A single event does not make a law invalid...neutrinos vs speed of light

"Take Heart, Einstein: ‘Earth-Shattering’ Science Is Relatively Rare?"

 
by

Adam Mann

September 26th, 2011

Wired Science

What began last week as whispered rumors posted on the physics blog Resonaances grew to a roar of articles around the world about an experiment that has seen neutrinos traveling faster than the speed of light.

The findings from the Oscillation Project with Emulsion-t Racking Apparatus (OPERA) collaboration at Gran Sasso National Laboratory in Italy show neutrinos arriving 60 nanoseconds sooner than expected, and have many eager sources suggesting the possibility of overturning Einstein’s well-known theory of relativity. While the prospect is exciting, can just one result really upend a century of physics?

“It really depends on what happens next,” said Mordecai-Mark Mac Low, curator of the Division of Physical Sciences at the American Museum of Natural History in New York.

Taking the historical view, Mac Low compares the result to other earth-shattering experiments from recent decades. In 1986, physicists announced the miraculous discovery of a superconducting material that worked at temperatures higher than were thought possible. But it wasn’t until many other experiments confirmed the finding that the original work could be seen as credible.

On the other hand, when an experiment in 1989 seemed to have created the astonishing feat of cold fusion, the findings were ultimately dismissed because no other team could corroborate the results.

“In general, things aren’t turned over by one experiment,” said Rob Plunkett, a physicist at Fermilab National Laboratory in Batavia, Illinois. “The whole process of science is by its nature self checking; one experiment always has to be checked with another.”

Plunkett is in a good position to speak on this, as he is co-spokesperson for the Main Injector Neutrino Oscillation Search (MINOS) experiment, which is one of only a few that can independently verify the original OPERA results. MINOS did in fact see several neutrinos back in 2007 that seemed to be moving faster than light, but dismissed the findings because the margin of error was too high. Still, Plunkett remains skeptical of the OPERA claims and said it would take six to nine months before his collaboration will be able to verify or contradict the findings.

But even if the faster-than-light neutrinos are found to be valid, that doesn’t mean scientists have to toss out their old theories. “Relativity and quantum mechanics didn’t throw away Newton and Maxwell,” said Lawrence Krauss, a physicist at Arizona State University in Tempe, Arizona.

New data can expand our view of the universe, Krauss explained, but it doesn’t automatically invalidate well-tested theories from the past. For instance, when data in 1998 revealed the existence of dark energy and showed that the expansion of the universe was accelerating — a very unexpected result — it merely modified, not destroyed, the theories that came before.

For his part, Krauss also remains fairly unconvinced of the neutrino results. “When an experiment does something that violates everything we think, it’s much more likely that there’s simply a mundane explanation.”

Should have used Heathkit No. 4530949E

There is something to be said about being absolutely sure before a disclosure is announced.

"Faster-than-light neutrinos could be down to bad wiring"

by

Jason Palmer

February 23rd, 2012

BBC News

What might have been the biggest physics story of the past century may instead be down to a faulty connection.

In September 2011, the Opera experiment reported it had seen particles called neutrinos evidently travelling faster than the speed of light.

The team has now found two problems that may have affected their test in opposing ways: one in its timing gear and one in an optical fibre connection.

More tests from May will determine just how they affect measured speeds.

The Opera collaboration (an acronym for Oscillation Project with Emulsion-Racking Apparatus) was initially started to study the tiny particles as they travelled through 730km of rock between a particle accelerator at the European Organization for Nuclear Research (Cern) in Switzerland and the Gran Sasso underground laboratory in Italy.

Its goal was to quantify how often the neutrinos change from one type to another on the journey.

But during the course of the experiments the team found that the neutrinos showed up 60 billionths of a second faster than light would have done over the same distance - a result that runs counter to a century's worth of theoretical and experimental physics.

The team submitted the surprising result to the scientific community in an effort to confirm or refute it, and several other experiments around the world are currently working to replicate the result.

A repeat of the experiment by the Opera team will now address whether the issues they have found affect the ultimate neutrino speed they measure.
Faulty connection?

