Thanks Shan for this question. If the measurement events are spacelike separated, then according to relativity, there is no invariant time order for the two events. That is, it’s not possible to consider them simultaneous in any invariant sense–that would pick out a preferred frame, and relativity doesn’t allow that. For an observer heading…[Read more]

Yes, I think the definition of ‘collapse’–what collapse means physically–does matter for the issue of concern to you. In this latest post you seem to be talking about a single quantum, not an entangled state, right? Bell’s inequality concerns correlations between entangled particles.
In any case, for this single-particle measurement, the…[Read more]

Again, collapse in TI for any detected quantum is associated with both emission and absorption of that quantum–two events for each detected quantum, not one. This is an important difference bewteen TI and other collapse theories, which view collapse as singling out a particular time index. That is not the case in TI. In TI, collapse establishes…[Read more]

Jonathan, I have to differ with your initial claim that “Every interpretation of quantum mechanics posits, as axioms, a set of rigid idealizations about measurement.” This not the case, since the transactional interpretation does not do so. Measurement is neither idealized nor an axiom in TI (nor in RTI, the relativistic version.) In TI,…[Read more]

Hi Shan:
I’ve started looking at this interesting paper, but I do have to note that there is an exception to the general observation that ‘Collapse theories single out a preferred frame’. The Transactional Interpretation is a collapse theory, but it does not single out a preferred frame. This is made explicit in its relativistic development, RTI,…[Read more]

Thanks Richard, let me address your comment that:

… if there were no true magnitude claims then an application of the Born rule would have nothing to which to assign probabilities!

The above statement/position depends on the notion of ‘magnitude claim’. That’s a linguistic entity, and I think we earlier agreed that QM doesn’t demand or depend…[Read more]

Mark: of course, I’ve contended and continue to contend that the disease infecting conventional approaches to QM is that nobody can define ‘measurement’. This leaves adherents of these traditional approaches to simply help themselves to measurement results. In particular, I would have to respectfully differ with Richard’s comment:

The argument…

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Thanks very much Richard.
Of course, in the transactional picture, once photons are detected/actualized (as is necessary to yield a current), collapse has occurred, and conserved quantities (such as angular momentum, spin, etc) have been transferred. (Photons are the mediator of em processes such as the creation of electron current; for details,…[Read more]

Thanks very much, Richard.
Regarding the interpretation of probability, it seems that this is still an open question. I don’t think the Born probability is restricted to being about semantic objects such as claims. It can be directly about a system’s actualized properties (at least it certainly can in TI).
But in any case: I recognize that…[Read more]

Richard, do I understand correctly that in your proposed approach, measurement outcomes have no relation to values of observables for the system? My question arises from your statement:

In particular, it makes no assumption concerning the actual spin values of the measured particles, either before or after the spin measurements. It assumes only…

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Thanks, Richard for this clarification.
Of course, I think your analysis can also perfectly well apply to an ontic role for the quantum state.
Under an epistemic view of the quantum state, then it seems to me that if one posits that measurements really do have definite outcomes, then an implicit hidden variable view must be lurking in the…[Read more]

This is an interesting situation: assessments of the bearing and validity of the FR proof greatly depend on what quantum theory itself is taken to be. For example, Editor has referred to two different forms of QT:
(1) QT with collapse postulate — call it “QTCP”
(2) QT without collapse postulate — call it “QTNCP”
…and has noted, based on…[Read more]

I would just comment here that Brukner’s formulation of the measurement problem presupposes an epistemic interpretation of the quantum state relative to a particular observer. So his analysis and conclusions do not apply to cases in which the quantum state ontologically refers. In particular, he concludes that facts are necessarily…[Read more]

Dear Editor: Should I start a new topic to address the measurement problem, which is what is being illustrated by the Wigner’s Friends scenario? In particular, we don’t encounter a Wigner’s Friend dilemma in the first place if we have a means of delineating, in physical terms, what constitutes ‘measurement’ (where that is described by von…[Read more]