Minority interpretations of quantum mechanics

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There is a diversity of views that propose interpretations of quantum mechanics. They vary in how many physicists accept or reject them. An interpretation of quantum mechanics is a conceptual scheme that proposes to relate the mathematical formalism to the physical phenomena of interest. The present article is about those interpretations which, independently of their intrinsic value, remain today less known, or are simply less debated by the scientific community, for different reasons.

Contents

History

The historical dichotomy between the "orthodox" Copenhagen interpretation and "unorthodox" minority views developed in the 1950s debate surrounding Bohmian mechanics.

During most of the 20th century, collapse theories were clearly the mainstream view, and the question of interpretation of quantum mechanics mostly revolved around how to interpret "collapse". Proponents of either "pilot-wave" (de Broglie-Bohm-like) or "many-worlds" (Everettian) interpretations tend to emphasize how their respective camps were intellectually marginalized throughout 1950s to 1980s. In this (historical) sense, all non-collapse theories are (historically) "minority" interpretations.

The term 'Copenhagen interpretation' suggests some definite set of rules for interpreting the mathematical formalism of quantum mechanics. However, no such text exists, apart from some informal popular lectures by Bohr and Heisenberg, which contradict each other on several important issues. It appears that the term "Copenhagen interpretation", with its more definite sense, was coined by Heisenberg in the 1950s, [1] while criticizing "unorthodox" interpretations such as that of David Bohm. [2] [3] [4] Before the book was released for sale, Heisenberg privately expressed regret for having used the term, due to its suggestion of the existence of other interpretations, that he considered to be "nonsense". [5]

Since the 1990s, there has been a resurgence of interest in non-collapse theories. Interpretations of quantum mechanics now mostly fall into the categories of collapse theories (including the Copenhagen interpretation), hidden variables ("Bohm-like"), many-worlds ("Everettian") and quantum information approaches. While collapse theories continue to be seen as the default or mainstream position, there is no longer any clear dichotomy between "orthodox" and "unorthodox" views. The Stanford Encyclopedia as of 2015 groups interpretations of quantum mechanics into five classes (all of which contain further divisions): "Bohmian mechanics" (pilot-wave theories), [6] "collapse theories", [7] "many-worlds interpretations", [8] "modal interpretations" [9] and "relational interpretations". [10]

Some of the historically relevant approaches to quantum mechanics have now themselves become "minority interpretations", or widely seen as obsolete. In this sense, there is a variety of reasons for why a specific approach may be considered marginal: because it is a very specialized sub-variant of a more widely known class of interpretations, because it is seen as obsolete (in spite of possible historical significance), because it is a very recent suggestion that has not received wide attention, or because it is rejected as flawed.

As a rough guide to a picture of what are the relevant "minority" views, consider the "snapshot" of opinions collected in a poll by Schlosshauer et al. at the 2011 "Quantum Physics and the Nature of Reality" conference of July 2011. [11] The authors reference a similarly informal poll carried out by Max Tegmark at the "Fundamental Problems in Quantum Theory" conference in August 1997. In both polls, the Copenhagen interpretation received the largest number of votes. In Tegmark's poll, many-worlds interpretations came in second place, while in the 2011 poll, many-worlds was at third place (18%), behind quantum information approaches in second place (24%). Other options given as "interpretation of quantum mechanics" in the 2011 poll were: objective collapse theories (9% support), Quantum Bayesianism (6% support) and Relational quantum mechanics (6% support), besides consistent histories, de Broglie–Bohm theory, modal interpretation, ensemble interpretation and transactional interpretation which received no votes.

List of interpretations

Many-worlds

"Everettian" (many-worlds) interpretations as a whole were long a "minority" field in general, but they have grown in popularity. Multiple variants and offshoots of Everett's original proposal exist, which have sometimes developed the basic ideas in contradictory ways. [12] [13] Interpretations of an Everettian type include the following.

Quantum information

Hidden variables

"Bohm-like" (hidden variable) theories as a whole are a "minority view" as compared to Copenhagen-type or many-worlds (Everettian) interpretations.

Collapse theories

Other

Quantum mysticism

Quantum mysticism is a set of metaphysical beliefs and associated practices that seek to relate consciousness, intelligence, spirituality, or mystical worldviews to the ideas of quantum mechanics and its interpretations. Quantum mysticism is considered by most scientists to be pseudoscience or quackery.