The two problems the team has identified would have opposing effects on the apparent speed.

On the one hand, the team said there is a problem in the "oscillator" that provides a ticking clock to the experiment in the intervals between the synchronisations of GPS equipment.

This is used to provide start and stop times for the measurement as well as precise distance information.

That problem would increase the measured time of the neutrinos' flight, in turn reducing the surprising faster-than-light effect.

But the team also said they found a problem in the optical fibre connection between the GPS signal and the experiment's main clock - quite simply, a cable not quite fully plugged in.

In contrast, the team said that effect would increase the neutrinos' apparent speed.

The team had carried out their measurements for more than three years, exhaustively scrutinising their methods and analysis before announcing the results last year - so why had they not found these issues before?

"It's sometimes very difficult to tell whether this thing could have been done before - because in a sense the answer is always yes," said Sergio Bertolucci, director of research at Cern.

Prof Bertolucci outlined the complexity both of the experiment and the analysis of the results, stressing that the hunt for just these kinds of problems had been relentless.

"One has to realise that the collaboration has never stopped to try to 'kill' the measurement (proving that it was erroneous)," he told BBC News.

"Their constant search for systematic (errors) has never stopped, for more than a year."

Given that the opposing effects only seem to muddy the waters further on whether neutrinos can exceed the "universal speed limit", only more experiments will put the matter to rest.

For its part, the Opera team said in a statement: "While continuing our investigations, in order to unambiguously quantify the effect on the observed result, the collaboration is looking forward to performing a new measurement of the neutrino velocity as soon as a new bunched beam will be available in 2012."

Facilities also at Gran Sasso called Borexino, LVD and Icarus will also take part, along with Minos, based at Fermilab in the US, and possibly a Japanese facility called T2K.

With so much at stake, Oxford University particle physicist and Minos spokesman Alfons Weber said these international efforts will go ahead no matter what.

"I can say that Minos will quite definitely go ahead," Dr Weber told BBC News. "We've already installed most of the equipment we need to make an accurate measurement.

"Even if Opera now publish that 'Yes, everything is fine', we still want to make sure that we come up with a consistent, independent measurement, and I assume that the other experiments will go forward with this as well."

But Prof Bertolucci at Cern says that there are wider implications of the neutrino story, which is playing out in the public eye.

"All this story has shown to the wider public how science works," he said.

"Of course the people of Opera are not happy; they would have preferred that the neutrinos stayed [faster than light], but the fact that they came out and they put themselves to the scrutiny of the wider collaboration... I think makes a good case for science."

Bruno Pontecorvo...neutrinos and a defector to Russia

Nature has the most recent article on him...got $32?

Bruno Pontecorvo [Wikipedia]

"Bruno Pontecorvo Is Dead at 80; Physicist Defected to Soviet Union"

by

Randy Kennedy

September 28th, 1993

The New York Times

Bruno Pontecorvo, an Italian-born physicist who was a pioneer in the study of the elusive subatomic particles called neutrinos and who defected to the Soviet Union in 1950, died Friday in Dubna, outside Moscow. He was 80.

The cause was pneumonia, according to reports in Italian newspapers. He had suffered from Parkinson's disease for several years.

Mr. Pontecorvo was one of a group of talented young physicists who worked with Enrico Fermi in Rome in the early 1930's on experiments that proved radioactive isotopes of a number of elements can be produced by exposing the elements to neutrons that have been slowed down.

After Mussolini passed laws that discriminated against Jews, Mr. Pontecorvo, who was Jewish, moved to Paris to continue his work. He left for the United States in 1940 after the Nazi invasion. He worked briefly for an American oil company and then moved to Canada, where he applied to become a British citizen.

In 1948, after he completed his naturalization, he moved to England to join the Atomic Energy Research Laboratory at Harwell, near Oxford. Disappearance in Rome

But in the late summer of 1950, Mr. Pontecorvo and his family disappeared during a vacation in Rome. They were last seen in Helsinki on Sept. 2, 1950, and were believed to have taken a ship to the Soviet Union with the help of Soviet diplomats in the Finnish capital. It was not until 1955, when Mr. Pontecorvo published articles in Pravda and Izvestia, that officials were certain he was working in the Soviet Union.

