On Monday, May 21, 2018 at 12:22:24 AM UTC, Brent wrote: > > > > On 5/20/2018 4:56 PM, [email protected] <javascript:> 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 > > 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 > > 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.
