Single electron double slit experiment is the most basic and important experiment in quantum mechanics. In 2002, Physical World magazine in the United States rated it as the first of the top ten most outstanding experiments in physics [1], which can also be said to be the most magical physical experiment in human history. This little experiment showed the duality of wave and particle and the singularity of quantum mystery to the fullest, which greatly impacted our world view and puzzled many physicists including Einstein for a long time. The explanation of this experimental phenomenon is still controversial. Richard feynman, a physicist, said: "The single electron double-slit experiment contains the core of quantum mechanics. In fact, it contains a unique mystery. We can't solve the mystery by explaining how it works. We just tell you how it works. While telling you how it works, we will also tell you all the basic characteristics of quantum mechanics. " [2]
Single electron double slit experiment is the most rigorous and reliable empirical phenomenon, and it is also the most profound and difficult empirical phenomenon. This is also the only physical experiment that must consider the observer's consciousness. It is the most reliable logical starting point of philosophical thinking, which contains almost all major problems and fundamental mysteries of philosophy. Almost all major philosophical issues are involved, such as reality and anti-reality (ontology), apriori and experience (epistemology), causality (Schrodinger's theory of evolution and Dirac's choice), free will (Heisenberg's choice), logic theory (formal logic, dialectical logic and quantum logic), the essence of time and space (binary time and space) and the interaction between mind and matter (coherent superposition), and even the soul is implied. It can even be said that taking the single electron double slit experiment as the basic point of Archimedes' philosophical thinking can shake the whole universe.
For this experiment, you can look at the following animation demonstration in detail, which vividly demonstrates the magical phenomenon of electronic double-seam experiment.
In the electronic double-slit experiment, when we hit a beam of electrons on the final display screen through the middle double-slit, according to experience and common sense, the electron is just a single tiny granular object like a football. In the daily world, if we play a lot of football in a row and go through a wall with two slits in the middle, then only two stripes will be formed on the net, and it is impossible to form multiple interference stripes. However, the results of electronic double-slit experiment seriously deviate from our common sense and experience, and finally form interference fringes on the screen that only waves can form.
So will a large number of electrons collide with each other? If they collide with each other, it is indeed possible to change the path of electron movement. Although interference fringes may not be formed, this possibility should be completely ruled out. So we can improve the experimental device, let the electron gun emit electrons one by one, and the interval can exceed one second, and then see what the experimental results are.
When an electron is hit, only a bright spot appears on the screen. The more electrons pass through, the more bright spots appear. These dots are chaotic at first glance, but as time goes on, when more and more electrons are knocked out, a large number of dots formed by a large number of electrons gradually form interference fringes that only waves can form!
Since electrons are emitted one after another for a long time, it can be logically inferred that a single electron must be a ductile wave, and at the same time, it can interfere with itself through double slits, thus forming interference fringes that only waves can form, but how is this possible? An electron can't be a wave at all, because the waves we observe every day are multi-particle cluster fluctuations. How can a single local small particle be a broad group wave? How is it possible to pass through two slits at the same time like separation? This is one of the mysterious phenomena produced by the double-slit experiment.
In order to solve the above confusion, we need to observe how electrons pass through the double slit and whether there is really a magical "electron separation", so we installed a detector next to the double slit to see which slit the electrons pass through and how they pass. This experiment is called "which way to go" experiment, which was completed by Toure and Rempe of the University of Constance in Germany from 65438 to 0998. [3]
The experimental results once again exceeded people's imagination. When we went to observe how the electrons passed through the double slit at the same time through the detector, the electrons actually passed through a slit and the interference fringes disappeared! There are two classic bright stripes on the screen! In other words, a small observation actually changed the existence characteristics of electrons, making them change from fluctuations to particles. Why does observation have such a magical effect? Such experimental results are even more confusing to us. Why?
The single electron double-slit experiment was first proposed by physicist Feynman in 196 1 year. Because the gap size needed in this experiment is in the order of nanometers, the technical conditions at that time could not be realized. 1974, scientists Merli, Missiroli and Pozzi of the University of Bologna, Italy, conducted experiments on "single electron" [4]. They let a single electron pass through a biprism, which is an electro-optical device with similar function as a double slit. Let the electrons be emitted at intervals. Then the position of electrons is recorded on the screen, and finally the appearance of interference fringes is observed.
Feynman's single-electron double-slit experiment was really realized in 20 13 years, which was completed by American and Canadian scientists Roger Bach and Damian Pope [5]. They made a double seam with a width of 62 nm, a length of 4 microns and a seam spacing of 272 nm on the gold-plated silicon film. In order to cover one seam at a time, a tiny mask controlled by a piezoelectric actuator can slide back and forth between two seams. In the experiment, electrons are generated by tungsten wires, accelerated in an electric field of 600 volts, and then calibrated into electron beams. After the electrons pass through the double slit, they will be observed on the multi-channel photosensitive film. In this experiment, both slits can be opened and closed mechanically at will. The most important thing is that it has the function of detecting one electron at a time. In this experiment, the intensity of the electron source is very low, and only one electron can be observed per second, which ensures that only one electron will pass through the double slit at a time. After more than two hours of experiments, interference fringes still appear in the final experimental image.
