PH25006 Gravitational Waves - Obituary Rainer Weiss V01 220925

 

Rainer  originally went to MIT to study electrical engineering but moved to physics

Early in the American morning on September 14, 2015, researchers made a discovery that would advance the field of astrophysics and promise to deepen our understanding of the universe.

On holiday in Maine, Rainer Weiss logged on to his computer, saw the news and yelled “My God!” The observatory he helped to build had registered the “chirp” that he had longed for: a faint signal converted into an audible sound representing a cataclysmic crash that rippled through the cosmos. It earned him the Nobel prize in physics.

The Laser Interferometer Gravitational-Wave Observatory (Ligo), with its vast installations nearly two thousand miles apart, had spotted gravitational waves from the last fraction of a second of a ferocious clash of two merging black holes some 1.3 billion years ago. Predicted a hundred years before by Albert Einstein in his general theory of relativity, the waves are ripples in space-time, the four-dimensional “fabric of the universe”, caused by violent events such as supernovas and collisions of neutron stars. Detecting them gives astrophysicists new tools for observing the universe.

Funded by the United States government at a cost of more than $1.1 billion (about £800 million today) and jointly operated by the Massachusetts Institute of Technology (MIT) and the California Institute of Technology (Caltech), Ligo began operating in 2002 after eight years of construction with the goal of perceiving processes that, despite their force, are extraordinarily tiny once their effects arrive on Earth.

“By the time gravitational waves from Ligo’s first detection reached us, the amount of space-time wobbling they generated was 10,000 times smaller than the nucleus of an atom,” the observatory noted.

Einstein came to doubt whether gravitational waves would ever be measured. “It would have been wonderful to watch Einstein’s face had we been able to tell him,” Weiss remarked after the finding was publicly announced in February 2016.

The observation was not only a validation of Einstein’s theory but of the work of Weiss, a German-born American MIT physics professor who was a central figure in the conception and development of Ligo, having designed a laser antenna to detect gravitational waves and built a prototype in 1972.

Feats of design and engineering, the interferometers in Louisiana and Washington state consist of two 2.5 mile-long antennae fitted with laser beams that travel along chambers that extend like arms in an “L” shape. The beams of light reflect off mirrors at the end of the tubes and recombine to generate patterns, allowing scientists to track minuscule changes in length caused by the squeezing and stretching of space-time as gravitational waves reach our planet. Ligo is, according to its operators, akin to the most precise ruler in the world, capable of measuring on scales ten thousand trillion times smaller than a human hair.

Securing significant public funding for such an esoteric venture was predictably tricky. “Everybody thought we were out of our minds,” Weiss recalled.

The sensitive and delicate equipment required extensive upgrades to improve performance and proved vulnerable to external damage. Weiss walked along the chambers and found cracks and other flaws caused by rodents, wasps and black widow spiders.

Ligo evolved into a project involving a thousand people. The 2017 Nobel was awarded to three, for their “decisive contributions” to the observatory and to gravitational wave detection: Weiss received a half share, with the rest allotted to the Caltech physicists Barry Barish and Kip Thorne.

‘It would have been wonderful to watch Einstein’s face,’ he said 

Weiss, Thorne — an affable, Utahborn friend of Stephen Hawking who was the science adviser for the Christopher Nolan film Interstellar — and Ronald Drever, a Scottish scientist described by Weiss as a “scientific Mozart”, were dubbed the original “troika” for their early efforts. Barish, a gifted manager born in Omaha, joined Ligo in the mid-Nineties and guided it to fruition after some turbulence.

Personality clashes were easy to detect. Weiss, a collaborative and pragmatic New Yorker, supported recruiting Drever from the University of Glasgow.

While brilliant, Drever’s propensity for independent thought did not always delight his colleagues. An entrance to his office was bricked up to make it harder for him to bother the group’s secretary and he was forced off the project in 1992 after falling out with Rochus Vogt, the head of Ligo. Drever (obituary, March 18, 2017) later suffered from dementia and died seven months before the Nobel was announced, making him ineligible for the prize.

