The author argues that in quantum mechanics, it's "impossible to say that an isolated quantum system 'owns' a physical property" in the classical sense. How would you explain this fundamental distinction between classical and quantum properties to a curious high school student, using only analogies from everyday life?

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ch in physics since Newton has been to define objects, to attribute properties to them, and to measure these properties. One then asserts that the object “has” this property, for example that it has a position, a velocity, or a momentum. Does this “natural” approach work in quantum mechanics? Although physicists are extremely reluctant to admit it, the answer is clearly no - and this “no”, correctly interpreted, provides the empirical element that is missing in our understanding of the quantum description of the physical world. So, let’s look at a simple experiment that shows that it is…

Revisiting Quantum Mysteries. Philippe Grangier philippe.grangier@institutoptique.fr Laboratoire Charles Fabry, Institut d’Optique Graduate School, CNRS, Université Paris Saclay, F 91127 Palaiseau, France, Abstract In this article we argue that in quantum mechanics, and in opposition to classical physics, it is impossible to say that an isolated quantum system “owns” a physical property. Some properties of the system, its mass for example, belong to it in a sense close to that of classical physics; but most often a property must be attributed to the system within a context. We give simple…

ame: certainty and repeatability remain, but under more restrictive conditions than those observed in classical physics. If one legitimately considers that certainty and reproducibility are minimum requirements for a realistic description of the physical world, the inescapable consequence of the above observations is that the object to which one must attribute physical properties is not “a system”, but “a system on which a given measurement is made”, since only in this case the result does not change. Such a “contextual” description is an essential difference from Newtonian physics, and it…

a certain and reproducible property of the pair of particles, e.g. that the total angular momentum of the pair is zero. This can be verified in the appropriate context (by making a joint measurement on both particles), but if one performs the measurement in a context where the particles are spatially separated one will obtain necessarily random results (because of the change of context, see above). Still Born’s rule must holds when the context is changed, and for appropriate measurements on entangled particles, it predicts strongly correlated results. This is often related to “quantum…

ere, and one must consider probability amplitudes, which allow one to get a physical picture of Born’s law in this case. The change of context corresponds then to the passage from a representation where the momentum of the particle is defined, to another “incompatible” one where its position is defined. A usual quantum wave-packet is somewhere between these two extremes, but in any case speaking about particles or waves with a classical behavior is a fiction, sometimes useful but most often misleading. The above examples do not necessarily require to fully determine the modalities, i.e. all…