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Good evening citizens and non-citizens, On Thu, Oct 14, 2010 at 08:21:19AM -0700, William G. Scott wrote: > On Oct 14, 2010, at 7:40 AM, Ed Pozharski wrote: > > > On Thu, 2010-10-14 at 08:41 +0200, Tim Gruene wrote: > >> This sounds as though you are saying that a single photon interacts > >> with several > >> electrons to give rise to a reflection. > > > > Not only with several - it shouldn't be much of an exaggeration to say > > that the photon senses all the electrons in the Universe as it travels > > between the source and detector. Once it hits detector, it's trajectory > > magically collapses into a specific one. Quantum physics is undeniably > > crazy stuff :) > > > > Cheers, > > > > Ed. > > Less ephemerally, the photon scatters from every scattering center in the > crystal lattice. Under these (incoherent scattering) experimental conditions, > it is my understanding that the individual photon only interferes with itself. I would like to understand how the notion of a photon being scattered from all electrons in the crystal lattice explains the observation that radiation damage is localised to the size of the beam so that we can move the crystal along and shoot a different location. > > The "quantum weirdness" creeps in from the fact that the wave describing the > scattering is spherically symmetric, sampled by the reciprocal lattice. But if a > photon is a particle, and you were to do a single photon experiment, the particle > of light can only wind up in one of the diffraction spot locations, but the diffracted > wave determines the propensity of the photon to wind up in that location. It is > basically the generalization of the single photon double-split "paradox." The double slit paradox is actually not a paradox, and a single photon is not scattered by both slits: if you reduce the light intensity so that you really detect single photons, you observe that each photon decides on exactly one slit that it goes through. It is only the sum of many photons that create the typical pattering of the double slit experiment. The photon knows it is both wave and particle, but depending on the experiment we carry out we observe only one of the two phenomena, but never both. That's also the idea behing Schroedinger's cat. Cheers, Tim > > I've found the headaches start to go away if you don't take the "duality" part of > wave-particle duality too seriously. > > -- Bill -- -- Tim Gruene Institut fuer anorganische Chemie Tammannstr. 4 D-37077 Goettingen phone: +49 (0)551 39 22149 GPG Key ID = A46BEE1A