> On 15 Aug 2018, at 13:33, Bruce Kellett <[email protected]> wrote: > > From: Bruno Marchal <[email protected] <mailto:[email protected]>> >>> On 15 Aug 2018, at 01:48, Bruce Kellett <[email protected] >>> <mailto:[email protected]>> wrote: >>> >>> From: Bruno Marchal <[email protected] <mailto:[email protected]>> >>>>> On 14 Aug 2018, at 04:30, Bruce Kellett <[email protected] >>>>> <mailto:[email protected]>> wrote: >>>>> >>>>>> If they are space separated, I am not sure I can make sense of being in >>>>>> the same branch. >>>>> >>>>> You appear to be referring to the presence of quantum fluctuations >>>>> continually splitting the classical Alice and Bob into multiple copies -- >>>>> the point that Jason has made. >>>> >>>> That points is correct, but I was alluding to the infinity of Bob and >>>> Alice couples associated with the singlet state. That is needed to tackle >>>> the case where Alice and Bob makes non orthogonal measurements. >>> >>> I was trying to make sense of the suggestion of many Alices and Bobs before >>> any measurement. That can easily be implemented by having Alice select her >>> measurement angle according to the time of some radioactive decay. Since an >>> infinity of decay times is possible, we get a superposition of an infinite >>> number of copies of Alice. >> >> OK. But we have this in our context too. >> >>> But this makes not difference to the basic argument -- one just picks out a >>> typical Alice. >> >> How? > > Do you really no know how to pick out a typical component from an ensemble?
I cannot when the elements cannot be distinguished. Alice cannot do that, but each Bob and Alice picks their counterparts by doing their measurements, but that take some times. > >>> You are wrong when you claim that an infinity of couples are required to >>> make sense of measurements made at arbitrary angles. >> >> Why? > > Because that is not how angular momentum operators in quantum mechanics work. > >>> The singlet state is rotationally symmetric, >> >> That’s why. > > That's why what? That is why a singlet state describe a collection of situations withAlice’s particles spin well defined in all directions (and the opposite for Bob). But none know which one. > >>> and can be expressed in any base. But this does not mean that there >>> actually exists a copy of the observer for each of the potential bases. >>> That idea makes no sense at all; it is not part of quantum mechanics in any >>> possible formulation. >> >> ? >> >> That would contradict the complementary principle. A well localised particle >> is a particle having almost all possible momenta in many different histories. > > For fuck's sake, Bruno. Do you understand nothing of elementary quantum > mechanics? No comment. > The angular momentum operators do not commute, sure, so that if one has a > precise measurement in one direction, one has no knowledge of the projection > in an orthogonal direction. But the possible values of any such operator on > the spin-1/2 state are +1 or -1 (in units of hbar/2). So there is no infinity > as there is in the case of the complementarity of position and momentum > operators! No problem with this, but Alice can choose to measure that spin in any direction. > > Besides, it is possible to have exact values for both the total angular > momentum operator (L^2) and any particular component, say L_z if we are > measuring in that direction, and that is all we require here. See the > Wikipedia article: > > https://en.wikipedia.org/wiki/Angular_momentum_operator#Uncertainty_principle > <https://en.wikipedia.org/wiki/Angular_momentum_operator#Uncertainty_principle> > > >>>> The singlet state does not single out one base, despite the notation. It >>>> describes an infinite of Alice and Bob right at the start. >>> >>> Sure, the singlet state does not single out one base. But that does not >>> mean that it describes an infinity of observers. Just because you can >>> measure at any angle does not mean that there is actually an infinity of >>> observers making all those possible measurements. That notion is just crazy. >> >> ? >> >> It is just what the wave described literally. > > No, it is not. Look up some reference on the application of the uncertainty > principle to angular momentum operators. (Such as the Wikipedia article > above.) I do not see any problem between what I said and that wiki pages, which is rather neutral on the interpretations. They do not provide the “many-worlds” view on this, and some links there suggests they use the Copenhagen formulation. You seem to reintroduce implicitly some collapse in the picture. That’s my feeling, as this is not clear. When measuring a spin: there are two possible values *for all possible direction of the spin*. That makes infinitely many worlds. Same for an electronic orbital. There are as many world that the possible position of the electron in the orbitals. Are you OK with this? I try to figure out what is your interpretation of the SWE. Bruno > > 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]. Visit this group at https://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