Related Research Articles

The Copenhagen interpretation is a collection of views about the meaning of quantum mechanics, stemming from the work of Niels Bohr, Werner Heisenberg, Max Born, and others. While "Copenhagen" refers to the Danish city, the use as an "interpretation" was apparently coined by Heisenberg during the 1950s to refer to ideas developed in the 1925–1927 period, glossing over his disagreements with Bohr. Consequently, there is no definitive historical statement of what the interpretation entails.

<span class="mw-page-title-main">Many-worlds interpretation</span> Interpretation of quantum mechanics

The many-worlds interpretation (MWI) is a philosophical position about how the mathematics used in quantum mechanics relates to physical reality. It asserts that the universal wavefunction is objectively real, and that there is no wave function collapse. This implies that all possible outcomes of quantum measurements are physically realized in some "world" or universe. In contrast to some other interpretations, the evolution of reality as a whole in MWI is rigidly deterministic and local. Many-worlds is also called the relative state formulation or the Everett interpretation, after physicist Hugh Everett, who first proposed it in 1957. Bryce DeWitt popularized the formulation and named it many-worlds in the 1970s.

<span class="mw-page-title-main">Einstein–Podolsky–Rosen paradox</span> Historical critique of quantum mechanics

The Einstein–Podolsky–Rosen (EPR) paradox is a thought experiment proposed by physicists Albert Einstein, Boris Podolsky and Nathan Rosen which argues that the description of physical reality provided by quantum mechanics is incomplete. In a 1935 paper titled "Can Quantum-Mechanical Description of Physical Reality be Considered Complete?", they argued for the existence of "elements of reality" that were not part of quantum theory, and speculated that it should be possible to construct a theory containing these hidden variables. Resolutions of the paradox have important implications for the interpretation of quantum mechanics.

<span class="mw-page-title-main">Schrödinger's cat</span> Thought experiment in quantum mechanics

In quantum mechanics, Schrödinger's cat is a thought experiment, sometimes described as a paradox, of quantum superposition. In the thought experiment, a hypothetical cat may be considered simultaneously both alive and dead, while it is unobserved in a closed box, as a result of its fate being linked to a random subatomic event that may or may not occur. This thought experiment was devised by physicist Erwin Schrödinger in 1935 in a discussion with Albert Einstein to illustrate what Schrödinger saw as the problems of the Copenhagen interpretation of quantum mechanics.

The de Broglie–Bohm theory, also known as the pilot wave theory, Bohmian mechanics, Bohm's interpretation, and the causal interpretation, is an interpretation of quantum mechanics. It postulates that in addition to the wavefunction, an actual configuration of particles exists, even when unobserved. The evolution over time of the configuration of all particles is defined by a guiding equation. The evolution of the wave function over time is given by the Schrödinger equation. The theory is named after Louis de Broglie (1892–1987) and David Bohm (1917–1992).

An interpretation of quantum mechanics is an attempt to explain how the mathematical theory of quantum mechanics might correspond to experienced reality. Although quantum mechanics has held up to rigorous and extremely precise tests in an extraordinarily broad range of experiments, there exist a number of contending schools of thought over their interpretation. These views on interpretation differ on such fundamental questions as whether quantum mechanics is deterministic or stochastic, local or non-local, which elements of quantum mechanics can be considered real, and what the nature of measurement is, among other matters.

<span class="mw-page-title-main">Wigner's friend</span> Thought experiment in theoretical quantum physics

Wigner's friend is a thought experiment in theoretical quantum physics, first published by the Hungarian-American physicist Eugene Wigner in 1961, and further developed by David Deutsch in 1985. The scenario involves an indirect observation of a quantum measurement: An observer observes another observer who performs a quantum measurement on a physical system. The two observers then formulate a statement about the physical system's state after the measurement according to the laws of quantum theory. In the Copenhagen interpretation, the resulting statements of the two observers contradict each other. This reflects a seeming incompatibility of two laws in the Copenhagen interpretation: the deterministic and continuous time evolution of the state of a closed system and the nondeterministic, discontinuous collapse of the state of a system upon measurement. Wigner's friend is therefore directly linked to the measurement problem in quantum mechanics with its famous Schrödinger's cat paradox.

