Quantum mechanics (a.k.a. quantum theory or quantum physics) is the fundamental theoretical framework of contemporary physics. This site is devoted to answering a few seemingly simple and straightforward questions such as:

Nodal V. Harvard physicist and digital artist Eric J. Heller creates images which convey the mystery of quantum physics. Here we see an abstracted version of a quantum wave function confined to an infinitely deep pit. The lines along which the sign of the wave function change are called nodal lines. Beyond the red zone, the particle is in a "classically forbidden" realm, and the nodal lines change qualitatively. All works by Eric J. Heller are displayed with the permission of the artist.

Ten years ago Dennis Dieks, professor of the foundations and philosophy of the natural sciences at the University of Utrecht, wrote:

Most physicists have no clear conception of the interpretation of their most basic theory, quantum mechanics. They are largely unaware of the exact nature of the problems in giving a detailed and consistent account of the physical meaning of the theory; and if they are aware, they often don’t care very much. Only very small numbers of researchers have given serious thought to the interpretational problems of quantum mechanics, and have expressed more or less detailed points of view. As can perhaps be expected from the statistics of small numbers, the diversity of opinion is large. Very different ideas have been put forward, none of them supported by great numbers of physicists.

Since the time they were written, these remarks have lost nothing of their topicality. Both the diversity of opinion and the lack of wide support jump out of a recent article in which Piet Hut, Mark Alford, and Max Tegmark discuss the famous matter — mind — mathematics triangle. (Matter appears to produce mind, mind appears to be the creator of mathematics, and mathematics appears to be the foundation of matter.)

Here is how Chris Fuchs describes the situation (in which, according to Dieks, "the only thing that is certain is that familiar concepts do not work"):

Go to any meeting devoted to some aspect of the quantum foundations, and it is like being in a holy city in great tumult. You will find all the religions with all their priests pitted in holy war — the Bohmians, the Consistent Historians, the Transactionalists, the Spontaneous Collapseans, the Einselectionists, the Contextual Objectivists, the outright Everettics, and many more beyond that... They all declare to see the light, the ultimate light...

Dieks again:

The difficulty of developing a convincing interpretation of quantum mechanics can easily be understood. First, the rigorous results which have been achieved preponderantly have a negative character: they are “no-go theorems”. No-go theorems show the impossibility of certain interpretations, but do not themselves provide a new interpretation.... More generally, the outcome of foundational work in the last couple of decades has been that interpretations which try to accommodate classical intuitions are impossible, on the grounds that theories that incorporate such intuitions necessarily lead to empirical predictions which are at variance with the quantum mechanical predictions. However, this is a negative result that only provides us with a starting-point for what really has to be done: something conceptually new has to be found, different from what we are familiar with. It is clear that this constructive task is a particularly difficult one, in which huge barriers (partly of a psychological nature) have to be overcome."

The aim of these pages is to undertake this constructive task, and to understand and overcome those barriers, which are indeed largely psychological.