Rainer “Rai” Weiss was born in Berlin in 1932. His father, Frederick, was a neurologist and a Jewish communist who was abducted by a “Nazi gang”, Weiss said, after speaking out against Nazis at his hospital. He was released after lobbying by Rainer’s mother, Gertrude Loesner, an actress and a Protestant.

The family then moved to Prague.

On holiday in a hotel in the Tatras in 1938, they adjusted the dials on an old wooden radio to hear Neville Chamberlain’s voice clearly after the Munich Agreement was signed. Realising the ominous implications for Czechoslovakia, the family emigrated to the US in January 1939.

They settled in New York City, where Rainer pursued his passions for music and tinkering with gadgets, combining the two by acquiring cheap military surplus electronic equipment and making and modifying amplifiers, loudspeakers, ham radio transmitters and FM radio receivers.

His father, who became a psychoanalyst and saw patients in the family’s apartment, rebuked him for playing music too loudly. But the teenager was soon invited to build hi-fi sets for his father’s friends. A piano player and a fan of classical music, Weiss grew irked by distortion from scratchy 78 rpm records, a hiss that he found especially bothersome during slow movements while listening to Beethoven. “I started life with one ambition. I wanted to make music easier to hear,” he told the scientist and author Janna Levin.

Aiming to acquire specialist knowledge for his goal of improving sound quality, Weiss enrolled at MIT to study electrical engineering but switched to physics. However, distracted by lovesickness from a failed long-distance relationship with a student in Illinois, he “flunked out” in 1953. He found a way to stay at MIT, securing a role as a technician at the Atomic Beam Laboratory, where a professor, Jerrold Zacharias, took him under his wing. Weiss’s handson electrical skills were valuable as they worked on atomic clocks.

Weiss was allowed to resume his degree then completed a PhD in 1962.

He enjoyed a formative spell at Princeton under the prominent physicist Robert Dicke before returning to MIT as a faculty member, where he started a laboratory focused on cosmology and gravitation. Before long he applied his experimental talents and boyhood interest in instrumentation and background noise reduction to the challenge of gravitational wave detection.

In 1959 he married Rebecca Young, a plant physiologist at Harvard who became a librarian. She survives him with their children, Sarah, an ethnomusicologist, and Benjamin, an art historian and museum curator, and a sister, Sybille, who became a playwright.

Weiss also had a hand in another Nobel-winning endeavour. He chaired the science working group for the Nasa Cosmic Background Explorer project.

The satellite operated from 1989 to 1993 on a mission to map and measure cosmic background radiation. Its findings provided evidence to support the bigbang theory and secured the Nobel prize for physics for two of its scientists.

His turn would come a little over a decade later. The Nobel was one of many prizes awarded to Weiss to mark the fulfilment of a near 50-year quest.

“It’s a spectacular signal,” he told MIT News after the initial detection. “This is the first real evidence that we’ve seen now of high-gravitational field strengths: monstrous things like stars, moving at the velocity of light, smashing into each other and making the geometry of space-time turn into some sort of washing machine.”

Rainer Weiss, Nobel prizewinning physicist, was born on September 29, 1932. He died on August 25, 2025, aged 92

PH25005 Measuring Time V01 200825

Patrick Gill and Helen Margolis at the National Physical Laboratory, Teddington

Next to Europe’s most accurate clock, there is a screw. The screw is, said Rachel Godun, a timing scientist, “the most exciting screw in the lab”.

Probably, metrologists differ in what they view as exciting in screws.

But, still, it is a special screw: the National Physical Laboratory (NPL) in Teddington had to get in surveyors to deduce its precise altitude.

We need that screw because there is no point in being Europe’s most accurate clock if you can’t adjust for the relativistic effect of gravity. As Einstein found out, clocks at different heights run at different rates. So you need to know how high you are.

