John Stewart Bell (June 28, 1928 – October 1, 1990) was a physicist who became well known as the originator of Bell's Theorem, regarded by some in the quantum physics community as one of the most important theorems of the 20th century. June 28 is the 179th day of the year (180th in leap years) in the Gregorian Calendar, with 186 days remaining. ... Year 1928 (MCMXXVIII) was a leap year starting on Sunday (link will display full calendar). ... October 1 is the 274th day of the year (275th in leap years) in the Gregorian calendar. ... 1990 (MCMXC) was a common year starting on Monday of the Gregorian calendar. ... ... Bells theorem is the most famous legacy of the late Irish phyisicist John Bell. ... Fig. ...

He was born in Belfast, Northern Ireland, and graduated in experimental physics at the Queen's University of Belfast, in 1948. He went on to do a PhD in Birmingham, specialising in nuclear physics and quantum field theory. His working career started with the British Atomic Energy Agency, in Malvern, Britain, then Harwell Laboratory. After several years he moved to the European Center for Nuclear Research (CERN). Here he worked almost exclusively on theoretical particle physics and on accelerator design, but found time to pursue a major "hobby", investigating the fundamentals of quantum theory. WGS-84 (GPS) Coordinates: 54. ... Motto:  (Latin for Who will separate us?)[1] Anthem: UK: God Save the Queen Regional: (de facto) Londonderry Air Capital Belfast Largest city Belfast Official language(s) English (de facto), Ulster Scots, Irish3, Northern Ireland Sign Language, Irish Sign Language Government Constitutional monarchy  - Queen Queen Elizabeth II  - Prime Minister of... The Queens University of Belfast (QUB) is a university in Belfast, Northern Ireland; the university is often called Queens University Belfast. ... This article is about the city in England. ... Nuclear physics is the branch of physics concerned with the nucleus of the atom. ... Quantum field theory (QFT) is the application of quantum mechanics to fields. ... Malvern is a town in Worcestershire, England. ... The Atomic Energy Research Establishment near Harwell, Oxfordshire was the main centre for atomic energy research and development in the United Kingdom from the 1940s to the 1990s. ... CERN logo The Organisation Européenne pour la Recherche Nucléaire (English: European Organization for Nuclear Research), commonly known as CERN, pronounced (or in French), is the worlds largest particle physics laboratory, situated just west of Geneva on the border between France and Switzerland. ... Thousands of particles explode from the collision point of two relativistic (100 GeV per nucleon) gold ions in the STAR detector of the Relativistic Heavy Ion Collider. ... A 1960s single stage 2 MeV linear Van de Graaff accelerator, here opened for maintenance A particle accelerator is a device that uses electric fields to propel electrically charged particles to high speeds and magnetic fields to contain them. ...

In 1964, after a year's leave from CERN that he spent at Stanford University, the University of Wisconsin and Brandeis University, he wrote a paper (ref 1 p. 14) entitled "On the Einstein-Podolsky-Rosen paradox". In this work, he showed that the carrying forward EPR's analysis (ref 4) permits one to derive the famous inequality. This inequality, derived from some basic philosophical assumptions, conflicts with the predictions of quantum mechanics. The Leland Stanford Junior University, commonly known as Stanford University (or simply Stanford), is a private university located approximately 37 miles (60 kilometers) southeast of San Francisco and approximately 20 miles northwest of San José in an unincorporated part of Santa Clara County. ... The University of Wisconsin–Madison is a public university located in Madison, Wisconsin. ... Brandeis University is a private university in Waltham, Massachusetts, United States. ... Bells theorem is the most famous legacy of the late Irish phyisicist John Bell. ...

There is some disagreement regarding what Bell's inequality - in conjunction with the EPR paradox - can be said to imply. One camp draws this conclusion: not only local hidden variables, but any and all local theoretical explanations must conflict with quantum theory. Bell himself was in this group: (ref 1 p 196): "It is known that with Bohm's example of EPR correlations, involving particles with spin, there is an irreducible nonlocality." According to a second camp, the correct conclusion is something different. They would say that it is not all possible local theories in general, but only local hidden variables which have shown incompatibility with quantum. Physical theories are said to exhibit nonlocality if it is not possible to treat widely separated systems as independent. ...

