2 weeks, 2 days ago



If we talk about the most brilliant debate in human history, it is the century debate between Einstein and Bohr. 

In 1927, the fifth Solvay conference was held in Brussels, Belgium. The theme of this conference was "electrons and photons". In addition to a few scientists such as Sommerfeld and yordang, the most famous scientists in the world all attended the conference, leaving the century photo of "physics all star dream team" which claimed to gather half of human wisdom. 




Four days ago, Einstein did not speak. Even if Bohr, born and Heisenberg joined Schrodinger on the third day, like "three Britain and Lubu", Einstein was still as stable as a mountain. On the afternoon of the fifth day, the great gods began to come to the stage to make concluding remarks. Lorenz called Bohr to speak. Bohr reiterated his Copenhagen interpretation that it was meaningless to discuss where the electron was before measuring its position. In other words, there is no "objective reality" in the physical world. It is boring for physicists to discuss "essence". 

Let's see, because of the emergence of quantum mechanics, there are subtle ripples in the original stable and real space-time, and the world becomes fuzzy and uncertain. Can scientists be so determined by the faltering law of cause and effect, the basis of classical physics? 




Einstein, who had been as strong as a rock under the stage, could not sit down at last: "what? Copenhagen school is just a bunch of prodigies! Physicists just want to go deep into the reason of everything and not discuss the nature of the world. What else do they study? " 

He strode up to the platform, drew an electron through the hole on the blackboard, and got the diffraction image on the screen. 

According to Copenhagen explanation: after the electron passes through the hole, it rushes to the screen with a probability wave. Any point on the screen may become its foothold. After observation, it is found that the electron falls at point a, which is "wave function collapse"! The problem is that other points on the screen should respond to the observation of electrons at the same time, which seems to imply a kind of over distance effect, which also violates the "principle of constant speed of light" in relativity! 




Bohr shook his head, and the two protagonists came to the front desk, from which the debate of the century began. From the meeting place to the dining table and the room, they launched PK at any time. Einstein, who believed in the law of cause and effect, thought: "God doesn't roll dice!" And Bohr's philosophy is, "you don't command what God does. The task of physics is not to find out what nature is, but what we can say about it. " 

Who could have thought that Einstein, who was determined to win, would fail again and again. In the eyes of many physicists who believe in empirical evidence, Bohr's Copenhagen interpretation is the scientific attitude of "know what you know, don't know what you don't know". But Einstein, who was the most rebellious and revolutionary in the field of physics at that time, stood on the opposite side of the new quantum mechanics and became the synonym of conservative. Ellen foster even said angrily, "Einstein, I blush for you! You have put yourself in the same position as those who have been futile in overthrowing relativity! " 




In the next few years, Einstein made a comeback, using "light box experiment" and "EPR paradox" to put pressure on Bohr in turn, and Bohr dissolved them one by one. (of course, Einstein didn't think that he lost the "EPR paradox". This problem didn't really get solved until 50 years later. That's what we'll say later.) 

Seeing that Einstein was about to lose Mecheng, Schr? Dinger stepped forward and wrote to Einstein, in which he conceived such an experiment of thought:

A cat is locked in a closed box. The life and death of a cat depends on the state of a radioactive atom. Within a certain period of time, the atom has a 50% chance to decay. The decay reaction will be observed by the Geiger counter, and a hammer will be released through the relay to break a small bottle of hydrocyanic acid, and the cat will die. 

According to Copenhagen, the quantum system is always in a superposition state before being observed, so the cat is in a "dead and alive" state before opening the box. The thought experiment, which transcends ordinary people's daily experience, is called "Schrodinger's cat" by later generations and ranks among the four great beasts of physics! 




The reason why "Schrodinger's cat" has a profound influence is that Schrodinger used his superhuman wisdom to enlarge the micro quantum effect into our daily world. If the Copenhagen School continues to talk hard, they will have to say, "it is true that before opening the box, the cat was indeed" dead and alive! " 

After receiving Schrodinger's letter, Einstein was overjoyed. He immediately replied to Schrodinger: "if only one person is honest, that person is you (except Laue), because you know you can't avoid reality. Other people don't know what kind of adventure game they're playing at all, (they have to understand), reality is based on experiments! " 

After that, Einstein even mocked the Copenhagen School: "does this mean that when I don't look at the moon, the moon doesn't exist?" 




