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|2-1: Young's Experiment, the Wave Nature of Electrons|
[The Double-Nature of Light]
First, let us review on the duality briefly.
As explained on the pages, 3-8: Summary of Part 3 and Epilogue : Opening to Quantum Mechanics, in the previous Seminar, the wave nature of light was confirmed by Young's double-slit experiment. The photograph of the interference fringes in Young's experiment shown below is, so to speak, the result of a cooperative work of the particle nature and the wave nature of light. You should keep this in mind.
On the other hand, the particle nature of light was established by Einstein's hypothesis of photon based on Planck's energy quantum and its experimental confirmation.
A monochromatic light from a point source passes through the two thin slits, S1 and S2, and makes an interference fringes on the screen.
An example of
the interference fringes
in Young's experiment
is shown in the following
represents the picture
of the pattern on the screen
when only one of the slits is open,
shows the picture
of the striped pattern
on the screen
when both the slits are open.
[The Wave Nature of Electrons]
Since the discovery of electron by J. J. Thomson, nobody had doubted that an electron is a very small and very light particle seemed as almost one point, whereas it has been clarified after the proposal of matter wave by de Broglie that electrons possess not only particle nature but also wave nature. It has been confirmed that other substance particles as well as electrons have the duality of particle nature and wave nature.
[Abandon the Idea of Choice
between Two Alternatives]
At the beginning of the 20th century, physicists in the world came up against the serious contradiction between the particle nature and the wave nature.
Is this a true contradiction? We think that light or an electron must be a particle or a wave, exclusively. Is this the reason why we feel the particle-wave duality as a contradiction? The idea that we have to choose between two alternatives, "particle" or "wave" might be a classical thinking way. Isn't it possible to consider that the duality might be an essential quality of matter? It was discussed that the photograph of the interference fringes in Young's experiment shown above is a cooperative work of the particle-wave double natures of light. The photograph cannot exist without any of the two natures. This thoroughly deny the above-mentioned idea of choice between two alternatives.
As learned on the page, 1-5: The Meaning of the Wave Function, we know that the wave function represents the probability that the particle will be found; precisely speaking, the square of the absolute value of the wave function represents the probability. You may be enough wise to notice that we can unify the particle nature and the wave nature within quantum mechanics by introducing the concept of probability without adopting the idea to choose between the two alternatives. Let us discuss this in further detail on the following pages.
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