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Two cents from an experimentalist. It is always good to keep in mind that a wavefunction for a real particle in the lab is a solution of Schrodinger's equation with specific boundary conditions given by the experimental setup that makes the measurement. Every measurement changes the boundary conditions for the solution that describes the particle's ...

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The electron doesn't get destroyed when you measure it (though photons usually do), but its wavefunction doesn't go back to how it was before. Instead it gets a new wavefunction, different from the old one. If you measured the position of the electron, this new wavefunction will be a delta function (a single infinitely sharp spike) centred at the position ...

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Assuming wave-function collapse is correct (which can be a relatively hefty philosophical claim in some circles), then think of measurement this way: When you measure an observable on a system, you collapse the wave-function of the system into a Dirac delta function in the eigenbasis for that observable. If you measure position, you get a delta function in ...

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In practice, the apparatus measuring the spin should be localized somewhere in space (it cannot fill the whole universe!) and this fact implies that you always make a measurement of position (actually very rough in general), even if you are measuring the spin. Suppose that $\Omega \subset R^3$ is the bounded region in $R^3$ where the apparatus is localized. ...

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Very intuitive. No maths. There is an excited state with a symmetrical probability distribution and no e/m dipole moment. There is a ground state (or less excited state) also with no dipole moment. There is a tiny probability that the excited state electron will be in the ground state that allows both states to be present at the same time producing a finite ...

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