The Copenhagen Institute is 100 years old, and the quantum world is still foggy
The “Spirit of Copenhagen” created by Bohr cannot be copied. This is an academic atmosphere that is improved through discussion, perfected through debate, and discussed on an equal footing with close cooperation. It is to promote the development of quantum mechanics during the debate. This is in line with Bohr’s personality and propositions.
Our reporter Wu Changfeng
In 1900, in order to solve the problem of black body radiation, German physicist Planck proposed the “energy quantum” model. At that time, Einstein was 21 years old and had just graduated from university; Bohr was just 15 years old and might still be studying in middle school.
In 1905, Einstein put forward the “light quantum” hypothesis, and successfully explained the photoelectric effect by imagining the light “should be an electromagnetic wave” as light particles. Immediately afterwards, Bohr proposed a quantized atomic structure in 1913, successfully explained the energy level structure and spectrum of the hydrogen atom, and won the Nobel Prize that year.
In 1921, Bohr rejected the job offer of his teacher Rutherford and decided to establish the Institute of Theoretical Physics of the University of Copenhagen to continue his in-depth study of quantum mechanics. As soon as the institute was established, Bohr’s personality charm quickly became like a magnetic field, attracting a large number of outstanding young physicists. Quantum mechanics such as Heisenberg, Pauli, Born, and Dirac all came from this institute. , Formed the world-famous “Copenhagen School”. In addition to Bohr, this institute has produced 9 Nobel Prize winners in physics, which is unprecedented. Up to now, 100 years have passed, Copenhagen is still the “sacred place of worship” for physicists.
“Does God roll the dice?”
The Copenhagen School began to think about quantum problems from a philosophical level when it was founded. What does the “wave-particle duality” mean when light and electrons sometimes look like waves and sometimes like particles? What is its origin? Why do we only see it as a wave or “one side” of a particle every time? Finally, the “Copenhagen Interpretation” of quantum mechanics surfaced:
——The quantum state of a quantum system can be completely expressed by wave functions. The wave function represents all the information an observer knows about the quantum system, and the description of the quantum system is probabilistic.
――In a quantum system, the position and momentum of a particle cannot be determined at the same time.
-Matter has wave-particle duality. An experiment can show the particle behavior or wave behavior of matter. But it cannot show both behaviors at the same time.
――The measuring instrument is a classic instrument and can only measure classic properties, such as position and momentum.
-The quantum physical behavior of a large-scale macroscopic system should be similar to the classical behavior.
The Copenhagen School’s “probabilistic interpretation” of quantum mechanics, its core view is “measurement collapse”. For a quantum-scale object, its current state is actually a “probabilistic superposition” of several possible states; we cannot predict the true state of the object at all before it is measured. This is a kind of true randomness; once it is activated After the measurement, the object will “collapse” into a possible state, as if it had always been that state.
Although “probability interpretation” is similar to “dice experiment”, quantum mechanics is more pure. The randomness of the dice is actually pseudo-random, and the “Master of Thousands” can completely control the result of the dice. However, the Copenhagen School believes that back to the microscopic quantum world, even the most absurd facts may appear in the quantum world.
Thus, the famous controversy in the history of science kicked off. The classic party led by Einstein launched a fierce attack on the Copenhagen School, and every tit-for-tat gleamed with a spark of wisdom and even art.
Einstein: God does not roll the dice!
Bohr: Please don’t tell God what to do!
This classic dialogue is the beginning of this controversy and the core of subsequent disputes.
Schrödinger, who was on the same front with Einstein, gave an example that he believed to be “extremely absurd” in order to refute the theory of “probabilistic interpretation”: putting a cat together with a set of poison release systems driven by radioactive elements. In the box, before opening the box for observation, the cat is in the superposition of the dual states of “alive” and “poisoned to death” at the same time. This is the famous “Schrodinger’s Cat”.
It is worth mentioning that Schrödinger certainly did not expect that the experiment he proposed to refute the Copenhagen Doctrine, which was considered absurd and incompatible with reality, was mistaken for many people as a classic argument for “probability interpretation”.
