Reply to Aurelien: No, RTI has emphatically nothing to do with Bohr or the Copenhagen interpretation, which I criticize and reject here:https://arxiv.org/abs/1601.07545
If you read my publications, you will find that I assign objective physical reality to quantum states and the advanced states. You seem to be implicitly assuming that for something…[Read more]

To Shan: That is correct. The collapse occurs with respect to projection operators (outer products), not with respect to kets. That is, from absorber response to each component we get two weighted projection operators:|Psi1><Psi1| and |Psi2><Psi2|, where each is weighted by the Born Rule based on the prepared state. So if the prepared state was…[Read more]

Dear Aurelien, RTI does not require any preferred foliation; it does not require any future boundary condition. It is not a hidden variable approach nor does it rely on a notion that measurement outcomes are ‘already there’ in the future–i.e. it is not a block world ontology. I understand that the original TI may have seemed to imply that, but…[Read more]

Thanks Shan. In RTI the quantum state |Psi> is fully ontic. But the advanced state <Psi| is also fully ontic, so RTI is a different animal from the usual ‘quantum interpretation.’ This is why it is not subject to the dilemma you pose. It has real ontic collapse, but the collapse is not with respect to just a forward-propagating quantum state. In…[Read more]

Thanks Aurelien, I am indeed aware of the Sutherland model and you are correct that it is covariant, except perhaps for the final boundary condition which has to be defined in a particular frame (but it’s a matter of debate as to whether that ‘really’ fixes a preferred frame). Other than the final B.C., the model preserves full Lorentz covariance.…[Read more]

I’m afraid this is not the correct conclusion. While RTI is certainly not the usual ad hoc collapse theory, it certainly is a non-unitary objective reduction theory (see below). So it cannot be subject to your argument concerning unitary-only theories. There is real dynamical reduction in TI–it just does not take the form that you’ve assumed…[Read more]

But the existence of the observed correlation does not compel the idea that there is some sort of collapse signal that ‘travels faster than light.’ You might be supposing that such a ‘collapse signal’ is needed to enforce the correlation, but that is not the case in TI, where the correlation is enforced through the combination of the quantum state…[Read more]

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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