The Schrōdinger equation (1) is a linear equation. , Although quantum mechanics has held up to rigorous and thorough experimental testing, many of these experiments are open to different interpretations. 2 The many worlds interpretation (MWI) is a theory within quantum physics intended to explain the fact that the universe contains some non-deterministic events, but the theory itself intends to be fully deterministic. Everett’s theory. But many other interpretations of quantum mechanics exist, and today Copenhagenists have more subtle variants to choose from than the one that Everett once called “a philosophic monstrosity.” Here is an all-too-short run-down on some of them. If the functions This means that the universes branch off for each possibility.[2]. What bothers some people about this interpretation is the random, abrupt change in the wave function, which violates the Schrödinger equation, the very heart of quantum mechanics. {\displaystyle i\hbar {\frac {\partial \Psi }{\partial t}}={\frac {-h}{2m}}\nabla ^{2}\Psi +V(x)\Psi (x)}, The basic meaning of this equation is that a particle, such as an electron, is not just a point-like particle, but also a type of wave. © 2021 Scientific American, a Division of Springer Nature America, Inc. Support our award-winning coverage of advances in science & technology. X Other models, such as the Ghirardi-Rimini-Weber theory, introduce specific modifications to the Schrödinger equation. After we detect it at A or B, we have to represent the particle with a new wave function that conforms with the measurement result. {\displaystyle a{\frac {\hbar }{2}}}, This can further be generalized by stating that, Δ ∂ Consistent Histories  is the operator of Since the set of events corresponding to all projector operators on agiven Hilbert space does not have a Boole… Scientific American is part of Springer Nature, which owns or has commercial relations with thousands of scientific publications (many of them can be found at, Projects in Profusion: A Skeptical Look at 3 Wild Fusion-Energy Schemes. The interpretation presented by Albert Einstein himself, states that the outcome of some random event is predetermined. Or do all those other worlds pop out of existence as mere might-have-beens? As recounted by our December article, The Many Worlds of Hugh Everett by journalist Peter Byrne, 50 years ago the iconoclastic physics student Hugh Everett introduced the idea that quantum physics is incessantly splitting the universe into alternate branches. 2 Quantum mechanics has different interpretations that have tried to make it more tangible. It is all that most physicists ever need. Not so for quantum mechanics, at least in the Bohr interpretation. as well as about his theory and the “Copenhagen Interpretation” he aimed to supplant. According to Max Born (1882–1970), the quantum mechanical wave function Ψ does not have any direct physical meaning, whereas its square πΨπ 2 is a probability [1] Born rule, probability in quantum mechanics. Ψ no comments yet. One of the leading ideas of the modal interpretations isprobabilism: quantum mechanics does not correspond in aone-to-one way to actual reality, but rather provides us with a listof possibilities and their probabilities. Everett argued that this approach was philosophically a mess: it used two contradictory conceptual schemes to describe reality, the quantum one of wave functions and the classical one of us and our apparatus. interpretations of Quantum Mechanics. Another fundamental of quantum mechanics is the Heisenberg uncertainty principle. Subjective Interpretations of Quantum Mechanics. . This interpretation has waves traveling forward and backward in time, setting up standing waves, for example between an emitter of a particle and its subsequent detector. 2 –––, 1995c, “Why modal interpretations of quantum mechanics must abandon classical reasoning about the physical properties,” International Journal of Theoretical Physics, 34: 1302–1312. There is general agreement among quantum physicists as to the experimental results in the field of quantum mechanics and the equations which describe these results. x Title: Decoherence, the measurement problem, and interpretations of quantum mechanics. {\displaystyle \Psi _{1},\Psi _{2},\Psi _{3},...\Psi _{n}} This scheme analyzes sequences of states of a system (which may include the whole universe), to find what questions can be consistently answered about the system, such as “was the particle at A or B at time T?” The measurement problem, however, is not resolved: the question of which histories actually happen remains a matter of probabilities just as with the standard Copenhagenist approach. {\displaystyle X_{1}} P Many interpretations, including the Copenhagen interpretation presented by Niels Bohr and Werner Heisenberg, and in particular, von Neumann-Wigner interpretation, state that the consciousness of the person conducting the test affects its result. ) Copenhagenists can point to decoherence as an explanation of what makes large classical systems different from small quantum systems (in general, large systems decohere much more readily and rapidly than tiny ones). If their individual reality is radically different from what we imagine then surely so too is the reality of the pebbles, people and planets that they make up. This is not an interpretation, but it is an important element of the modern understanding of quantum mechanics. , 2 [ = On the other hand, quantum theory is … The randomness of quantum measurements comes about because we cannot know exactly where a particle started out. In quantum mechanics, the mathematical formalism is very difficult to interpret physically. Interpretations of Quantum Mechanics In some respects the decision between a Copenhagenist and an Everettian viewpoint boils down to a basic question: Is the wave function real or is it just information? The cat exist both alive and dead states unless the box is opened, but they are within different branches. Another important fact of quantum mechanics is that the electron behaves in a very weird way. The theory was proposed by David Bohm in 1952 (a few years before Everett’s theory), extending a theory of Louis De Broglie’s from 1927. If it is “real”—in some sense the universe really consists of quantum waves propagating around—then one tends to be driven to an Everettian viewpoint; the “collapses” that wave functions must undergo to produce the one reality that we see are too problematic. Interpretation of quantum mechanics by the double solution theory Louis de BROGLIE EDITOR’S NOTE. This interpretation builds upon the probability-wave notion, but brings in a radical new idea called the superposition principle. A. Grib [ Physics -- Uspekhi 56 , 1230 (2013)] An interpretation of quantum mechanics describes the nature of reality in the quantum realm. Steven Weinberg, Lectures on Quantum Mechanics (2nd ed., 2015), Ch. Or are we ultimately made of the quantum waves alone? The Copenhagen interpretation is one of the best ones to date. It explains very well why we see the classical world that we do, and clarifies the requirements to keep quantum effects manifest in the lab. The philosophy of quantum mechanics; the interpretations of quantum mechanics in historical perspective. • 1. [ Or do the waves merely represent how much information we could possess about the state of the world? The components of the resulting superposition are like parallel universes: in one we see outcome A, in another we see outcome B. Download PDF Abstract: Environment-induced decoherence and superselection have been a subject of intensive research over the past two decades, yet their implications for the foundational problems of quantum mechanics, most notably the quantum measurement … What bothers people about this interpretation is its conclusion that we are perpetually dividing into multiple copies, which may have ghastly implications as well as being bizarre. The best way to explain this principle is by showing it mathematically. 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