The Department of Physics at the Faculty of Science, in collaboration to the Physics Department at the Junior College, is organising a public talk by Prof. em. Dr Urbaan M. Titulaer. Prof. em. Dr Titulaer is from the Institute for Theoretical Physics at Johannes Kepler University in Linz, Austria.
The public talk, entitled 'Does God Really Play Dice? The role of probability in quantum mechanics', will be held on Friday 17 March at 18:30 in Room 401 Maths and Physics Building (MP401).
Prof. Titulaer will discuss some basic aspects of Quantum Mechanics that have characterised the subject from the beginning, but that have become accessible to experimental study, and gained relevance for applications, only recently.
A central characteristic of Quantum Mechanics is the role played by probability. In classical physics, probability enters when there is incomplete information about a system. In Quantum Mechanics probability appears to be intrinsic, though some physicists, beginning with Einstein, kept hoping that a deeper, deterministic theory (a so-called hidden variable theory) would eventually be found; Einstein expressed his view by the famous quote 'God does not play dice'.
A second characteristic is complementarity: Heisenberg noted that it is impossible to prepare a quantum system in such a way that all its properties can be predicted with certainty: if some properties are well determined, other properties, called complementary ones, must have a minimal uncertainty (Heisenberg´s Uncertainty Principle). Examples of complementary properties are position and velocity of a particle, or different types of polarisation of a photon (light particle). Although in Quantum Mechanics complementary properties cannot be both well determined, one may hope for hidden variable theories, in which this is the case, though at a level as yet inaccessible to our experiments. For single particles such theories appear to be possible. Their predictions are identical to those given by Quantum Mechanics, so they cannot be verified, but they may contribute to our peace of mind.
However, when two particles are generated simultaneously, correlations between their properties will in general occur. The specific aspect for quantum objects is that correlations may exist in complementary properties as well; this is called entanglement. The correlations may persist even when the particles have moved far apart. Thus, when a property of one particle is measured, information about the other, far removed particle is instantaneously obtained. Einstein refused to believe in such 'spooky action at a distance', but the predictions have meanwhile been confirmed experimentally. The results can be proved to be incompatible with hidden variable theories unless such theories violate other fundamental principles of physics, such as locality or causality. Thus, experiments on entangled particles indicate God may play dice after all.