On Thu, May 9, 2013 at 4:21 PM, meekerdb <[email protected]> wrote:
> On 5/9/2013 1:40 PM, Jason Resch wrote: > > > > > On Thu, May 9, 2013 at 3:14 PM, meekerdb <[email protected]> wrote: > >> On 5/9/2013 12:40 PM, Jason Resch wrote: >> >> >> >> >> On Thu, May 9, 2013 at 2:08 PM, meekerdb <[email protected]> wrote: >> >>> On 5/9/2013 11:28 AM, Jason Resch wrote: >>> >>> >>> >>> >>> On Thu, May 9, 2013 at 1:11 PM, meekerdb <[email protected]> wrote: >>> >>>> On 5/9/2013 10:02 AM, Jason Resch wrote: >>>> >>>> Von Neumann thought the extra baggage was required to make the model >>>> match our observations, but Everett later showed that step was >>>> unnecessary. The model (free of additional baggage) predicts the same >>>> observations as the model with it. >>>> >>>> >>>> He showed that IF the wave function separates into orthogonal >>>> components (an irreversible process) then FPI explains the observations. >>>> But the model says it never does that; it only approximates that, in >>>> certain bases. >>>> >>> >>> Could you explain this? I don't understand in what sense the >>> Schrodinger equation can only approximate itself? >>> >>> >>> If you include the observer and the system observed then when the >>> observer interacts with system in superposition the observers state becomes >>> a superposition >>> >> >> I follow you so far. To confirm we are on the same page, so you think >> observers are special in any physical way from any other "non observer" in >> a physical system? >> >> >>> in the same basis. The cross-terms in the superposition are not zero. >>> >> >> Do they need to be, what if they are not zero? How does a >> single-universe interpretation avoid this issue? >> >> >>> They can be shown to become approximately zero if you include >>> interaction with an environment that has a large number of degrees of >>> freedom and you trace over the environment variables. But that last step >>> isn't part of the Schrodinger equation, it's a separate assumption >>> comparable to Boltzmann's assumption of molecular chaos. >>> >> >> Earlier you said it can be shown, so how is it an assumption? Or do >> you mean it is an assumption that the environment has a large number of >> degrees of freedom? >> >> >> That and that the interaction is such that it diagonalizes in the >> variable(s) of interest. >> >> >> >> >>> >>> >>> >>> >>>> Decoherence theory tries to fill in the process by which this occurs >>>> give a statistical mechanics type account of irreversibility. >>>> >>> >>> It gives an account of the appearance of an "irreversible >>> wave-function collapse" without their having to be one. It is derived >>> entirely from the theory of QM and is not an extra postulate. >>> >>> >>> It depends on the choice of basis. In general there's other some basis >>> in which state is pure. Decoherence says the density of the subsystem is >>> approximately diagonal in a particular basis. This involves assumptions >>> about the environment and is not part of the wave function. >>> >>> >> It doesn't matter which/whose basis you use though, does it? >> >> >> It's not "whose" but "which". Most measurements are modeled as position >> measurements but you can invent ones that are measurements in momentum >> space too. But in general you can't create a measurement to determine the >> pure state which includes the environment. >> >> >> >>> >>> >>> >>>> But you could also take the epistemological interpretation of Peres >>>> and Fuchs instead of inventing other worlds just to save the determinism of >>>> an equation. >>>> >>> >>> The other worlds are a required element of the theory, unless you deny >>> the reality of superposition. I think Everett's thought experiment >>> explains the situation the best: >>> >>> Imagine a box with an observe in it who will be measuring the state of >>> a particle and writing the result in a notebook. This box is entirely >>> sealed off from the external world such that the internal result of the >>> experiment remains in a superposition until it is opened. Now a second, >>> external observer models the entire evolution of this box over time, >>> including before and after the observer inside measures the state of the >>> particle and records the result in a notebook. He determines the >>> superposition of all the possible handwritings of all the possible results >>> in the notebook. Is the internal observer not conscious in each of the >>> various superpositions resulting from the measurement? >>> >>> >>> Depends on what you mean by THE internal observer. There is a >>> superposition of states that represents the external observers theory of >>> the internal observer. >>> >> >> Okay, then from the view point of the external observers, shouldn't the >> various internal observers who remain in a super position, include >> observers each with a memories of recording one of the results in the log >> book, and in their brain? What happens to these memories (and presumably >> the experiences) when the external observer opens the room and collapses >> the superposition? Are we to believe all the memories and experiences that >> internal observer had are retroactively erased from existence and in fact, >> never happened at all? >> >> >> No, we believe the external observer needs to update the wave function >> he's using to describe the internal observer, based on his new information. >> >> > But what about what happened before the outside observer gets that new > information? Or are we just not allowed to talk or think about that? > > >> >> >> >>> >>> >>> >>> Epistemological interpretations seem to deny there is any fundamental >>> reality at all, aside from what we can see and learn, which to me seems >>> like a dead end in the search for truth. >>> >>> >>> Shifting the truth off to undetectable realms doesn't help much. >>> >> >> They are implied by the model of reality. >> >> >> They are implied by ONE model of reality. >> > > Yes, that is what I meant. > > >> >> >> Just like the galaxies beyond the cosmological horizon are implied by >> some models of inflation. Why contort a perfectly good and simple theory >> to make it match our (known) limited perceptive