On Friday, December 8, 2017 at 6:19:20 PM UTC, Brent wrote: > > > > On 12/8/2017 12:01 AM, [email protected] <javascript:> wrote: > > > > On Thursday, December 7, 2017 at 11:54:39 PM UTC, Bruce wrote: >> >> On 8/12/2017 10:40 am, [email protected] wrote: >> >> On Thursday, December 7, 2017 at 4:44:01 PM UTC, Bruno Marchal wrote: >>> >>> >>> >>> Yes, but only if the phase are indeed different at each slits, I would >>> say. The interference pattern would shift. >>> >> >> >> >> >> >> >> >> *I had a confusing and testy response from Bruce on this issue. To >> recapitulate: AG> Are the phase angles of components of a superposition >> identical? If so, is this the definition of coherence? TIA, AG BK> No, why >> should they be equal. You really do have to learn some basic quantum >> mechanics, Alan, and stop bothering the list with such questions. I might >> be mistaken, but In the double slit I think the phase angles must be equal >> to get the interference pattern observed, and if they're different at each >> slit, we won't get what's observed. And if each component of a >> superposition with many components has an arbitrary phase angle, I don't >> see how we get coherent waves. I know this is not an interesting issue for >> Bruce, but maybe he will clarify the situation. IIRC, on another message >> list, Roahn, a Ph'D physicist known to Bruce, claimed the phase angles of >> components of a superposition are equal. It would seem so, for if one has a >> solution of the SWE and assigns a phase angle arbitrarily, and then expands >> the solution in some basis, I think the basis vectors would inherit the >> same phase angles. Still studying Bruce's link! * >> >> >> Bruno is right on this -- the only effect of changing the phase in one >> arm of the superposition would be to shift the interference pattern to the >> side, it would still be the same pattern. >> > > *That's what I was trying to say above; shifting the pattern would be a > new result IMO, same form but shifted in one direction. What I was puzzled > about was the relation of the phase factors to coherence. If the > superposition consists of three components with each pair of phases being > multiples of each other, but not all three. Would the resultant > superposition still be considered to be coherent? (not discussed in any > links I can find). AG* > > > The superposition is considered to be not coherent in the FAPP limit where > there are many components with different varying phases (different > frequencies) so the cross-terms of the density matrix tend to average to > zero. This is the situation when the system includes the instrument and > the environment. In theory the system+instrument+environment is in a > superposition but almost all of its components are unobservable so we > regard it as decohered. > > Brent > > >> This is explained in the Wikipedia page I referenced. Linearity of the >> SWE means that the sum of any two solutions is also a solution, but the >> individual solutions can be added with arbitrary complex weights (phases). >> The overall phase has no physical consequences, but the relative phase is >> all-important. There is no reason for the relative phases to be equal, they >> can be anything at all. >> > *Bruce; bear with me on this one. IIRC, Roahn claimed the phases are equal. I think he was referring to the case of a solution of the SWE which has an arbitrary phase assigned, and is then expanded into a superposition in some basis. In this *particular* case, I believe the components would inherit the phase of the original wf. If the phases of the components are different from the original assigned phase of the original wf, I don't think the sum would represent the original wf. Is this correct? AG *
> So in the two-slit experiment, putting a phase changer in one arm simply >> shifts the pattern to the left or the right. This experiment has been done. >> >> This is elementary quantum mechanics, and the details are readily >> available on-line or in text books. >> >> 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 post to this group, send email to [email protected]. Visit this group at https://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