It is generally believed that what one person has not achieved in science will surely be replaced by another person in the future. But the “Spirit of Copenhagen” created by Bohr cannot be copied. This is an academic atmosphere that is improved through discussion, perfected through debate, and discussed on an equal footing with close cooperation. It is to promote the development of quantum mechanics during the debate. This is in line with Bohr’s personality and propositions.
Today, many years have passed since the controversy of the century, and the Copenhagen School’s “probabilistic interpretation” doctrine, which is the most widely recognized in the physics world, still faces many controversies.
Although Bohr and Einstein had been arguing all their lives, they did not affect their friendship in the slightest. No matter who leaves who, this quantum galaxy will become bleak.
“No one really understands quantum mechanics”
In the book “Physics and Philosophy: Revolutions in Modern Science” published in 1958, Werner Heisenberg described how he continued to confront Niels Bohr after those long night talks. I said: “Is it possible that nature is so absurd?” Because the quantum world seems so unreasonable and so counter-intuitive, that Richard Feynman said the famous saying: ” No one really understands quantum mechanics.”
Although quantum mechanics has proven its predictive power time and time again, this does not weaken the fact that in addition to the Copenhagen interpretation, the scientific community has many interpretations of quantum theory.
The multi-world interpretation believes that the wave function is physically real, and the Schrodinger equation is precisely a description of reality. When you measure superimposed particles that are in different positions at the same time, the measured particles actually appear in all those positions in different versions of reality. In other words, this means that the two “realities” you are in diverged into two different branches.It sounds like, if you do something bad in this reality
Decide, don’t worry, maybe in another reality, you can still get a perfect result. The multi-world interpretation is also one that is often borrowed from popular culture. The multi-world interpretation poses a problem-it makes probability meaningless.
In order to solve the problem of probabilistic interpretation of multiple worlds, some scientists have developed cosmological interpretations. This interpretation believes that if there are infinite universes, then the multi-world interpretation must be true, because there are infinite “you” undergoing experiments, and reality will be divided in proportion to the probability. In this way, the classical probability still has meaning.
Scientists have also put forward the conjecture of “hidden variables”: perhaps the properties of particles have some “secret” variables, which are actually a certain state, but we don’t know it, and we won’t find it until we measure it.
Scientists put forward the “non-localized hidden variable theory” on the basis of the hidden variable theory, which is the De Broglie-Bohm interpretation. This interpretation believes that particles are real, and they move under the guidance of guided waves that we can’t see.
In addition, there are quantum Bayesianism, quantum Darwinism, transactional interpretation, relational interpretation, etc. Many physicists have put forward different ideas and viewpoints. But some scientists therefore believe that the emergence of so many different interpretations just means that there are still some very basic and fundamental parts of quantum mechanics waiting to be discovered.
“Multiple worlds” and “multiple histories”
The above-mentioned various interpretations of quantum mechanics have been put forward. The core ideas are essentially derived from the multi-world interpretations with concise logic and profound physical implications, but the images are very counter-intuitive. The multi-world theory expresses “one wave function, multiple worlds”, and the various interpretations developed by it are mostly based on self-consistent history, talking about “one world, multiple histories”, but their respective points of focus Different from the focus.
Due to improper interpretation and misrepresentation, the multi-world interpretation has been stigmatized for a long time. Especially at present, many people think that the Copenhagen interpretation is correct, while the multi-world interpretation is regarded as metaphysics or even pseudoscience.
It is precisely because the Copenhagen interpretation of quantum mechanics emphasizes that it must rely on the classical world, which is not logically self-consistent. From a philosophical point of view, the Copenhagen version of quantum mechanics is a kind of dualism, and an ideal perfect theory should be monism: everything comes from quantum, and the classics are just “derivative” phenomena under the macroscopic limit of the quantum system.
In any case, by introducing unobservable properties into physics, physics becomes metaphysics. The most urgent task is to find a measurable and verifiable explanation for the wave function, and observations will not cause the wave function to collapse.
Quantum mechanics has brought changes to the world in many fields. From the first transistor to today’s technological society, to a quantum computer that may become a reality in the near future. It does not matter that we cannot fully understand it, because physicists themselves cannot fully understand it. What we can do is to follow Feynman’s advice, “relax and enjoy”, and then look forward to the birth of “new physics”, opening a new chapter in the exploration of the world and the universe.