I just got back from Copenhagen, a city with a lot of science history. For example, next month marks the 100th birthday of the Bohr model for the structure of atoms. This was developed primarily by Niels Bohr at the University of Copenhagen as was way to better explain how the electrons and protons are arranged in matter. The Bohr model is almost a requirement in most introductory physics and chemistry classes, despite the fact that its has several important shortcomings that can only be fixed using a completely quantum mechanical treatment, as opposed to the “semi-classical” approach taken by Bohr. I think the reason is that it is “mostly right,” (especially compared to previous attempts like the “plum pudding model“) in the sense that the electrons in atoms are confined to specific orbits around a positively charged nucleus, and more accurate models require quantum mechanics that is much more mathematically taxing and difficult to visualize.

The city itself is also the namesake for the “Copenhagen Interpretation” of quantum mechanics. This was developed by Bohr and Heisenberg and attempts to explain the weirdness of quantum mechanics by saying that it does not refer to an objective reality, rather, QM is a mathematical tool that allows us to calculate the probability of any event. A few, somewhat unsettling consequence are the concept of “wavefunction collapse,” in which the probability function of a particle instantly changes everywhere in the universe when we make a measurement on that particle. In addition, the Copenhagen Interpretation holds that questions like “where was the electron before the measurement?” are not meaningful. All we can say is there is a function that indicates the likelihood of finding the electron at a particular location if we look. Again, this is the way virtually all introductory classes are taught, despite the shortcomings that may be fixed in more complicated interpretations, including Quantum Bayesianism.

The Tycho Brahe made astronomical observations from the “Round Tower,” the oldest such tower in continuous use.

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