That’s just the start of the adjustments needed. As NPL works with other laboratories around the world to redefine the second, it even needs to take account of the moon. Every day, tidal forces in the Earth’s crust mean that the screw goes up and down by 50cm. “You have to worry about everything,” said Helen Margolis, head of science for time at NPL.

Such are the considerations required, when your clock is so accurate it would have lost barely a second in the lifetime of the universe.

What, though, is a second? You might think you know. A second is a 60th of a minute, a minute is a 60th of an hour, an hour is a 24th of a day, and a day is how long the Earth takes to rotate.

You would be wrong. That definition hasn’t been right for 60 years. The rotation of the Earth, as a marker of time, is ludicrously inaccurate. It wobbles, it shifts, it changes. Today, a second is instead, 9,192,631,770 oscillations of a microwave beam when tuned to a caesium atom. Much more rational.

If that doesn’t make sense, here is an explanation. To work, clocks need an oscillator. In a grandfather clock, the oscillator is a pendulum. In a traditional atomic clock, it’s a microwave beam.

While a pendulum keeps ticking at the same rate because of gravity, though, the microwave beam is kept regular thanks to quantum mechanics — and a caesium atom. If you hit an atom of caesium just right with a microwave beam, then an electron in the atom moves to a more energetic state.

What the clock does is use that to make sure its microwave beam is always oscillating at a constant, known, frequency. So long as the electron in the atom is moving, the beam is doing what it should. Then by counting the beam oscillations, you know what a second is.

But in this laboratory, and others around the world, they are working on a new, better, definition that they hope to have in place by 2030.

While caesium needs a microwave beam to excite it, the element ytterbium requires a laser beam — and it oscillates a lot faster. Faster oscillations mean you can get more accurate seconds.

So, in a box in their laboratory they have a single ytterbium ion and a laser.

By using it instead of caesium, they reckon they can get a time standard that is 100 times better.

The question is, why? One answer comes in exactly its response to height.

If your clock is so accurate that it is affected by the gravitational effects of relativity, then you could use it to measure those effects.

Slight changes in gravity, or altitude, appear in the time signal — helping with ultraprecise navigation and surveying.

Another reason is because we can.

When, in this same laboratory, Louis Essen invented the first practical atomic clock, no one needed time to be that exact. Today, such clocks have allowed us to probe physics — more accurate ones still would allow us to go further.

Atomic clocks have also allowed us to get around better: satellite navigation simply could not work without them. At the very least more accurate clocks would mean more accurate navigation.

But to redefine the second, we have to agree on what it is. In the world’s top timing laboratories scientists are firing lasers at atoms like ytterbium, and counting how many oscillations a second — a second defined by caesium — keep them excited. Then, once they converge on the same optical frequency, and agree on the atoms to use, the caesium version can be ditched. When it is, when time itself — something humans have always understood by the passage of the sun — is defined instead by ytterbium, what will that mean? What, I ask, even is time? “What is the time? We can do that,” Margolis said. But time itself? “We’re practical, not philosophers. I’m with Einstein: time is what you measure on a clock.” And that’s exactly what she does.

PH25004 Ghost Particles V01 170925

 

A sphere deep beneath a hillside will be bombarded with neutrinos, which will be measured by a global team of scientists

Next image ›

They are sometimes called “ghost particles”, so mysterious are they. And anyone who does not know what subatomic neutrinos are or how they work can feel somewhat reassured: until now, the world’s finest minds have not been quite sure either.

But if Wang Yifang of the Chinese Academy of Sciences, 700 physicist collaborators from around the world and a huge sphere filled with liquid buried deep beneath a lush green hillside get their way, that will soon change.

As of now, 20,000 tonnes of a substance known as a liquid scintillator, contained in the sphere, are being constantly bombarded by neutrinos flowing through the ground from two equidistant nuclear power stations. The sphere itself, a wafer-thin bubble of acrylic, is held within a protective cylinder containing 45,000 tonnes of water.

