> On 21 Aug 2018, at 22:24, Brent Meeker <[email protected]> wrote: > > > > On 8/21/2018 6:51 AM, Bruno Marchal wrote: >> >>> On 21 Aug 2018, at 14:53, Bruce Kellett <[email protected] >>> <mailto:[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). > > This assumes that Alice has used a measuring instrument whose interaction is > spherically symmetric. It is because her instrument has an infinite (or at > least very big) number of possible results that there are an infinity (or > many) Alice's. > >> 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. > > But direction is chosen via her thought processes which are effectively > classical. Her wf is not rotationaly symmetric. It could be arranged that > some quantum random number generator is used to set the detector angle to X. > In that case the multiverse would split into many different branches when the > qrng result decohered and output X. But this event would still leave Alice > and Bob spacelike separate in the world where the qrng output X. There will > be many branches corresponding to the many possible values of X. But in each > branch the change of the wf when Alice measures the spin along X will be a > non-local splitting into "up-X" or "down-X". At least that's conventional > QM.
? Conventional Everett QM? That discussion is fruitful, we see clearly where we disagree. It is on how to interpret the many-worlds view of the tensor products, which are admittedly weird. I think that any interpretation which threats the covariance of the physical reality is doubtful. What can happen is that the dream/computations do not cohere enough to get any definite global physical reality. But I think it is premature to say this, both empirically and theoretically. Bruno > > Brent > >> 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] >> <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] > <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. 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