> On 21 Aug 2018, at 14:53, Bruce Kellett <[email protected]> wrote: > > From: Bruno Marchal <[email protected] <mailto:[email protected]>> >>> On 21 Aug 2018, at 02:20, Bruce Kellett <[email protected] >>> <mailto:[email protected]>> wrote: >>> >>> From: Bruno Marchal <[email protected] <mailto:[email protected]>> >>>>> On 20 Aug 2018, at 13:18, Bruce Kellett <[email protected] >>>>> <mailto:[email protected]>> wrote: >>>>> >>>>> >>>>> You didn't respond to my earlier post in which I discussed the symmetry >>>>> breaking occasioned by Alice's measurement interaction with the singlet >>>>> state. I copy the relevant parts of my earlier post here: >>>>> >>>>> "The fact that Alice's interaction with the state is unitary and can be >>>>> reversed does not mean that the original symmetry still exists in some >>>>> sense. If I place a large weight at some point on the circumference of a >>>>> bicycle wheel, the rotational symmetry of that wheel is lost. The fact >>>>> that I can reverse the process by removing the imposed weight does not >>>>> mean that the altered wheel is still rotationally symmetric in some wider >>>>> view.” >>>> >>>> OK, but when the heavy object is removed, at that moment, the symmetry is >>>> back. Then, when Alice makes the measurement, the symmetry is lost from >>>> her point of view, but the general symmetry of the state has not changed. >>>> It is only not retrievable by Alice (unless quantum erasure, amnesia, >>>> etc.). >>> >>> Bruno, you have not made the least effort to understand the point I made >>> above, >> >> Stop speculating on people. > > I am merely responding to what you wrote. No speculation involved.
How do you know I did not make some effort. Maybe you imagine that I am clever or something. You might need to develop some sense of pedagogy. > >>> or to respond to it intelligently. >> >> Sop making judgement. > > There has been no intelligent response. No judgement involved. That is a contradiction. > >>> It is difficult to believe that you are actually discussing this in good >>> faith. You just keep repeating your own misunderstandings of the situation. >> >> This is discussed since the beginning of QM. Stop talking like if only you >> understand Everett. > > Well, it does not appear as though you do either. You keep adding in > infinities of observers that are not part of Everett's formulation of QM. There are two sort of infinity here. One which I hope you agree with, like when Alice measure the position of an electron prepared in the state of lowest energy level of an electron around a proton. The electron state is a superposition of all position possible in the corresponding orbital. After measurement she is entangled with that electron, and we have an infinity of Alice. OK? (I assume of course some classical QM; that might need some correction when GR is used). The other sort of infinity, the one which I think you disagree with, is typical for the superposition of tensor products, like the singlet state ud - du. Before measurement Alice has the same probability of finding u, or d for any measurement she can do in any direction. Both Alice and Bob are maximally ignorant of their possible measurement results. The MW on this, or a MW way to interpret this, to keep the rotational symmetry, is that we have an infinity of couples Alice+Bob, with each couple being correlated. If not, some implicit assumption is made on u and d, like it is a preferred base. And yes, I do assume locality, if only to illustrate that the MW does not force the presence of FTL influence (without transfert of information, which actually would require a third person indeterminacy in Nature, which I doubt). It is just a consequence of ud-du = u’d’-d’u’, and the fact that this implies maximal ignorance of Alice (and Bob) whatever spin-direction is chosen. After the choice of Alice, and her measurement, neither Alice and Bob will be able to access a different world. All Alice and Bob will have to interpret the state like if it was s simple (two terms) superposition. It is like suppressing the global phase of the state. > >>> The measurement that Alice makes destroys the symmetry. That is all there >>> is to it. There is not some wider symmetry that is preserved. >> >> That is Bohr theory. Not Everett. A measurement does not change anything in >> the big picture. It collapses wave and destroys symmetries only in the >> relative first person mind associated to bodies doing the experience. > > It is not Bohr's theory, it is quantum mechanics. You appear to believe that > symmetry cannot be destroyed, The symmetry is destroyed from the perspective of the one doing the experiment. But it is extended to the couple Alice + the singlet state, although “rational symmetry” might be have its usual definition slightly enlarged. > even though I have given clear examples where this happens. It was using some collapse. It seems to me. > The symmetry is destroyed totally, not just in the mind of the experimenter. > If the symmetry is still preserved in some bigger picture, it is up to you to > prove this. But you have not been able to do so. It is just an assertion on > your part. And that assertion happens to be false. You seem to believe that a measurement has to change something in the physical reality (besides the brain of the observer). But that does not happen in the MW. Measurement is only self-entanglement. It broke the symmetry of the singlet state, but enlarge it on the system Aice+singlet state. Bruno > > What you have to do is to work through the application of the Schrödinger > equation for this situation, without invoking any collapse, and demonstrate > that the symmetry is still present in the total wave function. I contend that > you will not be able to do this, because the interaction with the singlet > state destroys the rotational symmetry. This is really a trivial observation > since the Stern-Gerlach magnet itself is not rotationally symmetric. > > Bruce > > -- > You received this message because you are subscribed to the Google Groups > "Everything List" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected] > <mailto:[email protected]>. > To post to this group, send email to [email protected] > <mailto:[email protected]>. > Visit this group at https://groups.google.com/group/everything-list > <https://groups.google.com/group/everything-list>. > For more options, visit https://groups.google.com/d/optout > <https://groups.google.com/d/optout>. -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. 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