The Electron Double-Slit Experiment
The electron double-slit experiment was eventually performed in 1961, by Claus Jönsson of Tübingen; during a fellowship at the University of Tübingen in 1973 and 1974, Tonomura worked with Gottfried Möllenstedt, who was the first researcher to observe electron interference patterns (electron diffraction patterns) by developing electron biprism interferometers; the single electron double slit experiment was performed by Pier Giorgio Merli, Gian Franco Missiroli and Giulio Pozzi in Bologna in 1974, and repeated by Akira Tonomura and co-workers at Hitachi in 1989. The effort of these researchers is in fact an important step toward rejecting the existing unrealistic concept in quantum mechanics, namely “wave-particle duality” which is known as complementarity principle in Copenhagen Interpretation.
Let us concentrate our attention on the final words of Akira Tonomura about the outcomes of experiment that was carried out at Hitachi:
“ We have reached a mysterious conclusion. Although electrons were sent one by one, interference fringes could be observed. These interference fringes are formed only when electron waves pass through on both sides of the electron biprism at the same time but nothing other than this. Whenever electrons are observed, they are always detected as individual particles. When accumulated, however, interference fringes are formed. Please recall that at any one instant there was at most one electron in the microscope. We have reached a conclusion which is far from what our common sense tells us.”
According to a principle in physics, interference is the addition (superposition) of two or more waves resulting in a new wave pattern. Consequently, it is believed that in double-slit experiment the fringes are formed due to interference of two combining waves, such as: light waves, photon waves, matter waves or even electron waves! But, is it really possible to have an interference pattern when electrons were sent one by one in the electron double-slit experiment? No, it isn’t. On the other hand, how can an electron interfere with itself?It must be more questionable for those who think, without any scientific basis, particles such as photons or electrons have wave-like behaviour as well. Anyhow, the fringes are formed and even observable. We need therefore to find the cause of formation of fringes in double-slit experiment.
Before investigation into the reason of formation of double-slit pattern, it would be helpful to have a relatively clear picture about the emitter of electrons in this experiment. Usually electron microscopes utilize an electron source with a Thermionic Gun in which electrons are released from a resistively-heated tungsten filament (cathode). In other words, by heating the filament the most energetic electrons of tungsten atom, which gather in outermost orbital, gain sufficient energy to overcome the work function barrier and move toward the anode. These electrons later used for imaging are emitted from a nearly perfect point source (the space charge). Therefore, it is reasonable to conclude that the bright spots on the monitor represent at random positions the outer orbital electrons of a huge number of tungsten atoms. It should be reminded that generally it is told the atom of tungsten has only two electrons in its outermost orbital.


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