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In quantum physics, a particle can be in a superposition of two states until it is measured. In other words, the aforementioned particle doesn't have a definite state until it is "looked at" (measured). A superposition state is a state. So a particle in such a state does have a state before being measured. Since certain properties (i.e., an ...

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A superposition is a perfectly valid state in quantum mechanics. It simply doesn't have a correspondence in classical physics, which is the result of quantum mechanics (and not the other way around!). "In other words, the aforementioned particle doesn't have a definite state until it is "looked at" (measured)." Yes, the particle (or better "the ...

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The question you ask is a tough one and everyone has his own opinion about the answer (look at the comments of your question). In particular, one has to adopt a more or less clear philosophical position about what science ought to tell us in order to reply. That being said, the decoherence programme tries to address some of the questions you wonder about. ...

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MWI has issues with how the effect of a measurement causes the world (universe) to split into potentially an infinite number of copies of itself, each slightly different. How fast does the influence "rip" (tear?) through the Universe? At the speed of light? No, it would have to be faster otherwise ERP experiments would not work. So, instantaneously? But in ...

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Like everything of importance in physics it's an experimentally testable fact. If it wasn't, we wouldn't be talking about it. Secondly it is, of course, built into the theory, otherwise the theory wouldn't be correct. What it is NOT, is a measurement "problem".

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It has obviously been experimentally tested many times, but it's also derivable theoretically from the mathematics of quantum mechanics. Two basic ideas are important here--the first is the notion of a Fourier series, which allows you to represent any arbitrary periodic function (a square wave, for example) as a potentially infinite sum of different sine and ...

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It is actually a mathematical law, for conjugate operators. For any two operators the following applies: $$\langle (\Delta A)^2 \rangle \langle (\Delta B)^2 \rangle \geq \frac{1}{4}|\langle[A,B]\rangle|$$ So for conjugate coordinates this means the Heisenberg uncertainty principle - for more detail - see Sakurai Chap. (supposed to be a remark but ...

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Here are some random references out of the top of my head. I recommend chapter 8 of the book of Schlosshauer - Decoherence and the Quantum-To-Classical Transition. Also in favor of the MWI, see the book by David Wallace - The emergent multiverse, which addresses also open problems and discusses some criticisms. Also see: ...

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None of the interpretations are right or wrong, since they are interpretations of the same mathematical formalism which predict the same events. Interpretations are a philosophical adjunct that provides a "what is REALLY happening" view. If an interpretation is tested and shown to be wrong, then it is no longer an interpretation - just wrong physics. ...

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If in the Stern-Gerlach experiment we prepare an ensemble of particles in a superposition of spin up and spin down with respect to the z-axis and you could predict in every instance if we would obtain either spin up or spin down with respect to this axis but still reproduce the statistics corresponding to that superposition, there would at first sight be no ...

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When the first observer performs the measurement the result will be an eigenvalue of the corresponding observable being measured (e.g. if an electron's spin is measured the result will be either +1/2 or -1/2). Now the system is in the corresponding eigenstate of the observable which was measured (e.g., either spin-up or spin-down). If this is also the ...

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