On Thu, Oct 17, 2019 at 8:51 AM John Clark <[email protected]> wrote:
> On Wed, Oct 16, 2019 at 4:49 PM 'Brent Meeker' < > [email protected]> wrote: > >> * > I thought you read Carroll's book. His example shows in what sense >> you can erase the information after the photon has hit the screen.* >> > > If you wait to erase the which way information until after the photon has > hit the screen then the experiment would be much easier to perform, but the > results of it are obvious and rather dull, you would see interference bands > because there would be ambiguity over which slit the photon went through. > The more interesting thing to do is to make the decision on whether to > erase the which way information or not to erase it until after the photon > passes the slits but before it hits the screen; it turns out that if you > decide to not erase the information then you don't get a interference > pattern, but if you decide to erase it then you do get a interference > pattern. And that exparament has already been performed and yes the results > are weird because the decision to erase or not to erase the information was > made long after, even billions of years after, the photon passed the slits > so you might think it would make no difference as far as the picture on the > screen is concerned, but it does. > > And I think all of this is super interesting, *but* it is *not* the > experiment Deutsch proposed. And you still haven't told me what your best > guess is that Deutsch will find when he develops that all important > photographic plate; will he see interference bands or no interference > bands? I've already told you how I'd place my money. > The quantum erasure-delayed choice experiments that have been done, and discussed by Carroll (in his book and on his blog) are entirely equivalent to Deutsch's thought experiment. The decision to erase or not erase the welcher weg information until after the photons have hit the screen was a central feature of these experiments -- making the results more significant than if the information was erased *before* the photons hit the screen. Exercise: Explain why the experimenters took trouble to do it *after* the photons hit the screen! I think the interesting fact is that in the experiments (see Wikipedia), and in Carroll's account and explanation, the assumption of many worlds plays an entirely insignificant role -- the explanation of delayed choice and quantum erasure goes through just as well in a single world as in many worlds. Deutsch was simply wrong when he thought that his experiment would "prove" the existence of many worlds. The existing experiments show this conclusively. The effect is real, but do not require many worlds. 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/CAFxXSLSQpX%3D2j3GmHfoMkuHoYDKCwpdeOKDxHuMdsqv18T3MwQ%40mail.gmail.com.