Bumping into protons in the scintillator, releasing tiny but recordable flashes at a rate of about 50 a day, the neutrinos are being remotely monitored, measured and ranked in mass by global teams of physicists. For neutrinos come in three “flavours”, the nature and hierarchy of which are vital to understanding the building blocks of the universe.

“We are going to know the hierarchy of the neutrino mass,” Wang told The Times, excitedly. “And by knowing this we can build up the model for particle physics, for neutrinos, for cosmology.”

The connection between subatomic particles and the big questions about the nature and history of the universe is well known, if hard to explain. “It’s very much related to our understanding of the universe,” Wang added.

“Soon”, he said, meant six years. That is the time it will take to generate the required 100,000 “flashes” that allow for statistically significant readings. It is satisfyingly precise, and Wang is confident that the experiment cannot fail.

Neutrinos are one of three types of subatomic “building blocks” of matter, the others being quarks, which come in six types, and charged leptons, which also come in three.

Like many discoveries of particle physics, the existence of neutrinos was postulated some years before experimentation proved their existence.

Indeed, Wolfgang Pauli, the Austrian physicist who predicted them in 1930, apologised for his finding, saying: “I have done a terrible thing. I have postulated a particle that cannot be detected.”

He bet a case of champagne that no one would ever detect one. Pauli lost that bet a quarter of a century later. But Wang’s liquid scintillator and the acrylic sphere, which lie at the heart of a facility opened last month in the southern Guangdong province, are an iteration of the same process, designed to prove conclusions that physicists have drawn but have yet to actually observe.

The Jiangmen Underground Neutrino Observatory, or Juno, will allow for controlled measurements of neutrinos that reach it from the two nuclear plants at Yangjiang and Taishan, on the coast. Each is 53km away, and Jiangmen, with its hill, is the perfect site.

Neutrinos flood through the universe from solar and cosmic rays, nuclear fission, and exploding supernova stars unstopped by physical matter.

They pass freely through Earth and indeed the humans living on it — hence the term “ghost particles”.

Pauli thought they had no mass at all, but the discovery that they come in three forms — called electron, muon and tau — has changed that theory.

Analysing how these forms interact — and in particular, how they oscillate from one form to another — should give clues to many of the subatomic world’s greatest secrets, such as the relationship of “matter” to “anti-matter”, and the problem of why there is more matter than its balancing opposite.

That connection to the concept of antimatter, and the cosmological significance of subatomic particles to understanding of black holes and supernovas, or exploding stars, has given a sensationalist edge to research in the field.

When the Cern large hadron collider, the behemoth of particle physics research, opened in 2008 outside Geneva, its scientists had to continually reassure journalists that it wasn’t going to generate a massive black hole that would consume the Earth, or indeed the galaxy. It is probably a good thing that American conspiracy theorists have a lot of other work on their hands at the moment. Jiangmen’s futuristic James Bond-style lair, visited via a passage cut 1,000 metres into the hillside, would be too good to ignore.

But in fact co-operation is the name of the game, rather than the international competition that nowadays most marks China’s relations with the West. Jiangmen is a follow-up to another China-based neutrino project, at Daya Bay, further east in Guangdong, in which American scientists took part. The US is not involved with Jiangmen, but collaborators come from as far afield as Taiwan, Russia, Europe and, in Britain, Warwick University.

After completing its work measuring neutrino oscillations, the facility will be upgraded and put to other uses. Perhaps the most exciting is the possibility of using it to measure a supernova. The Milky Way has not seen a supernova since Chinese astronomers 300 years ago spotted what is thought to have been one, so it is time one appeared.

“In our Milky Way there should be one per 100 years,” Wang said. Given that 99 per cent of a supernova’s energy is transmitted as neutrinos, Juno will have a lot to play with.

PH25003 IOP making publishing Open V01 030825

 Here’s an updated, citation‑rich article exploring how IOP (Institute of Physics & IOP Publishing) is leading the charge to open up physics journal publishing.

