Dear Ruth, I would like to add a comment concerning the role of preferred frames in a quantum ontology and in connection with retrocausality. It is indeed possible to develope Bohmian like model without preferred frames. There is one recent approach by Sutherland but I also recently proposed a different one…[Read more]

Hi Jeff,

On p. 7 you write, “This intrinsic randomness allows new sorts of nonlocal probabilistic correlations for ‘entangled’ quantum states of separated systems.” We offer an explanation (couched in spacetime) of this fact in our post, Mysteries of QM and SR Share a Common Origin: No Preferred Reference Frame.

For example, in the simple…[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]

Ok, Ruth. I see. Then RTI is not really the usual collapse theory such as the GRW model for one-vector. So, in RTI, there is no real dynamical collapse of the wave function. Then my analysis of collapse theories does not apply to RTI.

Now I think my analysis of unitary quantum theories will apply to RTI. See my paper section about the…[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]

So, you also agree that “in the second scenario, in which Bob’s measurement precedes (in the lab frame) all of Alice’s measurements”, “Since Alice cannot know Bob’s outcome before that event enters her back light cone, all she can predict with certainty at points on her worldline before making those measurements is that, whatever they are, they…[Read more]

In my previous reply I said that when the Born Rule is applied from an agent situation indexed to a spacetime point p on Bob’s worldline that is timelike later than Bob’s outcome (such as point 3 in Figure 1) it yields chance 0 or 1 for each of Alice’s measurement outcomes in regions a – e. So from that agent situation, each of Alice’s outcomes is…[Read more]

Thanks for your clarification, Richard!

But I cannot agree with you. I think the Born Rule must be applied at a time, while this would not necessarily introduce a preferred frame in relativity as some people think, although my new argument says the opposite.

The reason is that if the Born Rule is not applied at a time for a joint measurement of…[Read more]

You said “no way for Alice to check that when she detected, say particle #25, that Bob did not get that particle, because in order to do that, the two would have to exchange classical information faster than light.”

Yes, you are correct. But this is not necessary to verify the anti-correlation. They just need to record the results, and then…[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]

The Born Rule should always be applied not at a time (that would already introduce a preferred frame in relativity) but from what I have elsewhere called an agent situation—a physically specified situation that may or may not actually be occupied by an agent. In this Gedankenexperiment we may take an agent situation to be adequately specified by…[Read more]

Thanks, Ruth! I will need to undertand your idea more deeply.

Here is what I thought. Suppose ALice measures the particle in box 1, and then Bob meqasures the particle in box 2. These two measurements are spacelike and almost simutaneous. Then, when Alice have dectected the particle in box 1, the superpostion should collapse also in the remote…[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]

Hi Richard,

Thanks for your comments! In your paper, you said:

“In the second scenario (i.e. Bob precedes Alice) Gao argued that the Born rules yields probability 1 for the sequence of outcomes of Alice’s repeated z-spin measurements in which every outcome is the opposite of Bob’s single outcome of a measurement at point 3, and probability 0 t…[Read more]

I think the issue is not really related to the detials. Consider a particle is in a superposition of two well-separated boxes. When one measures the particle in one box, then the whole superposition collapses to the state in one of the two boxes. Now if the collapses of the superposition in the two boxes are not space-like seperated in any frame,…[Read more]