> On 9 Oct 2019, at 11:17, Philip Thrift <cloudver...@gmail.com> wrote: > > > > On Tuesday, October 8, 2019 at 6:24:28 PM UTC-5, Brent wrote: > > > On 10/8/2019 2:59 PM, Philip Thrift wrote: >> >> >> On Tuesday, October 8, 2019 at 2:40:33 PM UTC-5, Brent wrote: >> >> That MWI entails other, unobservable "worlds" is neither a bug or a feature, >> it's just one answer to the measurement problem. If you have a better >> answer, feel free to state it. >> >> >> Brent >> >> >> >> MWI, according to Sabine Hossenfelder, is not an answer - in the final >> analysis - to the measurement problem >> >> http://backreaction.blogspot.com/2019/09/the-trouble-with-many-worlds.html >> <http://backreaction.blogspot.com/2019/09/the-trouble-with-many-worlds.html> >> >> >> The many world interpretation, now, supposedly does away with the problem of >> the quantum measurement and it does this by just saying there isn’t such a >> thing as wavefunction collapse. Instead, many worlds people say, every time >> you make a measurement, the universe splits into several parallel worlds, >> one for each possible measurement outcome. This universe splitting is also >> sometimes called branching. >> >> Some people have a problem with the branching because it’s not clear just >> exactly when or where it should take place, but I do not think this is a >> serious problem, it’s just a matter of definition. No, the real problem is >> that after throwing out the measurement postulate, the many worlds >> interpretation needs another assumption, that brings the measurement problem >> back. >> >> The reason is this. In the many worlds interpretation, if you set up a >> detector for a measurement, then the detector will also split into several >> universes. Therefore, if you just ask “what will the detector measure”, then >> the answer is “The detector will measure anything that’s possible with >> probability 1.” >> >> This, of course, is not what we observe. We observe only one measurement >> outcome. > > The implication is that the above two sentences are contrasting. But nobody > asks "what will the detector measure". The question asked by the > experimenter is "which measurement outcome will the detector detect", which > is perfectly consistent with "we observe only one measurement outcome" > >> The many worlds people explain this as follows. Of course you are not >> supposed to calculate the probability for each branch of the detector. >> Because when we say detector, we don’t mean all detector branches together. >> You should only evaluate the probability relative to the detector in one >> specific branch at a time. > > I can't even parse that. You are supposed to calculate the probability of > each possible measurement outcome and those characterize the branch. It is > NOT calculating "each branch of the detector" unless you are defining those > "branches" by what the measurement outcome is. > >> >> That sounds reasonable. Indeed, it is reasonable. It is just as reasonable >> as the measurement postulate. In fact, it is logically entirely equivalent >> to the measurement postulate. > > It's not clear here what "logically" equivalent means. It is instrumentally > equivalent...which is why it's an interpretation and not a different theory > (as GRW is). It's different from the measurement postulate in that the > measurement postulate says the wave function instantaneously changes to match > the observed measured value. MWI says those other measured values obtain in > other orthogonal subspaces of the Hilbert space and you are only observing > one. Those are not "logically" the same. > >> The measurement postulate says: Update probability at measurement to 100%. >> The detector definition in many worlds says: The “Detector” is by definition >> only the thing in one branch. > > What does "only the thing in one branch mean". In MWI there are projections > of the detector in subspaces which differ only by the value detected. > >> Now evaluate probabilities relative to this, which gives you 100% in each >> branch. Same thing. >> >> And because it’s the same thing you already know that you cannot derive this >> detector definition from the Schrödinger equation. > > ?? You can't derive the definition of any physical object from the > Schroedinger equation. You put in the Hamiltonian of the object and whatever > it interacts with and the initial ray in Hilbert space and the Schroedinger > equation tells you how it evolves > >> It’s not possible. What the many worlds people are now trying instead is to >> derive this postulate from rational choice theory. But of course that brings >> back in macroscopic terms, like actors who make decisions and so on. In >> other words, this reference to knowledge is equally in conflict with >> reductionism as is the Copenhagen interpretation. > > I agree with that point. But once you suppose a probabilistic interpretation > of the Hilbert space, then Gleason's theorem implies the Born rule. That > still leaves a small gap in saying why it has probabilistic interpretation at > all. Whether "self-locating uncertainty" is an adequate answer seems to me > to require more analysis of human thought; although showing the brain is a > quasi-classical information processor goes a long way. > > Brent > >> >> And that’s why the many worlds interpretation does not solve the measurement >> problem and therefore it is equally troubled as all other interpretations of >> quantum mechanics. What’s the trouble with the other interpretations? We >> will talk about this some other time. So stay tuned. >> >> @philipthrift >> >> > > > Sabine later goes on in a comment to say that > > "to correctly sum up the total energy, you have to weigh the energy in > each branch > with the probability of that branch" > > > In the end, I think Sabine's application of probability is a mess. > > And to put "self-locating uncertainty" into the mix (now QM is human-brain > dependent) makes things worse. > > I posted a course notes of a pedagogical approach of applying probability > theory to the conventional Hilbert space QM here: > > Quantum Probability Theory (by Jan Swart) > > https://groups.google.com/d/msg/everything-list/8_RCIBNbOis/0Qnlt_GyBQAJ > > So QPT and QMT (Quantum Measure Theory, by Rafael Sorkin) both take > probability seriously in a mathematically pedagogical way, but in Many Worlds > (Interpretation) it just looks like a Mega Waste.
It is an economy of principles, especially with Mechanism, where there is no world at all, as there is only histories corresponding to the computations, which exists in all theories capable of explaining the existence of computer. Bruno > > > @philipthrift > > -- > 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 view this discussion on the web visit > https://groups.google.com/d/msgid/everything-list/3ac9a8af-94a0-40aa-908d-c27cfa3cc4bb%40googlegroups.com > > <https://groups.google.com/d/msgid/everything-list/3ac9a8af-94a0-40aa-908d-c27cfa3cc4bb%40googlegroups.com?utm_medium=email&utm_source=footer>. -- 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 view this discussion on the web visit https://groups.google.com/d/msgid/everything-list/EECE14AC-CEC7-4A69-853A-91411BD2C89B%40ulb.ac.be.