capacities? To me, single >> universe theories are as silly as any theory of inflation which said: "Once >> a galaxy crosses beyond our cosmological horizon, it ceases to exist, and >> any life forms that might have been in those galaxies cease to be." >> >> >> Except there are no galaxies that are observed to cross the Hubble >> sphere. >> > > Well according to inflation models there are galaxies that are outside > the Hubble sphere already (presumably some of them were not always outside > that sphere, because they were much closer and interacted leading to a very > uniform temperature throughout the universe). So whether or not we have > observed such a crossing is outside the point, it is in my opinion, an > equally indefensible position for the existence or non-existence of > something to hinge on one's ability to see it or interact with it. It's > like reverting to state of a someone who hasn't developed object permanence. > > > Galaxies aren't permanent. And according the concordance model they all > formed *after* inflation and so the only crossing of the Hubble sphere > would be from the outside to the inside. > Okay, lets use atoms then. It is a little harder to see atoms on the far sides of the Hubble volume, but it doesn't change the point I made. We make models of reality, and update, extend, or simplify those models as new evidence or reasoning permit. > > I'm perfectly happy to suppose that things exist that I can't interact > with, provided that's part of a theory that is superior in other ways. > Cool, we are in agreement on this. > But I don't see that saving determinism in an undetectable way makes for > a superior theory. > I agree, it is the fewer postulates that I think make QM (read literally) a superior theory. And unlike epistemological interpretations, it purports to model some reality that is really out there, independent of us or our observations. > > > > > >> >> >> >> >>> >>> >>> >>> >>> >>>> I like MWI and Bruno's FPI idea, but without some testable prediction >>>> (not retrodiction) I don't find them compelling. >>>> >>> >>> Why do you find compelling about the idea that all other >>> superpositions (except for one) vanish? >>> >>> >>> It comports with experiment. >>> >> >> What experiment even hints that other superpositions vanish? >> >> >> "Vanish" = no longer seen. >> >> > In this case, I was referring to the third definition: > http://dictionary.reference.com/browse/vanish?s=t which is what > single-universe theories hold happens to the other parts of the wave > function. That they are no longer seen because they no longer exist. MWI > explains why they are no longer scene, so why make the leap that they no > longer exist? > > > You keep assuming that because I don't vow allegiance to the MWI faith > that I reject it. I said I liked it, I'm just not compelled to accept it > so long has it has not empirical advantage. > Okay, I understand that position. However, I think right now we are in a state similar to that time when heliocentrism and geocentrism were debated, but before either was proven by observations of parallax. Neither theory has suffered a fatal blow, but there is a theory that is a little simpler. Would the creation of a working quantum computer that can factor thousand digit numbers (which not even an Earth-sized classical computer could) be a parallax moment for you? > > > > > >> >> >> >> >>> What do you find compelling about the idea that the unity of your >>> consciousness is an illusion. >>> >>> >> >> Is this the real source of your resistance to MWI, that you do not feel >> yourself split when your intuition suggests you should feel it? >> >> >> No. It's that it makes no testable predictions. >> > > > So single universe theories are right because they came first? > > If MWI had come first, would you reject the single universe theories of QM > because they make no testable predictions? > > >> It's just metaphysics to satisfy a demand for determinism - unless it can >> predict something. >> >> > > Again, I repeat this is not about determinism at all, it is about > reading the theory for what it is, a model of reality itself, and not > adding additional assumptions or postulates which are in no way needed for > the model to be consistent with our observations. > > > But whether it is really consistent, even consistent with the appearance > of the classical world, is not clear. The decoherence program may > eventually show it to be, but for now there are still problems. It may be > that the solution requires a theory of consciousness like Bruno's. > > Yes that could be. > > > (All this ignores any preference one may have for determinism, locality, > linearity, reversibility, which are features of nearly every other known > physical principle) > > > >> >> >> Don't worry, you don't need to condemn your copies to a superposition >> with 0 amplitude to explain why you (in this branch), do not have access to >> the memories/experiences of the other yous (in other branches). >> >> This is the same error presentism makes: believing we must make all >> other points in time non-real to explain why we feel ourselves to be in >> this single point in time. >> >> So to answer your question, what I find compelling is not contorting a >> theory to solve imagined problems. >> >> >> I think of non-determinism as an imagined problem. >> > > So be it. I haven't once in this discussion said it is a problem or is > not a problem. You, however, have not provided any justification for why > we should believe things we cannot see must not exist. > > > Nor have you shown shown why we should believe Everett's multiple worlds > must exist. But as a rule-of-thumb it is better to tentatively assume > things we cannot see don't exist. > I don't think MWI must be true, but I have offered reasons for why I think Everett's model is preferred. I prefer it for the same reason one might prefer heliocentrism (even before any conclusive experiment is performed): it is more elegant. Jason -- 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 http://groups.google.com/group/everything-list?hl=en. 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