Scientists in Copenhagen seem to have encountered the biggest crisis. Schr? Dinger pushed them to the forefront with a cat. At the same time, the research on quantum mechanics is not only limited to the physical meaning of the micro world, but also to the daily phenomenon of the macro world, and even to the height of Philosophy. 

Wang Yangming, a great Chinese philosopher, said something similar to Einstein's: "when you don't see the flower, it will go to silence with your heart?" Archbishop Berkeley also said that "being is being perceived". In the past, scientists only regarded this as the idealistic dream in philosophy, and the scientific research should be the "demonstrable" real world. Now, according to Copenhagen's explanation, how our universe should be depends on our observation. Are we in a "idealistic" world? 




"Schrodinger's cat" can't escape the vision of science fiction writers. Liu Cixin's "spherical lightning" is the most unrestrained one among them. In Liu's works, the spherical lightning is actually the macro electron in the "macro world" which is a higher level than our world. It can enter through the wall because of its quantum effect. When people, animals and other objects are hit by the spherical lightning, they become a pool of ashes on the surface, which is actually a quantum superposition state, dispersing in space. Occasionally they still exist in our world, but as soon as they are observed, they disappear immediately, which seems to be the "ghost". 

Liu's imagination really developed the paradox of "Schrodinger's cat" to the extreme! 




Schr? Dinger always wanted to talk to Bohr about cats. Unfortunately, World War II broke out and Schr? Dinger was forced to move to Ireland. Here he wrote "what is life? 》That gave birth to molecular biology. In 1952, he gave a speech in Dublin about his cat and jokingly warned his audience that what he was about to say might "look crazy.". According to him, "Schrodinger equation" describes several different histories, which "happen at the same time". 

It turns out that it was Xue Dashen who first proposed the idea of "multi world". 




The second year after Schr? Dinger's speech in Dublin, a young man graduated from the Department of chemistry entered the Mathematics Department of Princeton University to study military game theory. Soon, he became interested in theoretical physics. At the same time, he studied mathematical physics methods with Wigner (the Nobel Prize for physics in 1963), completed the thesis of Military game theory, and obtained a master's degree. When he was a doctor, he found that he had finally found his own interest, so he abandoned Wigner and devoted himself to studying the basic principles of quantum mechanics under Wheeler gate. 

His classmates said of him: "he is so clever! From chemical engineering to mathematics to physics, in fact, he has been reading science fiction all day. I want to say that's talent. " 

This gifted young man is called Hugh Everett. Because his father and grandfather have the same name: Hugh, we can also call him "Everett III". 




In 1956, Everett compiled his doctoral research into a long paper, wave mechanics without probability, in which he proposed a revolutionary point of view. He believed that The counterintuitive setting of "wave function collapse" should be cut off by "Okam razor". It's better to admit the objective existence of wave function. The reason why we encounter the paradox of "Schrodinger's cat" is that at this time "split" into multiple universes. In some universes, the cat is dead, and in some universes, the cat is still alive. After the two universes "split" (please note the words here: "split"), they are isolated from each other and never meet again, so they can be regarded as "parallel". Therefore, Everett's "multi universe" is also known as "parallel universe". In other places, there have been multiple universes. They all mean the same thing. 




With "multi universe", it is easier to explain the most mysterious double slit interference experiment in quantum mechanics. 

Double slit interference experiment can be found in every middle school physics textbook. Thomas Young used this famous experiment to prove the fluctuation of light. 

After the development of quantum mechanics, the controversy of wave and particle has been raised again. Some people think that if electrons (or photons) are used to pass through the double slits one by one, will interference fringes be produced? 

You say that the electron is a wave, of course, there should be interference fringes, but the problem is that the electron is obviously one by one

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