His defection, which came the same year that one of his colleagues, Klaus Fuchs, was convicted of espionage in Britain, raised fears that the Italian scientist had fled with secrets that could be used to help build a hydrogen bomb. Another colleague, Alan Nunn May, was convicted of espionage charges in Canada in 1946.

But in frequent statements to the press in the Soviet Union, and during his first trip back to Italy in 1978, he maintained that his research in Canada and England had no military applications. He said he had defected to pursue nuclear research for peaceful purposes because investigations into scientific espionage had made it too difficult for him to work.

"In 1950, the atmosphere was such that I could no longer breathe," he wrote in the 1955 article in Pravda. In the article, he also said that he had signed a petition along with several other nuclear scientists calling for a worldwide ban on nuclear weapons.

His British citizenship was revoked because it was believed he defected with military secrets, but he was never charged with espionage.

He is known in his field for being one of the first physicists to suggest using a solution containing chlorine to detect neutrinos.

"Confessions of an atom spy: Forty years after Bruno Pontecorvo, a British scientist, went to work for Moscow, he tells Charles Richards in Rome why he changed sides"

by

Charles Richards

August 2nd, 1992

The Independent

He stepped out of the lift on the third floor, entered the room, and smiled. Now 78 and a victim of Parkinson's disease, Bruno Pontecorvo is short and spare, with an old tweed jacket hanging off his drooping shoulders. His pale green eyes, however, still gleam with mischief.

He spends most of his time in Italy these days, but for a year he had fobbed me off, saying over the phone that he was too sick and did not give interviews about the past. Now at last we were meeting at the home of Miriam Mafai, a columnist on the daily La Repubblica who has just published a book about him.

A physicist, Pontecorvo was deeply involved in the British nuclear research programme when, in 1950, he decided during a holiday in Italy that he would abandon the West and make a new life in the Soviet Union. His defection, following closely on the unmasking of the atom spy Klaus Fuchs, a colleague at the government atomic research centre at Harwell, deeply embarrassed the Attlee government. Had Pontecorvo taken with him more atomic bomb secrets? Had he been spying for the Russians all along? He was vilified for treachery and stripped of his adopted British nationality.

Now, for the first time, he is prepared to talk about the choice he made. But, with most Communist countries having changed their colours, how does he feel about the dedication of his life to the Communist cause?

'The simple explanation is this: I was a cretin,' he said. 'The fact that I could be so stupid, and many people close to me should have been quite so stupid . . .' The sentence was left unfinished.

Communism, he went on, was 'like a religion, a revealed religion . . . with myths or rites to explain it. It was the absolute absence of logic.' He stuck by his faith, even after the invasion of Hungary in 1956. When Andrei Sakharov, a fellow physicist, turned against the system, it made no difference. 'I had always admired him as a great scientist and a man of integrity. However, my idea was that he was naive . . . it was I who was naive.'

It was only after Czechoslovakia that his views began to change. 'After 1968 I would say, I will not talk of such things. Then, after a few years, I understood what an idiot I was.'

He speaks clear, idiomatic English. He is a man of immense charm and elegance of language, quoting from Dante, which he read in the Soviet Union to remind himself of Italy.

Born in Pisa in 1913, Pontecorvo was the fourth of eight children of a textile merchant. He showed early academic promise, and in 1934 went to Rome to join an extraordinary circle of world- class physicists led by Enrico Fermi, later to become one of the fathers of the atomic bomb. When Mussolini passed racial laws that discriminated against Jews, four of the Pontecorvos went to Britain. (The eldest, Guido, a distinguished geneticist, remained in Britain and is a Fellow of the Royal Society.)

