![]() An individual particle cannot interfere with itself. 12 – 16įor clarity, it is important to emphasize here the distinction between diffraction, which relates to the scattering and probability distribution for individual photons, and interference, which is a cooperative phenomenon that relates to the probabilities of detection (absorption?) when there is a multiplicity of photons (e.g., two electromagnetic beams) that can influence each other at the point of detection. This picture is important as it illuminates our debates over the wave-particle nature of light and quantum uncertainty, framing the contrasts between the standard (Copenhagen) interpretation and several alternative interpretations. The current paper compares and contrasts MET with optical wave theories to elucidate these underlying momentum exchange selection rules. 2, 5 This picture is conceptually flawed as the probability must be determined at the location of scattering to conform to conservation of momentum. Classical optical wave (COW) theory leaves us with an erroneous understanding of diffraction in suggesting that the probability for detecting a diffracted photon is determined on observation at the point of detection. The distinct feature of MET is this dependence on the specific path of the scattered particle and location of momentum transfer. 8 – 11 MET starts from a momentum representation for scattered particles and postulates the probability distribution for diffraction scattering is determined by at least two important factors: (1) the momentum transfer states of the scattering lattice and (2) the distance over which momentum is transferred between the lattice and scattered particle. 2 – 6 MET draws from the early ideas of Duane 7 and later formalized by Landé. ![]() ![]() Momentum exchange theory (MET) is presented as an alternative picture for photon diffraction based upon quantized momentum transfer with the scattering lattice or aperture. Early days of X-ray Crystallography (International Union of Crystallography/Oxford Univ.“It seems to be a characteristic of the human mind that familiar concepts are abandoned only with the greatest reluctance, especially when a concrete picture of phenomena has to be sacrificed.” ![]() The crystal space-lattice revealed by Röntgen rays. Eine quantitative prüfung der theorie für die interferenz-erscheinungen bei Röntgenstrahlen. Interferenz-Erscheinungen bei Röntgenstrahlen. Über eine berechnung der wellenlänge der Röntgenstrahlen aus dem Planckschen energie element. When they added a photographic plate behind the crystal, Friedrich and Knipping finally recorded traces of the diffracted beam, proving that the intuition of von Laue was true, though only in part ( Milestone 3). Looking for interference from an isotropic radiation, they first positioned a collecting photographic plate parallel to the primary X-ray beam, but detected no signal. The two physicists used a powerful X-ray bulb and collimated a narrow primary beam on several crystals (copper sulphate pentahydrate and zinc sulphide, in particular) that, according to previous studies, contained metallic species showing strong X-ray fluorescence. Nevertheless, in April 1912 von Laue was able to secure the help of two brilliant experimentalists, Walter Friedrich and Paul Knipping, to test his hypothesis. ![]() At the beginning, this idea received some opposition indeed, both Sommerfeld and Wilhelm Wien doubted that the emission coming from these atoms would be coherent and thought that the interference would be destroyed by thermal motion of the crystal. ![]()
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