On 10/15/10 12:38, Bart Hazes wrote: > The photon moves through the crystal in finite time and most of the time > it keeps going without interacting with the crystal, i.e. no > diffraction. However, if diffraction occurs it is instantaneous, or at > least so fast as to consider it instantaneous. In some cases a > diffracted photon diffracts another time while passing through the > remainder of the crystal. Or in Ruppian terms, a poof-pop-poof-pop > event. If you listen carefully you may be able to hear it. >
The photon both diffracts and doesn't diffract as it passes through the crystal and it diffracts into all the directions that match the Bragg condition. The wave function doesn't collapse to a single outcome until the detector measures something - which in the scheme of things occurs long after the photon left the crystal. The photon also interacts with the electrons for as long as the wave functions overlap. You have to solve the time-dependent Schrodinger equation to get the details. In all the the QM classes I've had they start by writing the time-dependent equation and then immediately erasing it - never to be mentioned again. All the rest of the term was spent with the time-independent equation and the approximation of the "instantaneous quantum jump." If you assume that nothing changes with time the only way to model changes is with discontinuities. Dale > Bart > > On 10-10-15 12:43 PM, Jacob Keller wrote: >>> >but yes, each "photon" really does interact with >>> EVERY ELECTRON IN THE CRYSTAL at once. >> >> A minor point: the interaction is not really "at once," is it? The >> photon does have to move through the crystal over a finite time. >> >> JPK >