Bruno went to France and then, in 1940, to the United States. Three years later he was asked to join an Anglo-Canadian team conducting secret research at Montreal. This was Britain's wartime nuclear reactor programme, which was separate from the American-led Manhattan Project working on the first atomic bombs. In 1948, while still working in Canada, Pontecorvo became a British subject. In January 1949 he left with his family to take up a senior post in the Atomic Energy Research Establishment at Harwell, near Oxford. It was not a nuclear weapons plant, although such was the secrecy surrounding its work that it was popularly believed to be.

In the late summer of 1950, Pontecorvo went on holiday to Italy with his family, and disappeared. It was widely assumed that the Pontecorvos flew to Stockholm, spent the night in a building belonging to the Soviet Union, and flew on to Helsinki. Then a Soviet vessel left the city's harbour shortly afterwards.

Two weeks passed before the alarm was raised in Britain, and another sensational security scandal broke over the government's head. How much did Pontecorvo know? Had he been vetted? Had he been in league with Fuchs? As always with these matters, the principal casualty was Britain's standing in Washington, where once again it was exposed as a soft touch for Soviet subversion. Very soon the relevant minister was forced to admit: 'I have no doubt that he is in Russia.'

It was not until 1955 that Pontecorvo surfaced in Moscow, giving a press conference at which he said he had defected to correct the balance between East and West and that he had only ever worked on the peaceful uses of atomic energy. 'I became convinced,' he said, 'that in the Soviet Union the people wanted peace, and that their government was doing everything possible that there should be no war.'

What had prompted him to defect at that moment, who had helped him through the Iron Curtain and how exactly he made that journey, remained a mystery. Now, the first new evidence is emerging. A week ago, an old Italian Communist Party hardliner, Giulio Seniga, said that he had been a member of an underground party network that arranged Pontecorvo's flight to Moscow. And Pontecorvo himself revealed to Miriam Mafai how he crossed the Soviet border. 'We did not go by ship,' he said. 'We went straight to the Soviet embassy, and then we left in two cars, with me locked in the boot.'

But had he spied for Moscow before then? He still does not talk about it. Fuchs himself told the British that he believed someone else, probably at Harwell, was talking to the Russians, and spy writers Christopher Andrew and Oleg Gordievsky are in no doubt that it was Pontecorvo. 'KGB officers,' they have written, 'said that they rated Pontecorvo's work as an atom spy almost as highly as that of Fuchs.'

In 1950, certainly, the press was quick to denounce him, but today the available evidence does not appear to support the suggestion that he was an important atom spy. His research at Harwell had no military application and in Canada he had worked on reactors rather than weapons.

At any rate, Pontecorvo today is not a wanted man. He has been visiting Italy regularly since 1978, although his home remains in Dubna, the research centre outside Moscow where he has been living with his wife and children. He has, he says, a lingering nostalgia for the country whose citizenship he held for a dozen years in the middle of his life, and to which he insists he did no harm. 'I love England, the cathedrals. It is also the least corrupt country.'

For a verdict on the life of Bruno Pontecorvo, there may be no better judge than his brother Gillo, the director who won international acclaim for his film, The Battle of Algiers. 'The case of Bruno was very simple,' he told me. 'Forget all the lies told about it. We were living at a period of great change. There was this belief in a city of the future. The belief was almost irrational, but was held by a whole generation of men, above all intellectuals . . . He had that religion, that sense of capitalism equalling war and recurrent crisis and racism. All that had to be overthrown to go towards the new world. They were like the early Christians, who believed in something beautiful, which did not exist.

'We bet on something which turned out to be false. It is like stepping out of a window, and hoping to descend slowly without taking the boring route of the stairs or the lift. We ignored the problem of the law of gravity.'

Slow down there Mr. Neutrino

"Particles Faster Than the Speed of Light? Not So Fast, Some Say"

by

Dennis Overbye

October 24th, 2011

The New York Times

“Does E still equal MC squared?”

So asks the Irish band the Corrigan Brothers in a new song, “Einstein and the Neutrinos,” that is the latest rollicking riff on news that shocked the scientific world last month.

A group of physicists from Italy claimed they had observed the subatomic particles called neutrinos traveling faster than the speed of light. That, of course, is the cosmic speed limit declared in Albert Einstein’s theory of special relativity in 1905.