1. A Legacy Rooted in Openness 🌐

IOP Publishing launched the first fully open‑access general physics journal—New Journal of Physics (NJP)—in collaboration with the Deutsche Physikalische Gesellschaft in 1998. Since then, it has continued to pioneer open-access physics publishing . NJP remains fully open access under a CC BY license .

2. The Open Physics Programme: Principles in Action

Launched in 2020, Open Physics reflects IOP Publishing’s strategic commitment to openness across three pillars:

• Access: widening researcher reach by offering open access options across all its journals.

• Transparency: implementing transparent and optionally open peer review, transparent metrics and editorial reporting.

• Inclusivity: increasing geographic, gender and institutional diversity across authors and reviewers .

By 2025, IOP had made transparent peer review standard on all hybrid journals, and was assigning DOIs to supplementary data files, supporting FAIR data sharing – a notable step in openness .

3. Scaling Open Access: Progress & Transformative Agreements

➤ Growth in OA Content

• In 2022, 41% of IOP journal output was OA—up from 26% in 2021.

• By 2024, this rose to 47%, representing nearly half of all published articles .

➤ Transformative Agreements

• IOP has signed “read-and-publish” (transformative) agreements with hundreds of institutions across 28 countries by 2023, and expanded to 900 institutions in 33 countries.

• These agreements allow authors at participating institutes to publish papers OA without paying separate author fees .

➤ APC Waivers & Discounts

• IOP offers waivers or discounts on article publication charges for authors from lower‑income countries, with full waivers for Group A countries and 50% discounts for Group B .

4. Domain-Specific Open Access Initiatives

SCOAP³ & Particle Physics

IOPP participates in SCOAP³, an international consortium converting leading high-energy physics journals to fully open access, with author-retained CC BY licensing. NJP, Chinese Physics C and JCAP are among the participant journals .

Journal Launches and Model Flips

• New journal launches include diamond OA and gold‑OA titles (e.g. AI for Science, Journal of Reliability Science and Engineering) with no fees for authors .

• Key publications flipped fully to OA: Applied Physics Express in 2024; Nuclear Fusion in 2023 .

5. Data Sharing & Research Integrity

• Since 2022, IOP has required data availability statements in all articles, and in 2023 mandated explanations if data aren’t shared .

• In 2025, it extended a stronger data-sharing policy to environmental research journals and began assigning DOIs to supplementary data to improve discoverability and FAIR compliance .

6. Leadership in Physics Scholarly Culture

• In March 2025, IOP joined with AIP Publishing and the American Physical Society under the Purpose‑Led Publishing coalition, renewing the commitment to “science first,” and access without compromise on integrity .

• In December 2020, IOP was a key signatory to a joint statement by major physics societies supporting open access, arguing for sustainable models with hybrid and transformative agreements .

7. Real‑World Impact & Outlook

• In 2022, 66% of articles included data‑availability statements, signalling a cultural shift toward transparency .

• Average time from submission to acceptance: ~95 days; from acceptance to online publication: ~18 days .

• New journal titles and series in areas like machine learning, climate/environmental research, and AI reflect high-quality OA expansion .

🔍 Summary Table

Initiative Area Key Highlights

Early Leadership First general physics OA journal (NJP, 1998)

Open Physics Programme Holistic OA strategy: access, transparency, inclusivity

Transformative Agreements Hundreds of institutions, global OA publishing access

APC Support Waivers/discounts for under-resourced authors

Domain Models SCOAP³, OA journal launches, flips of legacy titles

Data & Integrity Policies Mandatory data statements, FAIR policy, transparent review

Strategic Partnerships Purpose‑Led Publishing coalition with APS & AIP

📘 Final Thoughts

IOP is at the vanguard of physics publishing transformation. By combining legacy leadership (like NJP), strategic policies (Open Physics, data sharing, transparent peer review), and global partnerships (transformative agreements, SCOAP³), it is reshaping scholarly communication in physics.

This approach balances author choice and funder mandates, upgrading both the accessibility and integrity of research — while maintaining high standards of peer review and ethical publication.

