, these experiments have never delivered definite answers. Each previous experiment has left open the possibility, at least in principle, that the observed particles ‘exploited’ a weakness of the experimental setup.