If they are right — and the jury is still out — Einstein might have some explaining to do. Among other things, a neutrino or anything else that went faster than the speed of light could go backward in time.

Physicists, who are quite sure that in fact E does still equal MC squared — whatever may come of this experiment — have expressed skepticism. But that has not stopped the ghostly neutrinos, which can sail through miles of solid lead with impunity, from achieving a sort of pop culture fame not seen since 1960, when John Updike published a poem about them in The New Yorker:

The Earth is just a silly ball

To them through which they pass

Like dustmaids down a drafty hall

Or photons through a sheet of glass.

Neutrino time-travel jokes have proliferated on the Internet. Example: “We don’t serve faster-than-light neutrinos here,” said the bartender. A neutrino walks into a bar.

Under a YouTube video of the Corrigan Brothers (who played at President Obama’s inauguration), one commenter observed: “Irish Folk & particle physics — what a combo.”

The neutrino news came from a group of physicists based at the Gran Sasso underground laboratory in Italy and doing business under the apt acronym Opera. The neutrinos, they reported on Sept. 23 in a paper and at a special symposium at CERN, the European Center for Nuclear Research, had beaten a metaphorical light beam from CERN to Gran Sasso, a distance of 457 miles, by 60 nanoseconds.

The initial response of physicists assembled at CERN and around the world was that there was probably a mistake somewhere in the experiment. Einstein’s theory is the basis of all modern physics, and has been tested a zillion times.

Technically, relativity does allow some particles, known as tachyons, to go faster than light — in fact it forbids them to slow down to light speed. The hitch is that they would have imaginary masses, whatever that means. And there is also the possibility, in some versions of string theory, of particles’ taking a shortcut through another dimension. But allowing anything to travel faster than light would open up the possibility of all kinds of problems with cause and effect and even time travel.

“It looks too big to be true,” Alvaro de Rujala, a CERN theorist, said at the time.

Or as the Corrigan Brothers put it:

Was old Albert wrong?

Oh can it be,

that fabulous theory —

relativity —

is being debunked

for the first time?

But he still might be right,

old Albert Einstein.

Physicists, in the meantime, have been flooding arXiv.org, the physics Internet archive, with papers debunking the Opera experiment and defending Einstein. In one paper, two professors from Boston University, Andrew G. Cohen and the Nobelist Sheldon L. Glashow, showed that if the neutrinos had been going faster than light en route to Gran Sasso, they would have lost energy at a fearsome rate by emitting other particles, causing distortions in the beam that were not seen by Opera.

Another paper — by Gian Giudice of CERN, Sergei Sibiryakov of the Institute for Nuclear Research in Moscow and Alessandro Strumia of the University of Pisa in Italy and the National Institute of Chemical Physics and Biophysics in Tallinn, Estonia — argued that according to the Standard Model, the reigning theory in particle physics, if neutrinos could violate relativity, electrons should violate it also, something that has also not been observed.

Last week, in what sounded like the coup de grâce in some circles, Ronald A. J. van Elburg, an artificial intelligence researcher at the University of Groningen in the Netherlands, suggested that the Opera group had failed to make a relativistic correction for the motions of the GPS satellites used in timing the neutrino beams. The resulting error, he said, amounted to 64 nanoseconds, almost exactly the universe-shaking discrepancy the Opera researchers were hoping to explain.

That paper got wide attention. It was mentioned on a physics blog of the magazine Technology Review, and was published by the Massachusetts Institute of Technology and other news sites around the Internet as a possible explanation of the neutrino mystery. “If it stands up, this episode will be laden with irony,” Technology Review wrote. Far from breaking Einstein’s relativity, it went on, “the faster-than-light measurement will turn out to be another confirmation of it.”

The Opera collaborators and other outside physicists now say Dr. van Elburg’s analysis is wrong and reflects confusion about how GPS systems work.

In an e-mail, Antonio Ereditato, a spokesman for Opera, said the paper did have some errors, but he declined to go into details. “You understand well that we cannot reply to anybody claiming to have an explanation of our result in terms of trivial mistakes,” he said.

