I Quantum Jumps and Schrodinger's Cat are predictable

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A. Neumaier

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Sigh. As I said, it's very clear in which sense the notion of "quantum jump" is meant. It's NOT the outdated view a la Bohr within "old quantum mechanics". It's the transition between energy eigenstates of some Hamiltonian due to perturbation.
Yes, and everybody in this thread except you understood it in this way. You alone ranted against the name. You want to reserve the name quantum jump for Bohr's old understanding, but others find the term far too descriptive to put it permanently to rest.
the spontaneous emission of a photon in that case is not a quantum jump of "old quantum mechanics" but a dynamical process as any other in QED, and for sure it's not instantaneous.
This non-instantaneous dynamical process is called in modern quantum optics (and already long ago) a quantum jump. (As any jump in real life it takes time, but can often be idealized as being instantaneous.)

In quantum mechanics (which can be used without invoking QED), the quantum jump is represented by a collapse of the state (another very common term that you decree to be taboo) when a small quantum system passes a filter where it undergoes scattering, or when a single atom is manipulated in an ion trap.

If you would stop fighting for your ideosyncratic restriction of this common terminology in the scientific literature on quantum mechanics, some of the repetitive overhead in the foundational discussions would go away.
 

vanhees71

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This socalled "collapse" is also a dynamical process, not a quantum jump and nothing that's outside of the dynamics of QT.

Of course, in non-relativistic QM you can enwoke instantaneous processes as an "explanation" without being in conflict with causality, but you cannot do so within relativistic local microcausal QT, because that would be a contraction.

I think it's very important to emphasize this point, and if it comes to debates on the foundations, the use of clear and unambiguous language is utmost important. That's why in my opinion one should not use some of the (in my opinion unfortunate) standard notions in the scientific literature (among them "quantum jumps", "collapse"). Even worse are philosophical notions like "realism"...
 

A. Neumaier

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This socalled "collapse" is also a dynamical process, not a quantum jump and nothing that's outside of the dynamics of QT.
Of course. But it is a dynamical process of QED, and must therefore be postulated explicitly in simple quantum mechanics for nonexperts.

That the collapse cannot be instantaneous follows already from the fact that performing a measurement or passing a filter takes time, and was well-known very early in the discussion of foundations. For example, in his 1932 book, von Neumann writes:
John von Neumann said:
we have repeatedly shown that a measurement [...] must be instantaneous, i.e., must be carried through in so short a time that the change [...] is not yet noticeable
He makes clear that instantaneous is just an idealization for ''very short time''.
Of course, in non-relativistic QM you can invoke instantaneous processes as an "explanation" without being in conflict with causality, but you cannot do so within relativistic local microcausal QT, because that would be a contradiction.
So what? In relativistic local microcausal QT you can not even invoke Born's rule - since it implies positive probabilities of a system prepared locally for being observed one second later light years away. See Hegerfeldt's paper
Instantaneous spreading and Einstein causality in quantum theory,
Annalen der Physik 7 (1998), 716--725.
 

vanhees71

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Indeed, spontaneous emission is one of the (amazingly few) things you cannot make plausible in the semiclassical interpretation. Everything else you can, e.g., putting the hydrogen atom in a weak classical em. radiation field (e.g., a plane wave solution) and discuss the corresponding absorption and induced-emission "quantum jumps" via (first-order) time-dependent perturbation theory (usually in the dipole approximation, leading to the usual well-known selection rules for em. transitions). From this calculation you see very well that you get the literal quantum jump only in an idealizing approximation. Otherwise the occupation probabilities for the hydrogen eigenstates turn out to be smooth functions of time (oscillatory in this case).
 

Demystifier

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That's my very point!
So do you agree, as I argued in the post, that the minimal statistical ensemble interpretation is a theory in which additional variables are implicit?
 

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