A brilliant description of the Heisenberg microscope is given by A. I believe the reason that this incorrect explanation is so prevalent is because during the formative years of quantum mechanics, Heisenberg introduced a thought experiment called the Heisenberg Microscope. Even if we had a measuring device which did not disturb the system at all, there would still be unavoidable uncertainty. There is no known reason why the uncertainty principle holds – it just does. The correct explanation is that it is intrinsic to the mathematics of the theory. This is an incorrect explanation of why the uncertainty principle exists in quantum mechanics. Unfortunately, a lot of people go further and try to explain why the uncertainty principle exists by saying that measurements disturb the system. This is the famous Uncertainty Principle. For instance, quantum mechanics says that we cannot know the both the position and momentum of a particle precisely at any moment in time. There are core features of quantum mechanics that can be explained accurately to anyone in a short amount of time, without any “dumbing down”. There is no way of explaining a wavefunction in terms of classical, intuitive physics. The central object of quantum mechanics is the wavefunction, which is complex multivariate function that, when squared, produces a probability density function. Quantum mechanics is harder to explain than classical mechanics because the mathematics of quantum mechanics isn’t easily mapped onto any classical phenomena that people are familiar with. Its sort of like trying to understand how a car engine works – it takes some investment of time, and the more time you invest, the better you start to grasp the ‘mechanics’. Even with basic prerequisites in place (calculus and linear algebra) for me personally it wasn’t until I started my third semester of study that I really felt like I understood the “mechanics” of how the theory works. One of the issues with explaining quantum mechanics to the public is that considerable mathematical prerequisites are needed. It is essential for understanding how semiconductors, lasers, and superconductors work – the behaviour of such systems could not be predicted or described by any prior physics theory. Quantum mechanics can also be used to predict rates of chemical reactions, and material properties such as electrical and thermal conductivity. Quantum theory is a mathematical theory – you start with a system (for instance a hydogen atom, made of a proton and electron), you plug it into equations, and then you calculate things that can be observed (for instance, spectroscopic absorption lines). In this respect, the theory of quantum mechanics is the highest pinnacle of human thought, since it subsumes almost all of reality into a theory based on just a few axioms and equations. Using quantum mechanics we can in principle understand almost everything in the universe, in the sense of being able to predict things. Fortunately, we don’t have to understand why it is to know how to use it to make predictions. As Feynman rightly pointed out, nobody understands quantum mechanics in the sense of understanding why it is the way it is. When I say “understand” I mean that you are able to apply it to make predictions about reality. One of the greatest things about being a physics major is that you learn quantum theory and can proudly say that you understand it. – Richard Feynman, in The Character of Physical Law (1965) “I think I can safely say that nobody understands quantum mechanics.” Explaining the uncertainty principle correctly
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