Reached in Groningen, Dr. van Elburg said that an improved version of his manuscript was now under peer review.

John Learned, a neutrino physicist at the University of Hawaii, wrote in an e-mail that while the Opera results might not be right, “they are still not easily dismissed.”

“It is very unlikely to me that any distant observer will point out the error of their ways,” he continued. “If a screw-up, it is probably in the details not accessible to outsiders.”

Meanwhile, Halloween is almost here. Don’t be surprised if you have already seen Einstein in a neutrino costume.

Sun's astrophysicist...John N. Bahcall

John N. Bahcall

1934-2005

"IAS's John N. Bahcall Probes the Lightweight Universe"

Science Watch

Ray Davis and John Bahcall

With his many contributions to neutrino astrophysics, John N. Bahcall has played a major part in opening a window on the universe. Thirty years ago Ray Davis, then working at Brookhaven National Laboratory and now at the University of Pennsylvania, suggested that it might be possible to detect neutrinos from the sun as a result of Bahcall's calculations on solar nuclear reactions. The unambiguous detection of these neutrinos directly verified the hypothesis that nuclear reactions generate stellar energy. A physicist with a deep interest in neutrino production in the universe, Bahcall graduated in physics from the University of California, Berkeley, in 1956. A master's from the University of Chicago followed a year later. For his doctorate, he was supervised by David Layzer of Harvard University, and after a postdoctoral position at Indiana University he moved to Caltech. Bahcall's interest in neutrinos was sparked early in his academic career. At Indiana he attended lectures given by Emil Kanapenski on weak interaction theory. As a self-imposed exercise for the student, he calculated some reaction rates. Later, an astronomer pointed him to the paper on cosmic nucleosynthesis by Margaret Burbidge, Geoffrey Burbidge, Willie Fowler, and Fred Hoyle (E.M. Burbidge, et al., Rev. Mod. Phys., 29:547, 1957). When Bahcall read the appendix, he saw that laboratory reaction rates had been used for beta decay in stellar interiors, but from his own calculations on beta decay he realized that the rates in stars would be very different from those in the laboratory. Since 1970 Bahcall has been an astrophysicist at the Institute for Advanced Study in Princeton, New Jersey. His interests range much more widely than studies of solar neutrinos, and include the search for dark matter in the universe and models of the galaxy. Most recently he has taken a leading role in applying the Hubble Space Telescope to studies of quasars. At a recent meeting of the American Astronomical Society, both Bahcall and Davis received prizes for their work on solar neutrinos, and Bahcall spoke to Science Watch's Physics correspondent Simon Mitton about his work in neutrino astrophysics.

SW: Your association with Willie Fowler, who died recently, was a long and fruitful one. How did that arise?

Bahcall: I wrote a short paper saying that the weak interaction rates being used by astrophysicists could not be correct because the laboratory rates would be changed in stars: ionization and the Pauli principle would play an effect at the high densities inside stars. Willie Fowler was the referee for that, and he was always very generous when there was a new idea. He invited me to the Kellogg Radiation Laboratory at Caltech to continue my work on weak interactions. At the same time Fowler wrote to Ray Davis saying I'd done some interesting calculations relevant to nuclear reactions in the sun. Ray expressed an interest in the rates for electron capture by 7Be, saying that he would love to build a detector for the neutrinos produced by the 7Be. Fowler encouraged me to work on this, and for the last 33 years Ray and I have been interacting more or less continuously.

SW: Throughout your period of collaboration with Ray Davis, the story of solar neutrino hunting has been one of the observed flux lagging the predicted rate, with the observed rates one-half or less than predicted. Your two most highly cited papers in Reviews of Modern Physics—on the solar models and neutrino rates—have recorded more than 700 citations between them, which is high for physical sciences papers. What have we learned about neutrino astronomy from the research sparked by these papers?

