On Monday, May 21, 2018 at 5:28:38 PM UTC, Brent wrote: > > > > On 5/20/2018 6:25 PM, [email protected] <javascript:> wrote: > > > > On Monday, May 21, 2018 at 12:22:24 AM UTC, Brent wrote: >> >> >> >> On 5/20/2018 4:56 PM, [email protected] wrote: >> >> >> >> On Sunday, May 20, 2018 at 10:35:26 PM UTC, Brent wrote: >>> >>> >>> >>> On 5/20/2018 2:54 PM, [email protected] wrote: >>> >>> >>> >>> On Sunday, May 20, 2018 at 9:13:42 PM UTC, Brent wrote: >>>> >>>> >>>> >>>> On 5/20/2018 1:44 PM, [email protected] wrote: >>>> >>>> >>>> >>>> On Sunday, May 20, 2018 at 7:29:42 PM UTC, Brent wrote: >>>>> >>>>> >>>>> >>>>> On 5/20/2018 3:47 AM, [email protected] wrote: >>>>> >>>>> >>>>> >>>>> On Sunday, May 20, 2018 at 6:52:41 AM UTC, Brent wrote: >>>>>> >>>>>> >>>>>> >>>>>> On 5/19/2018 8:19 PM, [email protected] wrote: >>>>>> >>>>>> >>>>>> >>>>>> On Saturday, May 19, 2018 at 3:59:03 PM UTC, Brent wrote: >>>>>>> >>>>>>> >>>>>>> >>>>>>> On 5/18/2018 10:53 PM, [email protected] wrote: >>>>>>> >>>>>>> >>>>>>> >>>>>>> On Saturday, May 19, 2018 at 5:29:33 AM UTC, Brent wrote: >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> On 5/18/2018 10:14 PM, [email protected] wrote: >>>>>>>> >>>>>>>> >>>>>>>> *So why don't you draw the obvious inference? If those other worlds >>>>>>>> don't exist -- which if I can read English has been your passionate >>>>>>>> position all along -- then quantum measurements in this world, the >>>>>>>> only >>>>>>>> world, are statistical and hence NOT reversible in principle. AG* >>>>>>>> >>>>>>>> >>>>>>>>> but it is different in each branch of the wave function, so >>>>>>>>> reversing this branch does nothing for the others, and does not >>>>>>>>> restore the >>>>>>>>> original superposition. Thus the process is irreversible in principle >>>>>>>>> (nomologically irreversible -- to reverse violates the laws of >>>>>>>>> physics). >>>>>>>>> >>>>>>>> >>>>>>>> *But if those other worlds don't exist, it makes no sense whatever >>>>>>>> to rely on them to establish irreversible in principle in this world >>>>>>>> (as >>>>>>>> distinguished from statistically irreversible or irreversible FAPP). >>>>>>>> It >>>>>>>> seems you want to have it both ways; that many worlds really don't >>>>>>>> exist. >>>>>>>> but quantum measurements in this world are irreversible in principle >>>>>>>> due >>>>>>>> the existence of many worlds. AG* >>>>>>>> >>>>>>>> >>>>>>>> You don't handle uncertainty well, do you. >>>>>>>> >>>>>>>> Brent >>>>>>>> >>>>>>> >>>>>>> You know, it's not a perfect analogy, but I don't believe that when >>>>>>> I pull the one arm bandit with 64 million possible outcomes, that 64 >>>>>>> million (minus one) worlds are created, each with an identical copy of >>>>>>> me, >>>>>>> getting those other outcomes. What do you believe? AG >>>>>>> >>>>>>> >>>>>>> I believe I'll wait for a better theory. One that includes gravity >>>>>>> and spacetime and consciousness. >>>>>>> >>>>>>> Brent >>>>>>> >>>>>> >>>>>> I see. But you seem too ready to defend the MWI when it appears to >>>>>> imply irreversible in principle. Or do you accept Bruce's claim that the >>>>>> projection operator implies irreversible in principle? AG >>>>>> >>>>>> >>>>>> Either of them implies irreversiblity. Whether it is "in principle" >>>>>> depends on what principle you invoke, mathematics, practice, ...? MWI >>>>>> puts >>>>>> information in orthogonal subspaces where we exist in copies such that >>>>>> each >>>>>> copy can act only in one subspace and hence cannot put together the >>>>>> information from other subspaces. A projection operator is just a >>>>>> mathematical model of this confinement to one subspace. >>>>>> >>>>>> Brent >>>>>> >>>>> >>>>> Please; no evasive games. We can forget about the MWI, given its >>>>> absurdity. Does, or does not the projection operator imply >>>>> irreversibility >>>>> in principle as Bruce claims? AG >>>>> >>>>> >>>>> Sure, a projection operator throws away information so its action is >>>>> irreversible. If I project a star onto the celestial sphere I preserve >>>>> its >>>>> longitude and latitude, but it doesn't show how far away it is. That's >>>>> why >>>>> the MWI advocates say projection conflicts with all the rest of >>>>> fundamental >>>>> physics which is described by evolution that is at least reversible in >>>>> the >>>>> mathematical sense. >>>>> >>>>> Brent >>>>> >>>> >>>> But how do you know that the projection operator represents an actual >>>> physical process? It could be just a bookkeeping device to describe the >>>> fact that when many possible outcomes are possible, we get a particular >>>> outcome. >>>> >>>> >>>> Exactly. The quantum Bayesian take this view >>>> >>> >>> How does "Baysian" fit into this picture? Can't one interpret the SWE as >>> a representation of what we know about a system, without being a Baysian? AG >>> >>> >>>> and consider Schroedinger's equation also as a personal book keeping >>>> device of what one knows about a system and then the Born rule and >>>> projection operators fit neatly into the scheme of updating one's personal >>>> knowledge. >>>> >>> >>> I would delete "personal" from your comment. We're referring to the >>> knowledge of any observer. AG >>> >>>> >>>> ISTM, that to argue for "irreversible in principle", it is insufficient >>>> to appeal solely to the properties of the projection operator. AG >>>> >>>> Exactly what led to Everett, MWI, and decoherence theory. But at the >>>> price of having multiple, orthogonal "worlds" to explain the appearance of >>>> randomness. Of course some people hate randomness and are quite happy to >>>> have multiple worlds instead. >>>> >>> >>> Looks like I am in the decoherence camp; namely, that when a quantum >>> measurement occurs, entanglements with reservoir states somehow suppresses >>> all outcomes but one >>> >>> >>> But that "somehow" is the magic of the Copenhagen interpretation. >>> Decoherence is the process of making subspaces (worlds) orthogonal, but it >>> doesn't choose one and "suppress" (vanish?) the others. The all continue >>> to exist and to be orthogonal,. >>> >> >> There's no magic; just an unknown process that allows one result and not >> others. >> >> >> Right. And there have been some serious proposals for that process, like >> Penrose's gravitational metric difference. >> >> That the other subspaces continue to exist and are orthogonal and >> inaccessible, is the result of imposing the projection operator. >> >> >> No. The SE causes them to evolve into orthogonal subspaces, no >> projection operator required. That's what Everett showed to be a >> consequence of treating the instruments and the observer all as quantum >> systems. >> > > How can the SE do that without a measurement? IIUC, the probability > amplitudes just keep evolving in time absent a measurement. No measurement; > no orthogonal subspaces. I think they come about due to the projection > operator, a housekeeping device. AG > > > That's the problem decoherence solved. It doesn't have to be a > "measurement" in the sense of someone seeing the result. That's the lesson > of the buckyball two-slit experiment. >
I'm OK with getting rid of the projection operator. Are you now claiming information is lost or inaccessible in these orthogonal subspaces and therefore quantum measurements cannot be reversed? I'm confused as to where we are in this discussion. AG > > >> IOW, I conjecture that the founders of quantum theory made it an >> irreversible in principle theory without sufficient reasons. AG >> >> >> Well, they thought the fact that they observed their lab notes didn't >> reverse themselves was a sufficient reason. >> > > The lab notes showed they got a measurement; a single measurement. So they > added the projection operator to account for that. Nothing firm about > irreversible in principle AFAICT. AG > > > Again you casually use the pharse "in principle" with saying what > principle. > I don't have to since "irreversible in principle" means there is no physical process which allows the measurement to be reversed. AG > > Brent > -- 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.
