Dear friends -- Pedro informs me that as "lecturer" I'm allowed four responses per week. Not having kept track very well, I take this opportunity to answer some questions, and will start a fresh count on Monday -- if that's OK.
Gordana -- l am out of my depth in a discussion of phenomena/noumena/Dinge-an-sich. But when I agree that the Higgs exists out there in the world, I am sure it's not an object like a marble, but a symbol for a collection of experiences that many people have had, and have discussed, and codified, so that if they perform another experiment where it might play a role, they can be prepared with betting odds for what they might experience next. Joseph -- "the electron is a point" means that no experiment to date has found evidence for a finite size. In the theory (quantum electrodynamics) there is no room for any parameter with dimensions of length, although there are mass, charge, spin, and magnetic moment. When you introduce a finite size into the theory, it makes wrong predictions. (This is not true for protons, for example.) "The gravitational field lives in 3D" was not supposed to deny that Einstein's elegant formulation treats time as a fourth dimension. But a "quantum field" is an altogether different and much more complicated beast which lives in infinite dimensions, and has no analog whatever in our everyday human world. Stan -- Is quantum mechanics meaningless? Not if it is regarded as a recipe for manipulating nature successfully for good or ill. The philosophical attitude that is most close to QBism is probably pragmatism: Truth is what works. Lars -- How does QBism differ from Copenhagen? This is a crucial question. It differs not at all in the formalism, and only subtly in the interpretation. Many users of quantum mechanics regard the wavefunction as a real property of an electron. They talk about "the wavefunction" in the same way you might say "the speed of the car." They must then deal with perennial problems such as action-at-a-distance and the "collapse of the wavefunction". QBists regard the wavefunction the way Bruno de Finetti regarded probability, when he wrote, in caps, PROBABILITY DOES NOT EXIST. I think he meant that the probability of a coin falling heads is not a measurable property of a coin. All it is is a personal belief of how much an agent should bet. And that belief changes instantly and locally when you make a measurement, or hear that someone else has made one. Some people call the he Copenhagen wavefunction ontic, the QBist one epistemic. Thank you for making me think these things through -- though it's hard work! Hans
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