The predictions of quantum mechanics agree very well with experimental data. Up to date there is no evidence for any domain in which quantum theory breaks down. Even its relativistic descendants agree marvelously with experiments, among which quantum electrodynamics (QED) is considered to be the most stringently tested theory in the history of physics. Nevertheless, almost every one of us is baffled when being first introduced to the theory of quantum mechanics. More remarkable is the fact that although the theory became the core of mainstream physics so rapidly, most of its founders were never fully content with its ontological implications. This dissatisfaction can be best demonstrated by the Nobel laureate Murray Gell-Mann who said:
Quantum mechanics, that mysterious, confusing disciplines, which none of us really understands but which we know how to use.
In the last few decades we have witnessed the remnants of the famous Bohr-Einstein debate slowly decaying, as the great majority of physicists fully accept the Copenhagen interpretation of quantum mechanics. Whenever any doubts about quantum mechanics arise, it is often argued that quantum physics requires a radical revision of our world view, as our intuition from interacting with the macro-world cannot be expected to hold for the micro-world as well. It was Richard Feynman who said to his quantum mechanics students:
That's the way nature works. You don't like it? Go somewhere else! To another universe where the rules are simpler and philosophically more pleasing....
I do not share this view at all. This objection of mine to Feynman's words is one of the reasons for the existence of this codex.
Even if the predictions of quantum mechanics coincide with experiments, it does not mean that basic questions concerning its foundations should not be asked. On the contrary, the fact that quantum mechanics is so successful should encourage us to stop and rethink its philosophical implications. Quantum mechanics provides us with a great tool for computing probabilities of experimental results, but gives little (to no) insight about reality per se.
The goal of this codex is to analyze and discuss the theoretical, experimental and philosophical foundations of quantum mechanics.
Besides the Copenhagen interpretation, there are alternative interpretations of quantum mechanics that give far better intuition to the physics of the micro-world. These interpretations include Bohmian mechanics and stochastic mechanics, both of which will be discussed as well. From the alternatives, I am particularly fond of Bohmian mechanics. The measurement process, one of the most controversial issues in the Copenhagen interpretation, turns out to be one of the most appealing aspects of Bohmian mechanics, as in Bohmian mechanics reality receives an objective description independently of whether or not we observe it.
Must the quantum world be so mysterious?