> On 12 Aug 2019, at 04:06, Bruce Kellett <[email protected]> wrote: > > On Mon, Aug 12, 2019 at 3:48 AM Bruno Marchal <[email protected] > <mailto:[email protected]>> wrote: > On 9 Aug 2019, at 13:15, Bruce Kellett <[email protected] > <mailto:[email protected]>> wrote: >> On Fri, Aug 9, 2019 at 7:49 PM Bruno Marchal <[email protected] >> <mailto:[email protected]>> wrote: >> On 9 Aug 2019, at 04:07, Bruce Kellett <[email protected] >> <mailto:[email protected]>> wrote: >>> From: Bruno Marchal <[email protected] <mailto:[email protected]>> >>>>> On 8 Aug 2019, at 13:59, Bruce Kellett <[email protected] >>>>> <mailto:[email protected]>> wrote: >>>>> >>>>> On Thu, Aug 8, 2019 at 8:51 PM Bruno Marchal <[email protected] >>>>> <mailto:[email protected]>> wrote: >>>>> If the superposition are not relevant, then I don’t have any minimal >>>>> physical realist account of the two slit experience, or even the >>>>> stability of the atoms. >>>>> Don't be obtuse, Bruno. Of course there is a superposition of the paths >>>>> in the two slit experiment. But these are not orthogonal basis vectors. >>>>> That is why there is interference. >>>> >>>> But each path are orthogonal. See the video of Susskind, where he use 1 >>>> and 0 to describe the boxes where we can find by which hole the particles >>>> has gone through. Then, without looking at which hole the particle has >>>> gone through, we can get the interference of the wave which is obliged to >>>> be taken as spread on both holes, and that represent the superposition of >>>> the two orthogonal state described here as 0 and 1. >>> I seldom watch long videos of lectures. But if Susskind is saying that the >>> paths taken by the particle through the two slits are orthogonal then he is >>> flatly wrong. Writing the paths as 1 and 0 does not make them orthogonal. >>> And if they were orthogonal they could not interact, and you would not get >>> interference. Two states |0> and |1> are orthogonal if their overlap >>> vanishes: <0|1> = 0. Interference comes from the overlap, so if this >>> vanishes, there is no interference. >>> Either Susskind is terminally confused, or you have misrepresented him. >>> >>> >> Or maybe you are wrong. Slit one is orthogonal to slit two, as much as spin >> in different direction. >> >> When you observe which slit the particle went through, then yes -- the slits >> are then orthogonal eigenstates of the position operator. > > OK. But without collapse, the observation of which slit the particle was > taking is only self-entanglement, and it makes the whole history “the > particle went through slit A + me seeing the particles going through slit A” > orthogonal to the whole history “the particle went through slit B + me seeing > the particles going through slit B”. > > So, like I said, the slits are orthogonal if measured. This is irrelevant to > the interference at the screen, because it is the photon waves at the screen > that interfere, not the slits. Orthogonal states do not interfere. > > Decoherence is only self-entanglement. It spread at the speed of light, or a > bit below, in the environment, making hard to fuse the histories again, > through “amnesia”, but that explains why the superposition states are are > hard to maintain accessible. FAPP, we can forget the parallel histories, but, > only FAPP! > > FAPP is the way we do physics. Metaphysics is for the birds that can't fly! > >> The interference comes from the fact that we get a superposition of going >> through slit one + going through slit two when we send a planar >> monochromatic wave on the wall with the two slits, and don’t measure which >> slit the particle go through. >> >> Yes, then the states that we are measuring are not orthogonal. You do not >> get interference between orthogonal states. >> >> That is how Susskind explains the two slit experiment in term of >> entanglement. You don’t need to look at the whole video, I gave the position >> of this sub-talk in the video. >> >> Any crisp measurement, like “which slit” gives rise to orthogonal state, >> which can interfere when superposed. >> >> Which is essentially what I said -- orthogonal states do not interfere. > > In the sense you mention I am OK, but we have a slight vocabulary problem. > Not important, if you agree that measurement are self-entanglement, so that > the superposition of the orthogonal state SlitA and SlitB, say some oblique > (with sqrt(2) = 1) SlitA + SlitB is inherited by the observer “looking” which > is which. > > If you do not measure which slit the photon went through, then the > superposition of slits is not broken by decoherence.
Decoherence break things only if there is a collapse. Without collapse, even if I measure which slit the photon went through, the two terms of the superposition continue to exist, describing me seeing both outcomes, and both me feel like if there has been a collapse, and that decoherence is physical real, but that illusion is explained by the formalism, in a manner similar to the WM duplication: it is just first person indeterminacy, not in a self-duplication, but in a self entanglement. Bruno > But the interference at the screen depends only on things like the wavelength > of the light, the separation of the slits, and the distance between the slits > and the screen. If you refine this calculation by taking the finite width of > the slits into account, you convolute the interference pattern with the > diffraction pattern due to finite slit width. This is an elementary > calculation in physical optics, not even requiring quantum mechanics. But the > waves at the screen cannot be orthogonal, or else they would not interfere. > > 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] > <mailto:[email protected]>. > To view this discussion on the web visit > https://groups.google.com/d/msgid/everything-list/CAFxXSLRmoV5fKbbyLUfhbrZtzGUF23d%3Dq_RHyuyzDfq%3DPP2arA%40mail.gmail.com > > <https://groups.google.com/d/msgid/everything-list/CAFxXSLRmoV5fKbbyLUfhbrZtzGUF23d%3Dq_RHyuyzDfq%3DPP2arA%40mail.gmail.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 [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/everything-list/C30C1EF1-B7A5-4ECA-B5FD-B026BDF89E0F%40ulb.ac.be.
