NationMaster - Encyclopedia: Hidden variable theory

In physics, the hidden variable theory is espoused by a minority of physicists who argue that the statistical nature of quantum mechanics indicates that QM is incomplete. Albert Einstein, the most famous proponent of hidden variables, insisted that, "God does not play dice with the Universe." - meaning that he believed [certain] physical behavior of individual particles cannot be explained only through probabilities. The hidden variable theory is only applicable to ensembles of particles, particles linked through some interaction. If hidden variables exist, new physical phenomena beyond quantum mechanics are needed to explain the universe as we know it. Image File history File links Information_icon. ... The first few hydrogen atom electron orbitals shown as cross-sections with color-coded probability density. ... Many famous physicists of the 20th and 21st century are found on the list of recipients of the Nobel Prize in physics. ... Fig. ... A density matrix, or density operator, is used in quantum theory to describe the statistical state of a quantum system. ...

Quantum mechanics is nondeterministic, meaning that it generally does not predict the outcome of any measurement with certainty. Instead, it merely tells us what the probabilities of the outcomes are. This leads to the strange situation where measurements of a certain property done on two identical systems can give different answers. The question naturally arises whether there might be some deeper reality hidden beneath quantum mechanics, to be described by a more fundamental theory that can always predict the outcome of each measurement with certainty. One of the most famous examples (pre-entanglement) is that of radioactive beta decay. If one looks at the emission of one electron, as one atom decays, one can only determine the probability that the electron will emerge during a given period of time. Hidden variables (inside each atom) would be neccesary to determine the precise moment that each atom decays and emits an electron. Quantum entanglement is a quantum mechanical phenomenon in which the quantum states of two or more objects have to be described with reference to each other, even though the individual objects may be spatially separated. ... In nuclear physics, beta decay (sometimes called neutron decay) is a type of radioactive decay in which a beta particle (an electron or a positron) is emitted. ...

In other words, quantum mechanics as it stands might be an incomplete description of reality. Some physicists maintain that underlying the probabalistic nature of the universe is an objective foundation/property - the hidden variable. Most believe, however, that there is no deeper reality in quantum mechanics — experiments have shown hidden variables to be incompatible with observations.

In 1935, Einstein, Podolsky and Rosen wrote a four-page paper called "Can quantum-mechanical description of physical reality be considered complete?"[1] that argued that such a theory was not only possible, but in fact necessary, proposing the EPR Paradox as proof. In 1964, John Bell showed, through his famous theorem with its Bell inequalities, that if hidden variables exist, certain particles would maintain correlations below these inequalities (which he hoped would be violated through experimentation). Another significant obstacle to hidden variable theories is the Kochen-Specker theorem. Einstein redirects here. ... In quantum mechanics, the EPR paradox is a thought experiment which demonstrates that the result of a measurement performed on one part of a quantum system can have an instantaneous effect on the result of a measurement performed on another part, regardless of the distance separating the two parts. ... Nathan Rosen (March 22, 1909 â€“ December 18, 1995) was a physicist. ... In quantum mechanics, the EPR paradox is a thought experiment which challenged long-held ideas about the relation between the observed values of physical quantities and the values that can be accounted for by a physical theory. ... John Bell (left) and Martinus Veltman (right) discussing Physics at CERN John S. Bell (June 28, 1928 â€“ October 1, 1990) was a physicist who became well known as the originator of Bells Theorem, regarded by some in the quantum physics community as one of the most important theorems of... Bells theorem is the most famous legacy of the late Irish phyisicist John Bell. ... Bells theorem is the most famous legacy of the late Irish phyisicist John Bell. ... The Kochen-Specker theorem was invented by Simon Kochen and Ernst Specker in 1967. ...

Physicists such as Alain Aspect and Paul Kwiat have performed experiments that have found violations of these inequalities up 242 standard deviations^[1](excellent scientific certainty), but the hope for a so-called local hidden variable theory is still very much alive. The loopholes in entanglement experiments such as Aspect's are more serious than is generally realised. Alain Aspect is a French physicist. ... In quantum mechanics, Bells Theorem states that a Bell inequality must be obeyed under any local hidden variable theory but can in certain circumstances be violated under quantum mechanics (QM). ... In quantum mechanics, a local hidden variable theory is one in which distant events are assumed to have no instantaneous effect on local ones. ... Violation of Bells inequality is, as John Bell realised (see Bells theorem), a straightforward consequence of quantum mechanics. ... Quantum entanglement is a quantum mechanical phenomenon in which the quantum states of two or more objects have to be described with reference to each other, even though the individual objects may be spatially separated. ...

