> On 16 Aug 2018, at 13:12, Bruce Kellett <bhkell...@optusnet.com.au> wrote: > > From: Bruno Marchal <marc...@ulb.ac.be <mailto:marc...@ulb.ac.be>> >>> On 15 Aug 2018, at 13:33, Bruce Kellett <bhkell...@optusnet.com.au >>> <mailto:bhkell...@optusnet.com.au>> wrote: >>> >>> Do you really no know how to pick out a typical component from an ensemble? >> >> >> I cannot when the elements cannot be distinguished. > > The fact that they cannot be distinguished is what makes picking a typical > element so easy, and so useful. > >> Alice cannot do that, but each Bob and Alice picks their counterparts by >> doing their measurements, but that take some times. > > That is not what I was talking about. > >>> 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. > > This is not a matter of many-worlds vs Copenhagen. > >> You seem to reintroduce implicitly some collapse in the picture. > > Why do you think that picking a typical branch in a superposition involves > some collapse? That is daft. > >> 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*. > > No, there are only two possible values for the direction in which the > measurement is made.
That is what I said. You lost me. I am not even sure what we are discussing, unless you come back with John Clark’s idea that physical FTL *influence* still exist to account for the violation of Bell’s inequality. > There are no "possible directions of the spin" prior to the measurement. ? > You are reverting to a hidden variable account again. Absolutely not. > These "possible directions of the spin" would be hidden variables in any > mathematical account of such a theory, and we eschew hidden variables. It would be if the spin was decided in advance for each direction, but Alice is in the two corresponding world at once, and this for all direction of spins. If not, the singlet state would be, in the MW theory, base dependent, which it is not. > >> 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. > > You are using a very strange notion of a "world”. I suspect we disagree on what is a world. You lost me completely on your interpretation of a superposition or any quantum state in the MW theory (that in the wave when we accept the idea that it never collapses). > As I have frequently explained, a 'world' arises only when decoherence Which is only entanglement in the MW theory. > has caused the elements of a superposition to become effectively orthogonal > -- disjoint FAPP. And FAPP is sufficient because worlds are defined for > practical purposes. ? (We need only stable local neighbourhoods). Worlds is a typical metaphysical notion. > This does not happen in either the singlet case, or the case of electron > orbitals. So if there is no infinity of worlds in either case: there is not > an infinite number of copies of Alice measuring the singlet state. Then I don’t know how you apply QM to Alice when looking where is an electron. > >> Are you OK with this? I try to figure out what is your interpretation of the >> SWE. > > No, I am not OK with your notion of a 'world'. It makes no sense, and it > serves no purpose to confuse this peculiar notion with the well-defined > notion of disjoint components of the wave function. You lost me completely. What you say is hard to relate to Everett or any account of the wave without collapse. I think you just deny the MW. If Alice look at the position of an electron, she will find herself in all worlds with different position for that electron. The worlds proportion are enacted by the density of presence of the electron in the orbital. That follows from from elementary QM without collapse, by the linearity of the tensor products and the linearity of the Schroedinger wave evolution. 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 everything-list+unsubscr...@googlegroups.com > <mailto:everything-list+unsubscr...@googlegroups.com>. > To post to this group, send email to everything-list@googlegroups.com > <mailto:everything-list@googlegroups.com>. > 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 everything-list+unsubscr...@googlegroups.com. To post to this group, send email to everything-list@googlegroups.com. Visit this group at https://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
