On 8/12/2017 10:40 am, agrayson2...@gmail.com 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.
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. 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
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