A hidden-variable theory, with its underlying determinism, which is consistent with quantum mechanics would have to be non-local, maintaining the existence of instantaneous causal relations between physically separated entities. Though the Bell test loopholes may save the validity of hidden variable theory, experiments have been conducted that observe the non-local/superluminal nature of particle entanglement^[2]. The first hidden-variable theory was the pilot wave theory by Louis de Broglie from the late 1920s. The currently best-known hidden-variable theory, the Bohmian mechanics, of the physicist and philosopher David Bohm, created in 1952, is a non-local hidden variable theory. Determinism is the philosophical proposition that every event, including human cognition and action, is causally determined by an unbroken chain of prior occurrences. ... Fig. ... In physics, the principle of locality is that distant objects cannot have direct influence on one another: an object is influenced directly only by its immediate surroundings. ... Violation of Bells inequality is, as John Bell realised (see Bells theorem), a straightforward consequence of quantum mechanics. ... Louis-Victor-Pierre-Raymond, 7th duc de Broglie, generally known as Louis de Broglie (August 15, 1892â€“March 19, 1987), was a French physicist and Nobel Prize laureate. ... The Bohm interpretation of quantum mechanics, sometimes called the Bohmian Mechanics or Ontological interpretation is an interpretation postulated by David Bohm in 1952, which was an extension of the de Broglie-pilot-wave theory of 1927. ... David Bohm. ...

The Bohm interpretation still enjoys a modest popularity among physicists, although most find it theoretically inelegant. However, there is no consensus. What Bohm did, based on an idea originally by de Broglie, was to posit both the quantum particle, e.g. an electron, and a hidden 'guiding wave' that governs its motion. Thus, in this theory electrons are quite clearly particles. When you perform a double-slit experiment (see wave-particle duality), they go through one slit rather than the other. However, their choice of slit is not random but is governed by the guiding wave, resulting in the wave pattern that is observed. Arms of the ducs de Broglie (or, a saltire anchory azure) The title of Duc de Broglie was a French peerage belonging to a family of Piedmontese origin, which emigrated to France in the year 1643. ... Double-slit diffraction and interference pattern The double-slit experiment consists of letting light diffract through two slits producing fringes or wave-like patterns on a screen. ... In physics, wave-particle duality holds that light and matter exhibit properties of both waves and of particles. ...

Such a view contradicts the simple idea of local events that is used in both classical atomism and relativity theory. It points to a more holistic, mutually interpenetrating and interacting view of the world. Indeed Bohm himself stressed the holistic aspect of quantum theory in his later years, when he became interested in the ideas of J. Krishnamurti. The Bohm interpretation (as well as others) has also been the basis of some books which attempt to connect physics with Eastern mysticism and "consciousness". Albert Einsteins theory of relativity is a set of two theories in physics: special relativity and general relativity. ... Holism in science, or Holistic science, is an approach to research that emphasizes the study of complex systems. ... Jiddu Krishnamurti (May 11, 1895 Madanapalle, India - February 17, 1986 Ojai, California) was discovered as a young boy by C.W. Leadbeater in India on the private beach, that was part of the Theosophical headquarters in Adyar in Chennai. ... Eastern Mysticism is a somewhat imprecise term summarizing mystic traditions of the Middle East, India and the Far East, including mystic elements in Gnosticism] Sufism Yoga Vedanta Buddhism Taoism Category: ... Consciousness is a quality of the mind generally regarded to comprise qualities such as subjectivity, self-awareness, sentience, sapience, and the ability to perceive the relationship between oneself and ones environment. ...

The main weakness of Bohm's theory is that it looks contrived — which it is. It was deliberately designed to give predictions which are in all details identical to conventional quantum mechanics. His aim was not to make a serious counterproposal but simply to demonstrate that hidden-variables theories are indeed possible. This was actually a significant breakthrough. His hope was that this could lead to new insights and experiments that would lead beyond the current quantum theories.

Another type of deterministic theory ^[3] was recently introduced by Gerard 't Hooft. This theory is motivated by the problems that are encountered when one tries to formulate a unified theory of quantum gravity. Gerard t Hooft at Harvard University Gerardus (Gerard) t Hooft [ut-hooft] (The prefix â€™t is pronounced as â€˜utâ€™ and stands for â€˜hetâ€™) (born July 5, 1946) is a professor in theoretical physics at Utrecht University, The Netherlands. ...

Most physicists however are of the position that the true theory of the universe is not a hidden variable theory and that particles do not have any extra information which is not present in their quantum mechanics description. These other interpretations of quantum mechanics have their own philosophical issues. A very small number of physicists believe that local realism is correct and that quantum mechanics is ultimately incorrect. In a nontechnical sense, an interpretation of quantum mechanics is an attempt to answer the question: what exactly is quantum mechanics talking about? Quantum mechanics has been very successful in predicting experimental results. ... In physics, the principle of locality is that distant objects cannot have direct influence on one another: an object is influenced directly only by its immediate surroundings. ...

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