If you’d like to explore any of these initiatives in depth—such as the SCOAP³ model, data-sharing policies, or transformative agreements—just let me know.

PH25002 Quantum Physics 100 year V01 030825

 The Institute of Physics (IOP) is celebrating the 100 year Anniversary of the discovery of Quantum Physics and still nobody understands it.

www.iop.org/quantum 

www.ioppublishing.org

PH25001 Bell’s Theorem (Quantum Physics) V01 290725

 John Stewart Bell (1928 - 1990) was an Irish physicist and mathematician. He is most well-known for Bell's theorem, an important result in quantum mechanics which can be used to experimentally rule out hidden variables. Bell derived his theorem in 1964 and many experiments have been performed since then which have ruled out hidden variables, thus vindicating quantum mechanics. Bell was born on this day (July 28) in 1928.

Short Biography:-

John Bell's great achievement was that during the 1960s he was able to breathe new and exciting life into the foundations of quantum theory, a topic seemingly exhausted by the outcome of the Bohr-Einstein debate thirty years earlier, and ignored by virtually all those who used quantum theory in the intervening period. Bell was able to show that discussion of such concepts as 'realism', 'determinism' and 'locality' could be sharpened into a rigorous mathematical statement, 'Bell's inequality', which is capable of experimental test. Such tests, steadily increasing in power and precision, have been carried out over the last thirty years.

Indeed, almost wholly due to Bell's pioneering efforts, the subject of quantum foundations, experimental as well as theoretical and conceptual, has became a focus of major interest for scientists from many countries, and has taught us much of fundamental importance, not just about quantum theory, but about the nature of the physical universe.

In addition, and this could scarcely have been predicted even as recently as the mid-1990s, several years after Bell's death, many of the concepts studied by Bell and those who developed his work have formed the basis of the new subject area of quantum information theory, which includes such topics as quantum computing and quantum cryptography. Attention to quantum information theory has increased enormously over the last few years, and the subject seems certain to be one of the most important growth areas of science in the twenty-first century.

John Stewart Bell's parents had both lived in the north of Ireland for several generations. His father was also named John, so John Stewart has always been called Stewart within the family. His mother, Annie, encouraged the children to concentrate on their education, which, she felt, was the key to a fulfilling and dignified life. However, of her four children - John had an elder sister, Ruby, and two younger brothers, David and Robert - only John was able to stay on at school much over fourteen. Their family was not well-off, and at this time there was no universal secondary education, and to move from a background such as that of the Bells to university was exceptionally unusual.

Bell himself was interested in books, and particularly interested in science from an early age. He was extremely successful in his first schools, Ulsterville Avenue and Fane Street, and, at the age of eleven, passed with ease his examination to move to secondary education. Unfortunately the cost of attending one of Belfast's prestigious grammar schools was prohibitive, but enough money was found for Bell to move to the Belfast Technical High School, where a full academic curriculum which qualified him for University entrance was coupled with vocational studies.

Bell then spent a year as a technician in the Physics Department at Queen's University Belfast, where the senior members of staff in the Department, Professor Karl Emeleus and Dr Robert Sloane, were exceptionally helpful, lending Bell books and allowing him to attend the first year lectures. Bell was able to enter the Department as a student in 1945. His progress was extremely successful, and he graduated with First-Class Honours in Experimental Physics in 1948. He was able to spend one more year as a student, in that year achieving a second degree, again with First-Class Honours, this time in Mathematical Physics. In Mathematical Physics, his main teacher was Professor Peter Paul Ewald, famous as one of the founders of X-ray crystallography; Ewald was a refugee from Nazi Germany.

Bell was already thinking deeply about quantum theory, not just how to use it, but its conceptual meaning. In an interview with Jeremy Bernstein, given towards the end of his life and quoted in Bernstein's book [1], Bell reported being perplexed by the usual statement of the Heisenberg uncertainty or indeterminacy principle (ΔxΔp≥ℏ, where Δx and Δp are the uncertainties or indeterminacies, depending on one's philosophical position, in position and momentum respectively, and ℏ is the (reduced) Planck's constant).

