I'm trying to at least understand what decoherence can and cannot explain about how quantum mechanics works, the more I read, the less clear I am about what is known and what is merely speculative. So I finally decided the only way to get any further was to try and clarify what I think is known, and give others an opportunity to confirm or correct as the case may be. The fundamental mystery of quantum mechanics is that the basic equations tell us that any isolated quantum system evolves deterministically in accordance with a unitary equation, but in practice, the transition from microscopic to macroscopic environments appears to engender a 'collapse', turning waves into localised particles, and doing so in a probabilistic way. The second mystery of quantum mechanics is that macroscopic superpositions of very different states, such as Schrodinger's Cat, can easily be described within the mathematical formalism, but appear not to exist in the real world. As I understand it, decoherence provides what might be described as a mathematically suggestive explanation of the second point. Essentially, as soon as a system gets big enough, the complex interaction of a macroscopic number of things causes macroscopic superpositions to be extraordinarily unlikely and unstable configurations, in much the same way as modern interpretations of the second law of thermodynamics describe entropy-lowering events as staggeringly uncommon, rather than theoretically impossible. This particular aspect of decoherence appears to be fairly well accepted by many people, and has some support from entanglement experiments, the behaviour of quantum computers etc. Although decoherence arguments make it plausible why we never see macroscopic superpositions, it appears at first sight to offer no explanation of the first question. If the apparent collapse of the wave function is simplly an inevitable consequence of the interaction with the rest of the universe, or even a fairly small but macroscopic part of it, then why isn't that a determinstic process, i.e. where does the quantum randomness come from. What appears to be randomness could in fact just be extreme sensitivity to the initial conditions. In other words, when an electron goes through two slits at once it's behaving as a wave. When it goes through only one slit and gets measured, it's still behaving as a wave, one which decoherence has concentrated in a small area through interaction with the other particles in the apparatus. But exactly where that concentration will occur, although deterministically calculatable in theory, is in practice so sensitive to intiial conditions and to unknowable ones at that ( the complete starting states of everything in the universe which could influence the result ), that an element of ramdomness appears. But in this case, quantum randomness is just like classical randomness, albeit computationally even worse by some humungous factor. And so we appear to have an explanation of all quantum wierdness. The entire universe is deterministic, but the emergent behaviour of small parts of it can only be analysed statistically. Einstein was right. God does not play dice with the universe - ( just with almost all parts of it :) Have I gone too far. Am I imputing to decoherence more than there is evidence or even an analysis for? Can anyone point me to an analysis of a gedanken experiment in which decoherence can demonstrate a chaotic-like behaviour, or, even better, some indication that this kind of localisation caused by entanglement is inevitable in practice, rather than simply plausible. And if my understanding above is in fact what decoherence tells us, then where has the mystery gone, and why do people still advocate alternate, almost philosophical approaches?