Despite the fact that hidden variable schemes are often associated with the issue of indeterminism, or uncertainty, Bell was instead concerned with the fact that orthodox quantum mechanics is a subjective theory, and the concept of 'measurement' figures prominently in its formulation. It was not that Bell found 'measurement' unacceptable in itself, but he objected to its appearance at quantum mechanics' most fundamental theoretical level - which he insisted must be concerned only with sharply-defined mathematical quantities and unambiguous physical concepts. The Copenhagen interpretation is an interpretation of quantum mechanics formulated by Niels Bohr and Werner Heisenberg while collaborating in Copenhagen around 1927. ...

Bell's own words: (ref 1, p. 117) "The concept of 'measurement' becomes so fuzzy on reflection that it is quite surprising to have it appearing in physical theory at the most fundamental level... ...does not any analysis of measurement require concepts more fundamental then measurement? And should not the fundamental theory be about these more fundamental concepts?"

Bell was impressed that within Bohm’s hidden variables theory, reference to this concept was not needed, and it was this which sparked his interest in the field of research. David Bohm. ...

But if he were to thoroughly explore the viability of Bohm's theory, Bell needed to answer the challenge of the so-called 'impossibility proofs' against hidden variables. Bell addressed these in a paper entitled 'On the problem of hidden variables in quantum mechanics' (ref 1 p.1). Here he showed that von Neumann’s argument does not prove impossibility, as it claims. The argument fails in this regard due to its reliance on a physically unreasonable assumption. In this same work, Bell showed that a stronger effort at such a proof (based upon Gleason's theorem) also fails to eliminate the hidden variables program. (Interestingly, the flaw in von Neumann's proof was previously discovered by Grete Hermann in 1935, but did not become common knowledge until rediscovered by Bell.) John von Neumann (Margittai Neumann János Lajos) (born December 28, 1903 in Budapest, Austria-Hungary; died February 8, 1957 in Washington D.C., United States) was a Hungarian-born mathematician and polymath who made contributions to quantum physics, functional analysis, set theory, topology, economics, computer science, numerical analysis, hydrodynamics... Gleasons theorem, named after Andrew Gleason, is a mathematical result of particular importance for quantum logic. ... Grete Hermann (1901-1984) was a German mathematician and philosopher. ... 1935 (MCMXXXV) was a common year starting on Tuesday (link will take you to calendar). ...

If these attempts to disprove hidden variables failed, perhaps one can instead regard EPR and Bell's theorem as a success? The answer to this question hinges on which group one follows. According to Bell's camp, quantum mechanics itself has been demonstrated to be irreducibly nonlocal. Therefore, one cannot fault a hidden variables scheme if - as Bohm's does - it includes "superluminal signalling", i.e., nonlocality. Superluminal communication is the term used to describe the hypothetical process by which one might send information at faster-than-light (FTL) speeds. ...

The alternative camp mentioned above would disagree with this conclusion. This group does not assess the EPR/Bell world as having proven the nonlocality of quantum theory. They would claim that by keeping with orthodox quantum and avoiding hidden variables, one retains locality, and they base arguments against hidden variables on this notion.

In 1972 the first of many experiments that have shown a violation of Bell's Inequality was conducted. Again, the meaning of this violation differs according to how one sees things. Bell himself concludes (see p. 132 ref 1): "It now seems that the non-locality is deeply rooted in quantum mechanics itself and will persist in any completion." The alternative camp would tell us that the experiment means the elimination of local hidden variable theories. 1972 (MCMLXXII) was a leap year starting on Saturday. ... 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). ...

Bell remained interested in objective 'observer-free' quantum mechanics. He stressed that at the most fundamental level, physical theories ought not to be concerned with observables, but with 'be-ables': (ref 1 p. 174) "The beables of the theory are those elements which might correspond to elements of reality, to things which exist. Their existence does not depend on 'observation'." He remained impressed with Bohm's hidden variables as an example of such a scheme and he attacked (ref 1 p 92, 133, 181) the more subjective alternatives such as the Copenhagen and Everett "many-worlds" interpretations. The Copenhagen interpretation is an interpretation of quantum mechanics formulated by Niels Bohr and Werner Heisenberg while collaborating in Copenhagen around 1927. ... The many-worlds interpretation of quantum mechanics or MWI, also known as the relative state formulation, theory of the universal wavefunction, many-universes interpretation, Oxford interpretation or just many worlds, is an interpretation of quantum mechanics that claims to resolve all the paradoxes of quantum theory by allowing every possible...

