ABSTRACT
Quantum theory characterizes a quantum system by a so-called wave function. Quantum states can be independent of time. Because quantum mechanics offers ‘only’ probabilities for the outcomes of experiments, it is profoundly different from classical mechanics. Quantum mechanics works and appears to be correct, but it does not go as far as X mechanics would go. ‘Hard-nosed’ physicists include many who work on the structure of the nucleus and on elementary particles, those who try to bring about nuclear fusion for the production of electricity, people working on semiconductors, lasers and quantum optics. To them quantum mechanics is a beautiful and reliable theoretical tool, and that is that. Particles collaborating in a single quantum state of a large system are said to be coherent. The wave nature of electrons, and hence of other material particles, having been accepted, the more formal development of a new mechanics had to follow.