From the earliest Young's double-slit experiment in 180 1 to the single-electron double-slit experiment in 20 13, the span reached 200 years, which witnessed the wave-particle duality and the magic of the quantum world.
The double-slit experiment strongly proves that matter particles are as volatile as electrons, but the understanding of the fluctuation of matter particles has experienced a long-term heated debate. Pioneers of quantum physics such as De Broglie and Schrodinger, including Einstein, have been influenced by classical physical concepts and made various mistakes. Even Einstein did not accept the understanding of wave-particle duality in quantum mechanics until his death.
The first explanation of the double-slit experiment is the pure particle view, which holds that electrons can only be particles, not waves. The formation of interference fringes is caused by the interaction between different particles. The so-called fluctuation is a density wave caused by the distribution of a large number of electrons in space, which is similar to the longitudinal wave of air vibration and also a wave distribution caused by the alternation of molecular density. But this view obviously contradicts the experimental phenomenon, because in the experiment, we let the electrons be emitted from the electron gun one by one. Although it is impossible to form interference fringes at first, as long as the time is long enough, light and dark interference fringes will still appear on the screen. This shows that when many electrons gather together in space, the fluctuation of electrons does not appear, and a single electron also fluctuates. Understanding electrons as pure particles exaggerates the particle surface and obliterates the fluctuation surface, which is a one-sided misunderstanding.
The second explanation of the double-slit experiment is the explanation of pure wave view, which holds that electrons are not discrete small particles, but three-dimensional continuous distribution of material wave packets, the size of wave packets is the size of particles, and the group velocity of wave packets is the running speed of electrons, resulting in interference phenomenon, which is Schrodinger's early insistence. However, this view has also encountered very serious difficulties, because after strict calculation, with the passage of time, the material wave packet of a single particle will inevitably spread, that is, the particle will become fatter and fatter, which is obviously contrary to the experimental results, because all the single electrons we observed in the experiment are localized in a small area of space and are granular. Moreover, if the electron is a material wave packet in three-dimensional space, then in the electron diffraction experiment, the electron wave collides with the crystal and diffracts, and we will see some electrons in different directions in space, which is seriously contradictory to the experiment. All we observe are complete electrons one after another. Understanding electrons as pure fluctuations exaggerates the fluctuation side and obliterates the particle side, which is also a one-sided misunderstanding.
1926, Max Bonn, one of the founders of quantum theory, put forward the statistical explanation of wave function for the first time in his paper Quantum Mechanics of Collision Process [6], which solved this problem and was confirmed by numerous experiments. Bonn won the Nobel Prize in Physics for this. According to the statistical explanation of wave function, the fluctuation of electrons is not a physical wave in real three-dimensional space, but an abstract probability wave. Mathematically, waves describing particles are expressed by a function called wave function. Describing the wave function of particles actually describes the probability distribution of particles in space. When an electron passes through a double slit, the probability wave is coherently superimposed on itself, showing fluctuations, and then interference fringes are produced. When the electron reaches the screen, we observe it, and the wave function of the electron collapses randomly at once, and then a small bright spot appears on the screen, which is characterized by particles. Although the appearance of an electron is random, a large number of electrons conform to the probability distribution, so when a large number of electrons appear, interference fringes are formed.
How do electrons track from the launch to the double slit and then to the final screen? Professor Peter Coveney replied: "If quantum mechanics gives the most basic description, it is meaningless to ask about the whereabouts of electrons unless they have hit the screen. Therefore, we have to come to the conclusion that the electron diffuses in space-time in some way, it passes through two slits and interferes with itself until it finally miraculously collapses to a certain point on the screen, which is completely random. Therefore, we can say that electrons are everywhere, and they are everywhere. " [7]
Electrons are everywhere, which means that it has the probability of distribution in the whole space (the whole universe). Even the distant Andromeda galaxy still has a probability distribution, but the probability value is very small. Electrons are everywhere, that is to say, although it has the probability of being distributed in the whole space, it does not appear in any spatial position (space here refers to physical space), unless the wave function of electrons is observed to make it collapse to a specific spatial position and make it appear. Once the electron collapses, its different distribution probability values in other spatial positions in the whole space range will become zero in an instant, and even the probability distribution value of the distant Andromeda galaxy will become zero in an instant.
