On Wed, Aug 7, 2019 at 7:31 PM Bruno Marchal <[email protected]> wrote:
> On 7 Aug 2019, at 00:37, Bruce Kellett <[email protected]> wrote: > > On Wed, Aug 7, 2019 at 4:00 AM 'Brent Meeker' via Everything List < > [email protected]> wrote: > >> >> In something like Shor's algorithm there is only one final state with >> non-vanishing probability. >> > > Exactly. So there are no other components in superposition. Bruno wants to > characterize this as a collapse. But without this happening, the QC would > be unreliable -- there would be some finite probability that you would get > the wrong result. As I understand it, there are some QC algorithms that do > not lead to definite results, so you have to run them several times to > reduce the probability of a wrong answer to some acceptable level. > > As usual, Bruno is introducing irrelevancies in order to distract > attention from the fact that he cannot answer the central contention of my > argument -- which is that quantum computer do not provide any evidence for > the existence of parallel worlds. They can work perfectly well in just one > world -- without any collapse whatsoever. > > > I can’t explain even just the two slits without superposition. > Superpositions are fine. It is just that they do not consist of "parallel worlds". > “Parallel worlds/histories” are just a popular name to describe a > superposition. > In your dreams, maybe. There is a clear and precise definition of separate worlds: they are orthogonal states that do not interact. The absence of possible interaction means that they are not superpositions. Then nothing in the QM linear evolution can explain how the superposition > disappear, > Yes there is. If the dynamical evolution leads to zero coefficient for some branch, then that branch drops out of the superposition. If all branches but one go to zero in this way, then the superposition disappears. > although the decoherence theory explain why it is hard to see a > macro-superposition. > Shor algorithm does not make them disappear, even if it manages to get the > result with high probability in the branch we are situated in. > If the coefficient of a branch in the wave function vanishes exactly, then the probability of obtaining that result is zero. The branch with zero coefficient is no longer present in the superposition -- exactly, and not merely FAPP. The effective quantum computer sets all branches to zero except the branch corresponding to the required result. There is no residual superposition. 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/CAFxXSLSJgEiNLM6kAhfh3LxYZQOYfUp00Ftp2%3DN%2BO4JOmcoGrA%40mail.gmail.com.
