On Mon, Aug 12, 2019 at 4:09 PM Bruce Kellett <[email protected]> wrote:
> On Mon, Aug 12, 2019 at 3:56 PM smitra <[email protected]> wrote: > >> On 12-08-2019 04:06, Bruce Kellett wrote: >> > On Mon, Aug 12, 2019 at 3:48 AM Bruno Marchal <[email protected]> >> > wrote: >> > >> > 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. 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. >> >> The states at the screen are orthogonal because they were at the start >> and inner product is conserved under the unitary time evolution. >> > > The sits are orthogonal if you measure which slit the photon went through, > in which case the interference pattern disappears, as required by > orthogonality. But they are not orthogonal if they are not measured, else > there would be no interference. Orthogonal states cannot interfere. > Look at this another way. It is just an illustration of complementarity. Measuring which slit the photon went through is a position measurement at the slits. Measuring the interference pattern at the screen is equivalent to a momentum measurement at the slits. Such measurement operators do not commute -- the measurements are complementary and cannot be performed simultaneously. 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/CAFxXSLQw5piLk6TAsAeExB0%2BG1dqEMNts0d-gNz%3DzgN0%3D-ZGAg%40mail.gmail.com.