Bahcall: On a primitive level we've got a very fundamental result: we've confirmed experimentally that the sun shines by burning nuclear material in its core! This resolved a controversy that goes back to the middle of the 19th century. Advances in geology had shown the great age of Earth and raised the question for astronomers of how the sun could generate energy for millions of years. Eddington, in the early part of the 20th century, suggested that nuclear fusion is the source of that energy, but it took another 20 years before Hans Bethe developed fully the theory of nuclear reactions inside the sun. Ray confirmed this theory with his famous chlorine experiment conducted deep underground in Lead, South Dakota, in which a few atoms of 37Ar are produced each month when a 37Cl atom captures a solar neutrino. Today, three further experiments have detected neutrinos, and there is no doubt that they come from the sun. In the Kamiokande experiment (Japan), neutrino-electron scattering occurs. The Cerenkov light from scattered electrons shows that the high-energy 8B neutrinos causing the scattering have come from the direction of the sun. Two gallium experiments, GALLEX (Italy) and SAGE (Russia), detect the low-energy neutrinos from the basic proton-proton fusion reaction. These use absorption of a neutrino by 71Ga to produce 71Ge and an electron. The neutrino flux is measured to an accuracy of about 10%. So all four experiments detect solar neutrinos. The measured flux is the same as the predictions to within a factor of about 2-4 too little, depending on the experiment, and their energies are exactly what we expect from the theory. The data are specifically in agreement with the idea that the sun shines by burning four protons to form 4He, emitting two neutrinos in the cycle. This is in contrast with the reactions Hans Bethe thought were dominant, in which C, N, and O nuclei catalyze the four protons. So we've learned that reactions among the lightest nuclei alone keep dwarf stars like the sun shining. The interest shown in my 1982 and 1988 papers shows what a tremendous achievement it has been for a huge community of physicists, engineers, chemists, and astrophysicists—hundreds of people—to demonstrate what goes on deep inside stars. We've answered the question of how the stars shine and evolve.

SW:Your solar modeling work tries to reconcile theory and experiment, and in the course of this you have taken an interest in helioseismology, which aims to probe the solar interior by analyzing the oscillations of the sun's outer layers.

Bahcall: I've written a series of papers in which the goal is to calculate as precisely as possible the conditions in the solar interior. We successfully refined these models so we now get detailed agreement with the helioseismological frequencies, maybe 10,000 of which are known very accurately. So we now know what makes the sun tick much better than we did early on.

SW: All this progress cannot conceal the fact that astrophysicists still refer to the "solar neutrino problem."

Bahcall: Actually there are three solar neutrino problems. First, the classic one involving Ray's chlorine experiment, which has existed for two decades, in which there is a discrepancy between predicted and measured fluxes. Second, the water experiment at Kamiokande is apparently measuring the same thing as Ray—rare high-energy 8B solar neutrinos—but at different threshold energies, and they get different answers by nearly a factor of 2. The two experiments are ostensibly measuring the same process if the standard electroweak theory is correct. This "second" solar neutrino problem is independent of most of the uncertainties in astrophysics and nuclear physics. The third problem is that the gallium experiments are inconsistent with the robust predictions of the standard solar model for the flux of 7Be neutrinos. The dilemma is that either the chlorine or water experiment is wrong, and both of the gallium experiments are wrong, or we need new physics.

SW: This work is part of a long tradition in astrophysics whereby discoveries in the cosmos have informed physical theory. To what extent has the solar neutrino problem contributed to physics?

Bahcall: Neither Ray nor I had a vision that looking at a beam of neutrinos from an object 1011m away would teach us new physics. The two most popular mechanisms for explaining the solar neutrino problem via new physics are vacuum neutrino oscillations and matter-enhanced neutrino oscillations. Vladimir Gribov and Bruno Pontecorvo suggested that some sort of schizophrenia between the three neutrino types—electron, muon, and tau—on the long trip from the sun might mean that they switched to mainly muon or tau types by the time they got to Earth. That theory attracted a minority of particle physicists for a time. For the matter-enhanced oscillations we need a natural extension to the simplest version of standard electroweak theory. According to this explanation, some electron neutrinos are transformed into muon or tau neutrinos as a result of their interaction with electrons in the sun. Non-zero neutrino masses are required for this effect: theory and all experiments are reconciled with an electron neutrino mass of about 0.003 eV.