Fluctuation in classical physics refers to the periodic continuous propagation process of a real physical quantity through a medium in space, which can produce coherent superposition phenomenon. The characteristics of fluctuation are described by physical quantities such as amplitude, frequency and wavelength. The dispersion of classical waves is spatially distributed. One wave passes through a place, and another wave can also pass through a place. Two waves can be coherently superimposed in the same place, and waves can enter. Particles in classical physics are discrete objects that appear in space. This object has definite position, mass, charge, momentum, etc. And there is a definite continuous orbit in time and space. Classical particles are concentrated in a certain regional space as a whole. If a particle is somewhere, it can't be occupied by another particle at the same time, and other particles can't be occupied. Particles are not. The characteristics of particle motion are described by physical quantities such as momentum, mass, density and particle geometry. In traditional classical physics, volatility and particles are completely opposite. One is scattered and the other is concentrated; A continuous, a separate; One can be superimposed and the other can't be superimposed. They can't exist in one object.
What exactly is an electron? It is neither a classical particle nor a classical wave, but we can say that it is the unity of the duality contradiction between particle and wave, which is the duality of wave and particle. Electron is not a classical particle because it has no continuous orbit determined by classical particles and its discontinuous transition in space. Quantum particles retain the particle size (discreteness, discreteness) of classical particles. Electrons are not classical waves, because they are not real physical waves, but abstract probability waves. Quantum waves retain the coherent superposition of classical waves. After pointing out some common misunderstandings of wave-particle duality, H. Margenau also said: "An electron is neither a particle nor a wave. According to the most widely held view today, which is in harmony with the established theoretical program of quantum mechanics, an electron is an abstract thing, and it can no longer be intuitively understood in the familiar way of daily experience. " [9] For wave-particle duality, we should try to avoid using intuitive images to imagine, because any intuitive image comes from the classical understanding of experience, and sticking to the classical understanding will definitely misinterpret the wave-particle duality. To truly understand wave-particle duality, we must completely abandon the conceptual constraints of classical physics and empirical understanding.
When we are not observing, the electron is an uncertain quantum superposition state, which is described by wave function, which is a probability distribution in the whole space, so it is a probability wave. In fact, the wave function of the whole space is a completely abstract particle. When we observe the wave function of electrons, the whole wave function of all-space electrons collapses randomly into a single specific particle in local space. The superposition of electrons seems to mean that it can be in many places at the same time, everywhere, but everywhere. However, we have never experienced this strange quantum superposition state. Any macroscopic object and self we see can only be in one place in space, not in Beijing or Shanghai.
The explanation of wave-particle duality is in serious conflict with our daily experience and law of excluded middle's formal logic. Therefore, the pioneers of quantum mechanics, including physicists such as De Broglie, Schrodinger and Einstein, find it difficult to accept the explanation of the whole quantum theory put forward by Bohr, Heisenberg and Bonn. Einstein and Bohr have been arguing about this for decades, which is the longest, fiercest and most philosophical debate in physics. Although there are different opinions on the explanation of quantum mechanics and experiments have repeatedly proved the correctness of quantum theory, its basic problems are still puzzling. No wonder Bohr said, "Whoever is not surprised by quantum theory will not understand it." Physicist richard feynman also said in a speech at Cornell University, "I think I can safely say that no one really understands quantum mechanics".
Quantum mechanics has gradually become a computing tool. Most physicists think that as long as the theory is practical, why should we understand it? Like an ostrich, bury your head in the sand and don't look at it. This is the explanation of "shut up and forget it" This pragmatic and instrumental shut-up calculation and explanation can't satisfy people like me who like to get to the bottom of it. Now we want to explore the mystery of wave-particle duality, which requires us to talk about von Neumann's shocking understanding: consciousness leads to the collapse of wave function.
References:
1. george johnson. Ten most beautiful physical experiments [J]. On physics teaching. 2009( 18): 24-25.
2. Feynman. Lecture on Physics in Fei Enman (Volume III) [M]. Shanghai Science and Technology Press 20 13
3. Li Xiaoming, Wang Xiaoming. Statistical analysis of electronic interference [J]. American Journal of Physics, 2002.
4. Zhang Wenjie, et al. Visibility and optical path information of interference fringes in atomic interferometer [J]. Physical review letter. 1998, 8 1(26): 5705-5709.
5. Liu Guoming, Liu Guoming. Controllable double-slit electron diffraction [J]. Electronic Science Press, 2002. Journal of New Physics. 20 13, 15.
6. M Born, "Quantum Mechanics of Science", Journal of Physics, 37,863-867.
7. Peter Coveney. The arrow of time-a scientific journey to solve the biggest mystery of time [M]. Hunan Science and Technology Press, 2002.
8. Zhao Guoqiu. Organic unity of wave-particle duality [J]. Journal of WISCO University. 2000 (02): 1-6。
9. Guan Hong. Generation myth: Copenhagen school [M]. Wuhan Publishing House, 2002.
Next:? ※? Detailed demonstration of wave-particle duality of consciousness (4)
The first part: The detailed demonstration of wave-particle duality of consciousness (2)
A complete series of demonstrations of wave-particle duality of consciousness ※
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