At the conclusion of his undergraduate studies Bell would have liked to work for a PhD. He would also have liked to study the conceptual basis of quantum theory more thoroughly. Economic considerations, though, meant that he had to forget about quantum theory, at least for the moment, and get a job, and in 1949 he joined the UK Atomic Research Establishment at Harwell, though he soon moved to the accelerator design group at Malvern.

It was here that he met his future wife, Mary Ross, who came with degrees in mathematics and physics from Scotland. They married in 1954 and had a long and successful marriage. Mary was to stay in accelerator design through her career; towards the end of John's life he returned to problems in accelerator design and he and Mary wrote some papers jointly. Through his career he gained much from discussions with Mary, and when, in 1987, his papers on quantum theory were collected.

Accelerator design was, of course, a relatively new field, and Bell's work at Malvern consisted of tracing the paths of charged particles through accelerators. In these days before computers, this required a rigorous understanding of electromagnetism, and the insight and judgment to make the necessary mathematical simplifications required to make the problem tractable on a mechanical calculator, while retaining the essential features of the physics. Bell's work was masterly.

In 1951 Bell was offered a year's leave of absence to work with Rudolf Peierls, Professor of Physics at Birmingham University. During his time in Birmingham, Bell did work of great importance, producing his version of the celebrated CPT theorem of quantum field theory. This theorem showed that under the combined action of three operators on a physical event: P, the parity operator, which performed a reflection; C, the charge conjugation operator, which replaced particles by anti-particles; and T, which performed a time reversal, the result would be another possible physical event.

Unfortunately Gerhard Lüders and Wolfgang Pauli proved the same theorem a little ahead of Bell, and they received all the credit.

However, Bell added another piece of work and gained a PhD in 1956. He also gained the highly valuable support of Peierls, and when he returned from Birmingham he went to Harwell to join a new group set up to work on theoretical elementary particle physics. He remained at Harwell till 1960, but he and Mary gradually became concerned that Harwell was moving away from fundamental work to more applied areas of physics, and they both moved to CERN, the Centre for European Nuclear Research in Geneva. Here they spent the remainder of their careers.

Bell published around 80 papers in the area of high-energy physics and quantum field theory. Some were fairly closely related to experimental physics programmes at CERN, but most were in general theoretical areas.

The most important work was that of 1969 leading to the Adler-Bell-Jackiw (ABJ) anomaly in quantum field theory. This resulted from joint work of Bell and Ronan Jackiw, which was then clarified by Stephen Adler. They showed that the standard current algebra model contained an ambiguity. Quantisation led to a symmetry breaking of the model. This work solved an outstanding problem in particle physics; theory appeared to predict that the neutral pion could not decay into two photons, but experimentally the decay took place, as explained by ABJ. Over the subsequent thirty years, the study of such anomalies became important in many areas of particle physics. Reinhold Bertlmann, who himself did important work with Bell, has written a book titled Anomalies in Quantum Field Theory [10], and the two surviving members of ABJ, Adler and Jackiw shared the 1988 Dirac Medal of the International Centre for Theoretical Physics in Trieste for their work.

While particle physics and quantum field theory was the work Bell was paid to do, and he made excellent contributions, his great love was for quantum theory, and it is for his work here that he will be remembered. As we have seen, he was concerned about the fundamental meaning of the theory from the time he as an undergraduate, and many of his important arguments had their basis at that time.

Einstein's strongest argument, though this did not become very generally apparent for several decades lay in the famous Einstein-Podolsky-Rosen (EPR) argument of 1935, constructed by Einstein with the assistance of his two younger co-workers, Boris Podolsky and Nathan Rosen. Here, as is usually done, we discuss a simpler version of the argument, thought up somewhat later by David Bohm.

The result of this argument is that at least one of three statements must be true:

(1) The particles must be exchanging information instantaneously i.e. faster than light;

(2) There are hidden variables, so the results of the experiments are pre-ordained; or

(3) Quantum theory is not exactly true in these rather special experiments.

