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04 Nov

John Stewart Bell: The Nature of Reality

CERN / ATLAS Particle Collision

CERN / ATLAS Particle Collision
(c) Ars Electronica/Flickr (CC BY-NC-ND 2.0)

On the 4th November 1964, the physicist John S. Bell published a paper called On the Einstein-Podolsky-Rosen paradox. This was an important paper for both philosophy and physics with implications for our understanding of reality and freedom.

When quantum theory was developed in the early 20th century, the philosophical implications troubled some, including Einstein. The “Copenhagen interpretation” put realism in science under threat. Although the “macro” world (people, planets, plates and platypuses) were argued to be real existing things, electrons and other particles were held not to be. The world was therefore divided into the “classical” and the “quantum” worlds, or as John S. Bell later called them, the “speakable” and the “unspeakable”.

In 1935, Einstein published a paper with Nathan Rosen and Boris Podolsky (known collectively as EPR) arguing that quantum mechanics was not a complete theory, but required additional “hidden” variables to preserve realism and locality. “In the vernacular of Einstein: locality meant no instantaneous (“spooky”) action at a distance; realism meant the moon is there even when not being observed.” (wiki)

Bell also argued for realism, thus rejecting the Copenhagen Interpretation. He worked with realist theories such as de Broglie–Bohm theory, but the theory violated the EPR locality criterion. This fact was used to argue that it was on the wrong track, but Bell’s 1964 paper showed that “any serious version of quantum theory (regardless of whether or not it is based on microscopic realism) must violate locality. This means that if nature is governed by the predictions of quantum theory, the ‘locality principle’ is simply wrong, and our world is nonlocal” (American Scientist)

Experiments have since been carried out demonstrating that nature does indeed follow the predictions of quantum theory in the required way. The “conclusion that there are hidden variables implies that, in some spin-correlation experiments, the measured quantum mechanical probabilities should satisfy particular inequalities (Bell-type inequalities). The paradox consists in the fact that quantum probabilities do not satisfy these inequalities. And this paradoxical fact has been confirmed by several laboratory experiments since the 1970s” (IEP).

Thus Bell converted the EPR thought experiment into real experiments, albeit with results that Einstein would have disliked. It suggests that any quantum theory we arrive at will conflict with common sense. (It also has technical implications for technical advances such as quantum cryptography and quantum computing.)

Later, Bell suggested a hypothesis which would resolve the “spooky action” problem without requiring faster-than-light information transfer: super-determinism. Super-determinism states “[t]hat not only is inanimate nature deterministic, but we, the experimenters who imagine we can choose to do one experiment rather than another, are also determined. If so, the difficulty which this experimental result creates disappears” (from The Ghost in the Atom, P.C.W. Davies and J. Brown, ch.3, p.47, quoted here) – in other words, free will is an illusion.

Bell demonstrated that philosophy and physics can usefully interact. In the words of Tim Maudlin (“on the foundations of physics” in 3:am):

In my view, the greatest philosopher of physics in the first half of the 20th century was Einstein and in the second half was John Stewart Bell. So physicists who say that professional philosophers have not made the greatest contributions to foundations of physics are correct. But both Einstein and Bell had philosophical temperaments, and Einstein explicitly complained about physicists who had no grounding in philosophy. The community of people who work in foundations of physics is about evenly divided between members of philosophy departments, members of physics departments and members of math departments. […] A more salient division in contemporary foundations is between those, like myself, who judge that Bell was basically correct in almost everything he wrote and those who think that his theorem does not show much of interest and his complaints about the unprofessional vagueness that infects quantum theory are misplaced.

Bell’s essay “Against ‘measurement'” lists “system, apparatus, environment, microscopic, macroscopic, reversible, irreversible, observable, information, measurement” as terms ubiquitous in quantum theory that cannot be defined precisely. Without precision, concepts and theory cannot hope to be precise either.

John S. Bell died of a stroke in 1990. At the time of his death he was widely believed to be a front runner for the Nobel Prize in Physics. Surprisingly, his abilities in physics were almost lost. Born in Belfast in 1928, he failed to win a scholarship to grammar school and left school at 16. It was when he was working as a laboratory assistant in Queen’s University that his talent was spotted by Professors Karl Emelaus and Robert Sloane, who encouraged him to attend first-year lectures. Bell then enrolled, obtaining two first-class honours degrees at Queen’s followed by a PhD in the University of Birmingham. He then worked at the UK Atomic Energy Research Establishment, before moving to CERN.

Professor Mary Daly, President of the Royal Irish Academy said ‘The Academy wants John Bell to be the best known scientist in Northern Ireland and to be acknowledged as one of the most important scientists in the world’. A number of events are planned for John Bell Day – see the RIA for more information.

Further reading

Michael Nauenberg, John Bell’s Major Contribution to Physics and Philosophy, RIA.

SEP: Bell’s Theorem

IEP: The Einstein-Podolsky-Rosen Argument and the Bell Inequalities

The Information Philosopher: John Stewart Bell.

Help Wanted: Philosopher required to sort out Reality – Philosophy Now. A great straightforward overview, but available to subscribers only.

3:am, “On the Foundations of Physics” (interview with Tim Maudlin)

THE: When philosophy entangles physics

American Scientist: John Bell across Space and Time.

Tim Maudlin, PBS: Why Physics Needs Philosophy

Irish Times: Ireland’s rich history in science deserves acclaim. Opinion: time to give John Bell the recognition he deserves.

RIA: John Bell Day.

Scientia Salon: Quantum mechanics and scientific realism – on the difficulties of creating a realist theory of quantum mechanics.

John Bell: Belfast street to be named after physicist – a street next to Belfast Metropolitan College in the Titanic Quarter will be named Bell’s Theorem Way or Bell’s Theorem Crescent.

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2 thoughts on “John Stewart Bell: The Nature of Reality

  1. Pingback: Whewell’s Gazette: Vol. #22 | Whewell's Ghost

  2. Pingback: Whewell’s Gazette: Vol. #40 | Whewell's Ghost

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