On Mon, Jul 5, 2021 at 7:39 PM smitra <[email protected]> wrote: > On 05-07-2021 09:00, Bruce Kellett wrote: > > On Mon, Jul 5, 2021 at 2:23 PM smitra <[email protected]> wrote: > > > > I don't think this is actually done in the experiment. What is > > observed is the presence or absence of the interference pattern on the > > screen where the balls hit. The photons are not detected. But if, in > > principle, they are of suitable wavelength to resolve the slit > > difference, then the interference pattern vanishes. The experiment is > > convincing in that they start wil cold buckyballs which show a clear > > interference pattern. They then gradually heat the balls so that the > > typical wavelength of the photons decreases. This gradually washes out > > the interference pattern. (Because at lower temperatures, the > > wavelength distribution of the IR photons is such that a few of them > > have shorter wavelengths.) As the temperature is increased so that > > most IR photons have short enough wavelengths, the interference > > pattern disappears completely. The paper by Hornberger et al. is at > > arXiv:quant-ph/0412003v2 > > This is then what I said previously, what you denied, i.e. that you are > only considering part of the system which is defined by the reduced > density matrix. The complete system of buckyball plus photons will show > interference, even if the wavelength is small enough to resolve the > slits provided you perform the right sort of measurement on the balls > and photons. >
That is false. > > > > This is not what happens. Read the paper referenced above. > > It's not what happens in that experiment, but you can in principle > demostrate an interference pattern also when photons are emitted by the > balls. > Provided the wavelength of the IR photons is too large to resolve the inter-slit distance. When you heat the balls further, the interference disappears. > > > This is all totally irrelevant to the actual experiment in question. > > > > And that experiment is in turn irrelevant to the question of whether or > not a real superposition actually exist. You can always perform a > measurement involving more particles where an interference has vanished, > that only demonstrates that the reduced density matrix described a mixed > state, the entire system is still in a pure state. > Of course real superpositions exist. The experiment shows that decoherence need not involve large numbers of degrees of freedom. > > > These considerations do apply to each and every case. I mentioned the > > buckyball experiment because it makes things obvious. But the general > > principle is always true. Experiments that produced recorded results > > are not reversible. Because, for example, they are not thermally > > isolated, and IR photons can always escape to infinity and be > > irretrievable. > > Even if IR photons always escape to infinity, the complete quantum state > of the entire system is still a pure state. There is still a > superposition between the balls going through one and the other slit. > Maybe that is not what is observed. That superpostion has decohered. > > >> For example, one may object by invoking that the universe is > >> filled with a plasma and that the IR photons travel at a speed > >> slightly below the true vacuum speed of light. > > > > What difference would that make. The IR photons are still faster than > > any material object sent after them to capture them. They will always > > escape. And because the universe is expanding, they will eventually > > pass over the Hubble horizon and be forever lost from sight! > > > > But the observations on the balls will be completed long before that, so > how is this relevant for the existence of parallel worlds? > I think it is relevant to the question of reversibility. > > > Whether this means that the off-diagonal terms of the density matrix > > (in the appropriate basis) do actually vanish, or if this is achieved > > by some other means, your theory has to adapt to the reality of > > irreversibility or your theory does not describe the real world. It is > > clear that for many reasons, pure Everettian QM, based solely on the > > Schrodinger equation, fails to explain many important features of the > > world we observe. > > > Which would mean that QM cannot be correct as a fundamental theory. > It is very probable the QM, in its current form, is not the correct fundamental theory. In the history of science it is never the case that the dominant theory at one time survives unaltered into the future. The negative induction against scientific realism is that all scientific theories are ultimately shown to be false. Bruce -- 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 view this discussion on the web visit https://groups.google.com/d/msgid/everything-list/CAFxXSLR%3De%2BDdQHS_QCECFsf-Yt2NbFQw7gUPf7tpVpLjTB%2B_QQ%40mail.gmail.com.
