10 interpretations of quantum mechanics

Dozens of interpretations of quantum mechanics have been developed over the years. Most of them try to resolve what happens when an observation or measurement is made in a quantum system. A mathematical formula known as the wave function (or state vector) describes the state of the system in which the measurement is taking place, and multiple possibilities “collapse” into one result. Quantum "interpretation" tries to explain why collapse occurs and whether it happens at all. Some interpretations start by asking whether the wavefunction is physically real or is still something purely mathematical.

Warning: The clippings below do not reflect the subtleties of various interpretations, which have often changed over time by proponents or even authors. We'll just go over them. As cosmologist Max Tegmark wrote, "there is not even a consensus on what to call interpretation."

10. Bohm Mechanics (David Bohm)

She is not very well liked, but she has a lot of fans and deserves attention. Developed in the 1950s by Bohm, who took the early views of Louis de Broglie as a basis, Bohm mechanics describes the flight of particles driven by "pilot waves." These waves tell the particles where to go. This approach is supposed to bring physics back to determinism, ignoring the probabilities that Einstein condemned when he said "God does not play dice." Since experiment rules out "hidden variables" in favor of determinism, Bohm mechanics requires some action at a distance (or nonlocality). Einstein didn't like anything at all. It is also difficult to see how Bohm mechanics can predict any experimental difference between the predictions of standard quantum mechanics. Shortly before his death, Einstein said he was not impressed by Bohm's interpretation. "Too cheap for me, " Einstein wrote in a letter to physicist Max Born.

9. Interpretation of stochastic evolution

This interpretation, perhaps, cannot be strictly called the interpretation of quantum mechanics, since it changes mathematics. In ordinary quantum mechanics, the wave function "evolves", changes over time in a very predictable way. In other words, the odds of different outcomes can change, and you can predict how exactly they will change until you take a measurement. But some physicists have assumed over the years that evolution itself can change in a random (or stochastic) way to cause its own collapse. It is assumed that this collapse occurs very quickly for large (macroscopic) objects and slowly for subatomic particles. Nobel laureate Steven Weinberg is studying this option closely.

8. Quantum Bayesianism (Christopher Fuchs, Carlton Caves, Rudiger Schack)

This interpretation, sometimes referred to as QBism, takes into account Bayesian statistical research that reflects a personality factor in finding results — personal guesswork. From this point of view, the wave function is "personal", representing measurements of individual knowledge of the state of the system, which can be used to predict its future.

7. The Many-Worlds Interpretation (Hugh Everett III)

Ignored for many years since its introduction in 1957, the many-worlds interpretation has gained popularity in the last decade. The interpretation postulates that every time measurements occur, all possible outcomes occur in different ramifications of reality, creating many parallel universes. In fact, Everett thought of it as splitting the observer into clones that see different dimensions. It's weird anyway.

6. Cosmological Interpretation (Anthony Aguirre and Max Tegmark)

Relatively new. The work appeared only in 2010. In principle, Aguirre and Tegmark argue that if the universe is infinite, then the many-worlds interpretation is correct, since there will be an infinite number of parallel universes in which all possible results of measurements of quantum mechanical processes can occur. Aguirre and Tegmark calculated that the results would occur in the same proportions predicted by the possibilities calculated in the framework of quantum mathematics. Thus, "the wave function describes an actual spatial collection of identical quantum systems, and the quantum uncertainty is explained by the inability of the observer to define himself in this collection."

5. Copenhagen Interpretation

The Copenhagen Interpretation was formulated by Niels Bohr in the late 1920s, at the dawn of quantum mechanics (and later embellished by Werner Heisenberg). Bohr believed that measurements give results that can only be described in the usual language of classical physics, so there is no point in wondering what is happening in some invisible "quantum" region. You need to set up your experimental setup to ask a question about the nature of the universe, and the question you ask implies the answer you get. This point of view includes the Heisenberg uncertainty principle, which limits not measurement, but the very nature of reality - both the position of the particle and its speed simply do not exist when the measurement occurs. Dimension selects one of many possibilities (or Heisenberg potential realities). Bohr explained supposed paradoxes, such as the behavior of a particle as waves and waves as a particle, by mutually exclusive but "complementary" aspects of nature.

4. Successive Stories (Robert Griffiths)

First proposed by Griffiths in 1984, the interpretation of successive stories treats classical physics as close to quantum mechanics, and quantum mathematics can calculate the probabilities of large-scale phenomena as well as subatomic ones. Probabilities do not refer to measurement results, but to the physical state of the system. Griffiths emphasizes the "incompatibility" of many possible realities in quantum physics. You can take a photo of a mountain from different angles, he notes, but the photos must be combined to form the whole picture of the real mountain. In quantum physics, you can choose what you measure (say, the speed of a particle or its position), but you cannot combine the two dimensions to make a complete picture of the particle before the measurement. Before measuring, the actual position and momentum simply do not exist. Likewise, there is no real physical state in which Schrödinger's cat is alive and dead at the same time. The fact that the wave function can describe such a state simply means that the wave function is a mathematical construct for calculating the probabilities of a sequence of events or stories. In real life, each sequence of events will tell a sequential story.

3. Quantum Darwinism (Wojciech Zurek)

Similar in some detail to successive stories, Zurek's quantum Darwinism emphasizes the role of decoherence. It is a process by which several possible quantum realities are eliminated as the system interacts with its environment. As molecules or photons bounce off an object, their trajectories record the position of the object; very soon only one trajectory will remain associated with information recorded in the environment. Such natural interactions produce a kind of "natural selection" of properties that are recorded in the environment, in multiple copies available to observers. Thus, the observer can agree on a specific location of macroscopic objects, instead of multiple locations at the same time.

2. Decoherent Stories (Murray Gell-Mann and James Hartle)

A variation of Griffiths' successive stories is the interpretation of Gell-Mann and Hartle (1989), emphasizing decoherence, like Zhurek with quantum Darwinism. But Gell-Mann and Hartl argue that the entire universe can be viewed as a quantum system without an external environment. Thus, decoherence occurs internally, producing what they call "semiclassical domains" - sets of sequential histories that cannot be discerned against the backdrop of the coarse graininess caused by decoherence.

1. Interpretation of Thomas Siegfried

He believes he will call his interpretation hermeneutic. The work is still in progress. The scientist believes that instead of creating an interpretation of quantum mechanics, he will interpret the interpretations that need interpretation.