Blue plaque honouring John Bell at the Queen's University of Belfast

Bell seemed to be quite peaceful with the notion that future experiments would continue to agree with quantum mechanics and violate his inequalities. Referring to the Bell test experiments, he remarked: Image File history File linksMetadata Download high-resolution version (2120x2816, 2563 KB) Blue plaque at the Queens University of Belfast for John Stewart Bell I, the creator of this work, hereby grant the permission to copy, distribute and/or modify this document under the terms of the GNU Free... Image File history File linksMetadata Download high-resolution version (2120x2816, 2563 KB) Blue plaque at the Queens University of Belfast for John Stewart Bell I, the creator of this work, hereby grant the permission to copy, distribute and/or modify this document under the terms of the GNU Free... A blue plaque showing information about The Spanish Barn at Torre Abbey in Torquay. ... The Queens University of Belfast (QUB) is a university in Belfast, Northern Ireland; the university is often called Queens University Belfast. ... 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). ...

"It is difficult for me to believe that quantum mechanics, working very well for currently practical set-ups, will nevertheless fail badly with improvements in counter efficiency ..." (Ref 1, page 109)

Some people continue to believe that agreement with Bell's inequalities might yet be saved. They argue that in the future much more precise experiments could reveal that one of the known loopholes, for example the so-called "fair sampling loophole", had been biasing the interpretations. This latter loophole, first publicized by Philip Pearle in 1970 (ref below), is such that increases in counter efficiency decrease the measured quantum correlation, eventually destroying the empirical match with quantum mechanics. Most mainstream physicists are highly skeptical about all these "loopholes", admitting their existence but continuing to believe that Bell's inequalities must fail. Violation of Bells inequality is, as John Bell realised (see Bells theorem), a straightforward consequence of quantum mechanics. ...

Bell died unexpectedly of a cerebral hemorrhage in Belfast in 1990. How can posterity interpret his most famous work - his contribution to the issues raised by EPR?. Some regard him as having demonstrated the failure of local realism (local hidden variables). Bell's own interpretation - as noted above - is that locality itself met its demise. A cerebral hemorrhage is a bleed into the substance of the cerebrum. ...

References

• Bell, John S, Speakable and Unspeakable in Quantum Mechanics, Cambridge University Press 1987
• Pearle, P, Hidden-Variable Example Based upon Data Rejection, Physical Review D, 2, 1418-25 (1970)
• Aczel, Amir D, Entanglement: The greatest mystery in physics, Four Walls Eight Windows, New York, 2001
• Einstein, Podolsky, Rosen Can Quantum Mechanical Description of Physical Reality Be Considered Complete? Phys. Rev. 47, 777 (1935).

See also

• Bell's theorem, published in the mid-1960s
• EPR paradox, a thought experiment by Einstein, Podolsky, and Rosen published in 1935 as an attack on quantum theory
• CHSH Bell test, an application of Bell's theorem
• Quantum mechanical Bell test prediction
• Quantum entanglement
• Local hidden variable theory
• Bell state

Bells theorem is the most famous legacy of the late Irish phyisicist John Bell. ... 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. ... Albert Einstein ( ) (March 14, 1879 – April 18, 1955) was a German-born theoretical physicist who is widely considered one of the greatest physicists of all time. ... 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 – December 18, 1995) was a physicist. ... Introduction The CHSH Bell test is an application of Bells theorem, intended to distinguish between quantum mechanics (QM) and local hidden variable theories. ... To complete the proof of Bells theorem it is necessary to demonstrate that quantum mechanics makes a prediction that violates a Bell inequality. The following is based on section 2 of an encyclopaedia article written by Abner Shimony, one of the authors of the original Clauser, Horne, Shimony and... It has been suggested that Quantum coherence be merged into this article or section. ... In quantum mechanics, a local hidden variable theory is one in which distant events are assumed to have no instantaneous effect on local ones. ... The Bell states are a concept in quantum information science and represent the simplest possible examples of entanglement. ...

External links

• John Bell and the most profound discovery of science (December 1998)