The first possibility may be described as the renunciation of the principle of locality, whereby signals cannot be passed from one particle to another faster than the speed of light. This suggestion was anathema to Einstein. He therefore concluded that if quantum theory was correct, so one ruled out possibility (3), then (2) must be true. In Einstein's terms, quantum theory was not complete but needed to be supplemented by hidden variables.

Bell thus supported realism in the form of hidden variables. He was delighted by the creation in 1952 by David Bohm of a version of quantum theory which included hidden variables, seemingly in defiance of von Neumann's result. 

In 1964, Bell made his own great contributions to quantum theory. First he constructed his own hidden variable account of a measurement of any component of spin. This had the advantage of being much simpler that Bohm's work, and thus much more difficult just to ignore. He then went much further than Bohm by demonstrating quite clearly exactly what was wrong with von Neumann's argument.

Von Neumann had illegitimately extended to his putative hidden variables a result from the variables of quantum theory that the expectation value of 

A+B is equal to the sum of the expectation values of A and of B. (The expectation value of a variable is the mean of the possible experimental results weighted by their probability of occurrence.) Once this mistake was realised, it was clear that hidden variables theories of quantum theory were possible.

However Bell then demonstrated certain unwelcome properties that hidden variable theories must have. Most importantly they must be non-local. He demonstrated this by extending the EPR argument, allowing measurements in each wing of the apparatus of any component of spin, not just s_z . He found that, even when hidden variables are allowed, in some cases the result obtained in one wing must depend on which component of spin is measured in the other; this violates locality. The solution to the EPR problem that Einstein would have liked, rejecting (1) but retaining (2) was illegitimate. Even if one retained (2), as long as one maintained (3) one had also to retain (1).

Bell had shwed rigorously that one could not have local realistic theories of quantum theory.

The other property of hidden variables that Bell demonstrated was that they must be contextual. Except in the simplest cases, the result you obtained when measuring a variable must depend on which other quantities are measured simultaneously. Thus hidden variables cannot be thought of as saying what value a quantity 'has', only what value we will get if we measure it.

Let us return to the locality issue. So it has been assumed that quantum theory is exactly true, but of course this can never be known. John Clauser, Richard Holt, Michael Horne and Abner Shimony adapted Bell's work to give a direct experimental test of local realism. Thus was the famous CHHS-Bell inequality [19], often just called the Bell inequality. In EPR-type experiments, this inequality is obeyed by local hidden variables, but may be violated by other theories, including quantum theory.

Bell has reached what has been called experimental philosophy; results of considerable philosophical importance may be obtained from experiment. The Bell inequalities have been tested over nearly thirty years with increasing sophistication, the experimental tests actually using photons with entangled polarisations, which are mathematically equivalent to the entangled spins discussed above. While many scientists have been involved, a selection of the most important would include Clauser, Alain Aspect and Anton Zeilinger.

While at least one loophole still remains to be closed [in August 2002], it seems virtually certain that local realism is violated, and that quantum theory can predict the results of all the experiments.

For the rest of his life, Bell continued to criticise the usual theories of measurement in quantum theory. Gradually it became at least a little more acceptable to question Bohr and von Neumann, and study of the meaning of quantum theory has become a respectable activity.

Bell himself became a Fellow of the Royal Society as early as 1972, but it was much later before he obtained the awards he deserved. In the last few years of his life he was awarded the Hughes Medal of the Royal Society, the Dirac Medal of the Institute of Physics, and the Heineman Prize of the American Physical Society. Within a fortnight in July 1988 he received honorary degrees from both Queen's and Trinity College Dublin. He was nominated for a Nobel Prize; if he had lived ten years longer he would certainly have received it.

This was not to be. John Bell died suddenly from a stroke on 1st October 1990. Since that date, the amount of interest in his work, and in its application to quantum information theory has been steadily increasing.

Died

1 October 1990

Geneva, Switzerland

Source: Mac Tutor