On Sat, Oct 19, 2019 at 1:39 AM John Clark <[email protected]> wrote:
> On Thu, Oct 17, 2019 at 5:35 PM Bruce Kellett <[email protected]> > wrote: > > *> I see, Deutsch was testing the idea that it was consciousness that >> collapsed the wave function. But, apart from a few flirtations with the >> idea, none has ever taken that seriously. It is certainly not part of the >> Copenhagen Interpretation.* [...] *given SR, there can be no signal >> informing one observer of the other's results.* >> > > I see.... no I take that back I don't see. You used a very odd word in > the above that I don't understand at all, the word is "observer". > And you dishonestly deleted all the intervening explanatory text. > *> if you erase or not the welcher weg information 'before' the signal >> photon hits the screen, then presumably some, presently unknown physics, >> could send this information to the screen and influence the result there.* >> > > So you admit it. If you continue to insist Many Worlds do not exist then > to explain an experiment that has been performed many times you must > postulate new physics and mess with Schrodinger's Equation. > Not at all. The results of the experiment are easily explained within the structures of conventional quantum mechanics, whatever interpretation one wishes to adopt. There is nothing mysterious here. > *> The reason for erasing or not *after* the signal photons hit the screen >> is to eliminate this possibility -- any signal to the screen would have to >> be backwards in time.* >> > > If you decide to erase or not to erase after the photon passes the slits > but before it hits the photographic plate then to explain the results > you've either got to embrace Superdeterminism, backward causality or Many > Worlds. > No, you have got it wrong here. No need for any of this. If you erase the information after the photon hits the photographic plate > then you don't have to embrace anything because the experiment would tell > you nothing. It's called The Wheeler Delayed Choice Experiment but it was > actually first proposed in 1926 by Gilbert Lewis (he also coined the word > "photon"), but it remained just a thought exparament for 81 years and was > not actually performed until 2007. > > Experimental realization of Wheeler’s delayed-choice GedankenExperiment > <https://arxiv.org/pdf/quant-ph/0610241v1.pdf> > > Why do you suppose that is, why the big delay between thought experiment > and real experiment? Because although it's simple in concept it's very > difficult to actually perform, you need super fast electronics and a very > good random number generator to make the split second decision to erase or > not to erase in the ultra short amount time between the photon passing the > slit and it hitting the photographic plate. If you could take your time and > wait until after it hit the plate Lewis could have not just talked about it > but actually done the exparament in 1926 and he wouldn't have needed > advanced electronics; steam powered, or even horse powered, machinery > would have been good enough. > The decision to erase or not to erase is made at a space-like separation from the screen in the experiment you cite. This was done, presumably, to eliminate the possibility of unknown physics informing the photons in-flight, or at the screen, about what choice was made. Delaying the choice until after the photons hit the screen achieves the same end. Why do you think it is called "delayed choice" after all? >> After? Took the trouble? After would be easy, and pointless. It is much >>> more difficult to erase the which way information *after* the photons >>> hit the slits but *before* they hit the screen, it would also be far >>> more informative. >>> >> >> The interference pattern is present if the welcher weg information is > erased, > > Yes, > > >> *> whether the erasure takes place before or after the photons hit the >> screen.* >> > > Yes but you can't expect to learn anything if you look at the developed > photograph and then decide whether to erase the which way information or > not. If you decide to erase the information do you imagine you will see the > photograph change before your eyes?? > Yes, of course you do: you just select the subsets of photons that were quantum-erased by passing the left polarizer (respectively, the right polarizer) to see the interference patterns emerge from the apparent no-interference blob. I think you should go back and read Sean Carroll's account of this (on his blog, or in his book) a bit more carefully. You could even go the the Wikipedia page on this: https://en.wikipedia.org/wiki/Delayed-choice_quantum_eraser to see how it works. > *If the welcher weg information is quantum erased, then there will be an >> interference pattern, whether or not it is a conscious observer who is >> erased.* >> > > If that's the way the exparament turns out and a interference pattern > exists but Many Worlds does not exist then how do you explain the existence > of a signed document testifying that somebody observed the photon going > through one and only one slit and the he knew which one? Inquiring minds > want to know. > The signed document is irrelevant because it does not contain the welcher weg information. Many worlds has nothing to do with it. I am assuming that when you say the information was erased from the QC memory, then you mean completely erased, no traces left anywhere. Failure to completely erase the information, even if it is not easily accessible, will result in loss of the interference patterns. I really do think that you have to do a bit more work in order to understand what is going on here. 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/CAFxXSLQ%3DfP%3DvbqcFTiye9cK_67gFVyjTL_A35Q6YNNaVVB3Bww%40mail.gmail.com.
