On Monday, May 21, 2018 at 8:12:11 PM UTC, Brent wrote: > > > > On 5/21/2018 11:21 AM, [email protected] <javascript:> wrote: > > > > On Monday, May 21, 2018 at 5:28:38 PM UTC, Brent wrote: >> >> >> >> On 5/20/2018 6:25 PM, [email protected] 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? > > > They are inaccessible to the people of any one world of the MWI. >
There you go again! Listen; I want to determine whether quantum measurements are reversible, so I don't accept arguments based on interpretations neither of us believe in. Can you do better without appealing to the projection operator? AG > > 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. > > > OK, then you've qualified it to mean nomologically irreversible...but > still logically (mathematically) reversible. > I consulted several dictionaries and still don't understand the word. Above my pay grade I suppose. As for mathematically reversible, are we playing the movie backward again? I am interested in the physical reality, not some equation that tells me a measurement is reversible if it isn't! 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.
