# You know, quantum mechanics can be written in three ways?

Every physicist would agree that one of the biggest paradigm shifts of the last century was the shift from classical physics to quantum physics. Quantum mechanics has changed the face of science. It can explain everything. Explain electricity? sure. Explain how birds fly in one direction? sure. Explain gravity? no way. But what we’re talking about today has nothing to do with it. We’re going to talk about a heated debate about how to understand quantum mechanics. < p > < p > quantum mechanics began with Max Planck and found that light is actually composed of particles with fixed energy. Although he later denied his idea, a few years later, Albert Einstein used Planck’s theory to solve another common problem (photoelectric effect). In the next decade, Nils Bohr, Erwin Schrodinger, Werner Heisenberg, Marx born and Paul Dirac established quantum mechanics. In short, quantum mechanics tells us that we can’t use physical quantities such as position to describe the particles such as electrons and protons. For example, electrons have no fixed position. Instead, we describe them in terms of where they might be. Where is it? Which possible location is its real location? Quantum mechanics tells us that electrons are not in a particular position! Only when we measure them do the electrons have a specific position. < / P > < p > now, in order to express the probability that an electron is in a certain position, we introduce a mathematical tool called wave function. Every possible position of an electron is called a state. The wave function gives the probability of the electron in any state. The behavior of the wave function is similar to that of the wave, which also leads to the behavior of particles as waves in some experiments. You may have heard that particles can also be waves, but actually the behavior of waves is determined by the wave function. The wave function seems to solve many problems. However, there is still a lingering problem: measurement. Wave functions tend to spread out over a given period of time (like any normal wave). This means that the possible positions of electrons have changed. But when we measure the position of the electron, we see that it has a fixed position. So what happens to the diffused wave function during position measurement? That’s what we’re going to talk about today: ways to understand the core ideas of quantum mechanics. < / P > < p > first, let’s look at the oldest (and most popular) explanation of quantum mechanics: the Copenhagen explanation. This is a solution provided by the pioneers of quantum mechanics themselves, with the strong support of Niels Bohr. The Copenhagen explanation tells us that when we measure the wave function, except for the probability of a specific state, all the probabilities become zero and the probability of the measured state becomes 1. This ensures that the electron has a fixed position and does not exist anywhere else. The process in which the probability of a particular state changes to 1 and all other probabilities become 0 is called wave function collapse. < / P > < p > now, can we predict which probability becomes one and which goes to zero? No. This is at the heart of the Copenhagen interpretation. We don’t know where and how the wave function collapses. Every possible position described by the wave function has a chance to become a specific position of the electron. The Copenhagen explanation was widely accepted by physicists at that time. Its number one opponent is Albert Einstein, who hates the idea that wave function collapse happens randomly. < / P > < p > in fact, there are some loopholes in the Copenhagen interpretation: one is that collapse must occur instantaneously. Special relativity (another paradigm of the last century) shows us that no relevant event can happen instantaneously. But Copenhagen’s explanation clearly suggests that if the collapse is not instantaneous, there is little chance that electrons will exist elsewhere. < / P > < p > another problem is that information is not conserved during collapse. What happens to the information related to other states? The Copenhagen explanation does not give an answer. < / P > < p > in addition, there is a problem of where collapse actually occurs, which can be described by the characteristics of the thought experiment known as “Friends of Wigner”. This experiment raises the question, where does collapse occur? Maybe when electrons are measured? Or when information from the wave function enters our brain? The Copenhagen explanation does not give a clear answer. < / P > < p > that’s why more and more physicists are finding Copenhagen’s explanation quite inaccurate. It is these reasons that lead to more explanations. We continue with other explanations. < / P > < p > multi world interpretation is the most sci-fi color. It was proposed by Hugh Everett that every possible state described by the wave function actually becomes the real position of the electron after measurement. How could that be possible? We need to know the concept of parallel universes. < / P > < p > the multi world explanation is that when we measure electrons, the measurement results in the decoherence of the wave function. In short, “decoherence” means that the wave functions are separated from each other. We know that when we measure electrons, decoherence does occur, but the next part is pure speculation. The multi world explanation goes on to say that when measurements occur, the universe splits and multiple parallel universes appear. In every new universe, one of these states becomes a new real