In quantum mechanics, wave function collapse, also called reduction of the state vector, occurs when a wave function—initially in a superposition of several eigenstates—reduces to a single eigenstate due to interaction with the external world. This interaction is called an observation, and is the essence of a measurement in quantum mechanics, which connects the wave function with classical observables such as position and momentum. Collapse is one of the two processes by which quantum systems evolve in time; the other is the continuous evolution governed by the Schrödinger equation.

In philosophy, the philosophy of physics deals with conceptual and interpretational issues in modern physics, many of which overlap with research done by certain kinds of theoretical physicists. Historically, philosophers of physics have engaged with questions such as the nature of space, time, matter and the laws that govern their interactions, as well as the epistemological and ontological basis of the theories used by practicing physicists. The discipline draws upon insights from various areas of philosophy, including metaphysics, epistemology, and philosophy of science, while also engaging with the latest developments in theoretical and experimental physics.

In physics, a hidden-variable theory is a deterministic physical model which seeks to explain the probabilistic nature of quantum mechanics by introducing additional variables.

In quantum mechanics, the measurement problem is the problem of definite outcomes: quantum systems have superpositions but quantum measurements only give one definite result.

<span class="mw-page-title-main">Pilot wave theory</span> One interpretation of quantum mechanics

In theoretical physics, the pilot wave theory, also known as Bohmian mechanics, was the first known example of a hidden-variable theory, presented by Louis de Broglie in 1927. Its more modern version, the de Broglie–Bohm theory, interprets quantum mechanics as a deterministic theory, and avoids issues such as wave–particle duality, instantaneous wave function collapse, and the paradox of Schrödinger's cat by being inherently nonlocal.

The Afshar experiment is a variation of the double-slit experiment in quantum mechanics, devised and carried out by Shahriar Afshar in 2004. In the experiment, light generated by a laser passes through two closely spaced pinholes, and is refocused by a lens so that the image of each pinhole falls on a separate single-photon detector. In addition, a grid of thin wires is placed just before the lens on the dark fringes of an interference pattern.

Objective-collapse theories, also known spontaneous collapse models or dynamical reduction models, are proposed solutions to the measurement problem in quantum mechanics. As with other interpretations of quantum mechanics, they are possible explanations of why and how quantum measurements always give definite outcomes, not a superposition of them as predicted by the Schrödinger equation, and more generally how the classical world emerges from quantum theory. The fundamental idea is that the unitary evolution of the wave function describing the state of a quantum system is approximate. It works well for microscopic systems, but progressively loses its validity when the mass / complexity of the system increases.

Popper's experiment is an experiment proposed by the philosopher Karl Popper to test aspects of the uncertainty principle in quantum mechanics.

Basil J. Hiley, is a British quantum physicist and professor emeritus of the University of London.

Jeffrey Bub is a physicist and philosopher of physics, and Distinguished Professor in the department of philosophy, the Joint Center for Quantum Information and Computer Science, and the Institute for Physical Science and Technology at the University of Maryland, College Park.

<span class="mw-page-title-main">Quantum Bayesianism</span> Interpretation of quantum mechanics

In physics and the philosophy of physics, quantum Bayesianism is a collection of related approaches to the interpretation of quantum mechanics, the most prominent of which is QBism. QBism is an interpretation that takes an agent's actions and experiences as the central concerns of the theory. QBism deals with common questions in the interpretation of quantum theory about the nature of wavefunction superposition, quantum measurement, and entanglement. According to QBism, many, but not all, aspects of the quantum formalism are subjective in nature. For example, in this interpretation, a quantum state is not an element of reality—instead, it represents the degrees of belief an agent has about the possible outcomes of measurements. For this reason, some philosophers of science have deemed QBism a form of anti-realism. The originators of the interpretation disagree with this characterization, proposing instead that the theory more properly aligns with a kind of realism they call "participatory realism", wherein reality consists of more than can be captured by any putative third-person account of it.

The von Neumann–Wigner interpretation, also described as "consciousness causes collapse", is an interpretation of quantum mechanics in which consciousness is postulated to be necessary for the completion of the process of quantum measurement.

Sheldon Goldstein is an American theoretical physicist. He introduced the term "Bohmian mechanics".

References

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