SW: Is the end in sight for the classical solar neutrino problem?

Bahcall: Four new solar neutrino experiments now under construction will soon test the proposition that new physics is needed. The Superkamiokande and the Sudbury Neutrino Observatory should be operational next year, and will have counting rates two orders of magnitude higher than the four pioneering experiments. Another experiment, being developed at CERN in Geneva, will look at the shape of the energy spectrum of 8B solar neutrinos, and this will tell us whether oscillations are taking place. My guess is that as a result of these experiments we will get directed in more specific ranges, but I don't think that it will be possible before the end of the century to say that there is a unique particle physics solution to solar neutrino problems. My hunch is that in the next five years or so it will be likely one of the several proposed particle physics solutions will emerge as the selected one. But there is sufficient richness in the imagination of our particle theorist friends that the number of particle physics solutions far exceeds the number of funded experiments! More than half of those scientists presently in the field incline to the matter-induced oscillations, but to focus on the solution with the rigor that is required will take more than the current generation of experiments but we might be lucky.

SW: A good example of astronomer's luck was the supernova explosion in the Large Magellanic Cloud in 1987, which led to the detection of neutrinos from beyond our galaxy. How do you see neutrino astronomy developing generally?

Bahcall: One active area with a lot of experiments is the study of atmospheric neutrinos, which has puzzles of its own. There is no doubt that at the very high energies at which cosmic rays come in they are producing neutrino secondaries. That too has interesting physics and will be active in the next decade. Beyond that there is true neutrino astronomy where we're looking for neutrinos in our galaxy and beyond. There are new experiments at the South Pole, under the ocean in Hawaii, and planned for under the sea near Greece, where people will be taking the first steps towards detecting on a regular basis neutrinos from other astronomical systems. We hope this will teach us about astronomical systems that are very different from those we see with photons: neutrinos come from very different regions to photons and they don't have the same difficulties in escaping from stars. I think these experiments are very promising. The first generation of these experiments will be operating in the next two to three years. Although they might not detect neutrinos from outside the solar system, the next generation will have much larger versions of the current experiments and I am hopeful we will then have extragalactic neutrino astronomy.

Princeton University obituary:

"Eminent astrophysicist John Bahcall dies at 70"

by

Eric Quiñones

August 18, 2005

John Bahcall, a renowned astrophysicist and faculty member of the Institute for Advanced Study who also was a visiting lecturer with rank of professor at Princeton, died Wednesday, Aug. 17, in New York City. He was 70. Bahcall, the Richard Black Professor of Astrophysics in the School of Natural Sciences at the Institute for Advanced Study, had a long and prolific career in astronomy and astrophysics. His work spanned five decades and included the publication of more than 500 technical papers, books and popular articles. His distinguished career included numerous honors and awards, including the National Medal of Science. In 1971, the same year Bahcall joined the institute as a permanent faculty member, he also accepted a continuing appointment as visiting lecturer at Princeton, where he served as an important link between the two institutions and fostered cooperation and coordination between their faculties. "John Bahcall worked closely and effectively with the University for over three decades to develop the community of Princeton astronomers and astrophysicists, both at the University and the institute, into one of the strongest and most vigorous in the world," said Scott Tremaine, chair of Princeton's Department of Astrophysical Sciences. "John strengthened our department at every level, from supervising undergraduate and graduate students in research projects to helping to identify and recruit senior faculty, and as a result I and my predecessors were in contact with him on an almost daily basis," Tremaine said. "John was also the astronomy community's most effective and prolific talent scout -- over half of the faculty members in our department were hired by him early in their careers, and I'm sure the same remarkable statistic is true of many of the best astronomy departments in the country." Bahcall is survived by his wife Neta Bahcall, a professor of astrophysics at Princeton; sons Safi and Dan; daughter Orli; and brother Robert.

Solo and co-authored papers:

arXiv

And...

An Iron Core For The Sun And More?