location. These universes then continue to split, with each measurement accompanied by a split. < / P > < p > now, this explanation has become the gold mine of science fiction, but it can not be confirmed. It requires new universes not to interact, so how can we detect them? < / P > < p > and a counterintuitive hypothesis, many people think this explanation may be incorrect. However, a public opinion survey of quantum physicists shows that 58% of people think this explanation is correct. However, this explanation is still undeniable, which means that we cannot prove whether it is right or wrong. The theory of navigation wave tells us that the wave function is a real wave, called navigation wave. But it doesn’t just describe a particle, it guides it to move. The particle is at the top of the guided wave and is carried away by the guided wave. But, unlike Copenhagen, the position and trajectory of particles are fixed. However, information about the position and trajectory is not available to us, so we can only observe random results. This fundamentally changes the core philosophy of quantum mechanics: it introduces determinism (the ability to give some initial information to predict everything), rather than probability. Of course, this theory tells us that randomness is still common. Although particles have definite properties, we, as experimenters, cannot observe them directly. That’s why the randomness of quantum mechanics suddenly appears in this theory. < / P > < p > but that’s not all. The explanation goes on to say that there is only one wave function in the universe. Each particle is carried by this strange navigation wave. Up to now, navigation wave interpretation seems to be the only credible and intuitive explanation of quantum mechanics. However, this theory also has some loopholes, one of the biggest is hidden variables. In short, hidden variables are information hidden in the wave function that we can’t touch. By contact, I mean that we can’t even reach them in theory (note that I’m oversimplified here). Now, hidden variables are a big “no” in quantum mechanics. As the mathematician von Neumann has shown, any theory containing hidden variables cannot be accurate. However, navigation wave theory requires global hidden variables, which means that hidden variables have the same value throughout the universe because they are part of a large wave function. This explanation attempts to solve the problem of quantum entanglement by using this hidden variable, but this attempt has been abandoned since it is proved that entanglement is independent of any hidden variable. The fact that it is incompatible with special relativity gives Bohr and other pioneers reasons not to accept it. Until now, some people have begun to favor this explanation. The double slit experiment is one of the most famous experiments in physics. In fact, the origin of quantum mechanics is closely related to this experiment. Although the original design was to prove that light is a wave, when we tried to replace light with electrons, we got an amazing result. < / P > < p > some electrons are emitted through a device. Electrons pass through two slits and then they hit the screen behind the slits (see above). What we see on the screen is a pattern that we can only interpret if we think of electrons as waves. The explanation for this phenomenon is that the electron is described by a wave function and behaves like a wave. So when an electron is launched, it has no definite orbit or position. Only the wave function exists, which represents the probability of electrons in various possible states. The < / P > < p > wave function interferes through these slits, resulting in the graphics on the screen. Remember, the electron is measured when it hits the screen, and now it has a definite location. But with the increase of the number of electrons, they begin to show the distribution of wave function. < / P > < p > now, let’s apply our explanation to this phenomenon. We want to know what happens to the wave function when the electron hits the screen. < / P > < p > Copenhagen: this explanation says that as long as the wave function touches the screen, it is measured. The wave function collapses, which means that the electron is in a certain position. The remaining information in the wave function is lost, which is irreversible. < / P > < p > multi world: the multi world explanation tells us that as long as the wave function touches the screen, it will decoherence. Then the whole universe splits into more “branches.”. The position of the electrons is different. The two universes parted ways and never interacted again. < / P > < p > navigation wave: navigation wave interpretation tells us that the electron has a fixed position and path, but we can’t measure it. The wave function carries electrons on top of them, and once they reach the screen, they reach their intended positions. < / P > < p > you may see that we get the same results, but the way to explain what happened is fundamentally different. Which one is right? We’ll talk about it later. Of course, these are not the only explanations. There are many other explanations. Here I describe three of the most prominent examples. However, if you are curious, there are still some things to learn: quantum Bayesian theory, historical view of consistency, quantum Darwinism, stochastic mechanics, von. Neumann Wigner explanation < / P > < p > so what is the correct explanation? The answer is, “we don’t know.”. We need to study these explanations more deeply, conduct more experiments, look for contradictions, verify predictions, and find loopholes. basic