Peter Woit has blogged about an oral history interview with theoretical physicist Sheldon Glashow published in 2020 by the American Institute of Physics. (They have a great oral history of physics series you should check out if you’re interested.) Woit zeroed in on a portion in which Glashow talks about his faltering friendship with Steven Weinberg and his issues with Abdus Salam’s nomination for the physics Nobel Prize.
Glashow, Weinberg and Salam together won this prize in 1979, for their work on the work on electroweak theory, which describes the behaviour of two fundamental forces, the electromagnetic force and the weak force. Glashow recalls that his and Weinberg’s friendship – having studied and worked together for many years – deteriorated in the 1970s, a time in which both scientists were aware that they were due a Nobel Prize. According to Glashow, however, Weinberg wanted the prize to be awarded only to himself and Salam.
This is presumably because of how the prize-winning work came to be: with Glashow’s mathematical-physical model published in 1960, Weinberg building on it seven years later, with Salam’s two relevant papers appeared a couple years after Glashow’s paper and a year after Weinberg’s. Glashow recalls that Salam’s work was not original, that each of his two papers respectively echoed findings already published in Glashow’s and Weinberg’s papers. Instead, Glashow continues, Salam received the Nobel Prize probably because he had encouraged his peers and his colleagues to nominate him a very large number of times and because he set up the International Centre for Theoretical Physics (ICTP) in Trieste.
This impression, of Salam being undeserving from a contribution-to-physics point of view in Glashow’s telling, is very at odds with the impression of Salam based on reading letters and comments by Weinberg and Pervez Hoodbhoy and by watching the documentary Salam – The First ****** Nobel Laureate.
The topic of Salam being a Nobel laureate was never uncomplicated, to begin with: he was an Ahmadi Muslim who enjoyed the Pakistan government’s support until he didn’t, when he was forced to flee the country; his intentions with the ICTP – to give scholars from developing countries a way to study physics without having to contend with often-crippling resource constrains – were also noble. Hoodbhoy has also written about the significance of Salam’s work as a physicist and the tragedy of his name and the memories of his contributions having been erased from all the prominent research centres in Pakistan.
Finally, one of Salam’s nominees for a Nobel Prize was the notable British physicist and Nobel laureate Paul A.M. Dirac, and it seems strange that Dirac would endorse Salam if he didn’t believe Salam’s work deserved it.
Bearing these facts in mind, Glashow’s contention appears to be limited to the originality of Salam’s work. But to my mind, even if Salam’s work was really derivative, it was at par with that of Glashow and Weinberg. More importantly, while I believe the Nobel Prizes deserve to be abrogated, the prize-giving committee did more good than it might have realised by including Salam among its winners: in the words of Weinberg, “Salam sacrificed a lot of possible scientific productivity by taking on that responsibility [to set up ICTP]. It’s a sacrifice I would not make.”
Glashow may not feel very well about Salam’s inclusion for the 1979 prize and the Nobel Prizes as we know are only happy to overlook anything other than the scientific work itself, but if the committee really screwed up, then they screwed up to do a good thing.
Then again, even though Glashow wasn’t alone (he was joined by Martinus J.G. Veltman on his opinions against Salam), the physicists’ community at large doesn’t share his views. Glashow also cites an infamous 2014 paper by Norman Dombey, in which Dombey concluded that Salam didn’t deserve his share of the prize, but the paper’s reputation itself is iffy at best.
In fact, this is all ultimately a pointless debate: there are just too many people who deserve a Nobel Prize but don’t win it while a deeper dive into the modern history of physics should reveal a near-constant stream of complaints against Nobel laureates and their work by their peers. It should be clear today that both winning a prize and not winning a prize ought to mean nothing to the practice of science.
The other remarkable thing about Glashow’s comments in the interview (as cited by Woit) is what I like to think of as the seemingly eternal relevance of Brian Keating’s change of mind. Brian Keating is an astrophysicist who was at the forefront of the infamous announcement that his team had discovered evidence of cosmic inflation, an epoch of the early universe in which it is believed to have expanded suddenly and greatly, in March 2014. There were many problems leading up to the announcement but there was little doubt at the time, and Keating also admitted later, that its rapidity was motivated by the temptation to secure a Nobel Prize.
Many journalists, scientists and others observers of the practice of science routinely and significantly underestimate the effect the Nobel Prizes exert on scientific research. The prospect of winning the prize for supposedly discovering evidence of cosmic inflation caused Keating et al. to not wait for additional, confirmatory data before making their announcement. When such data did arrive, from the Planck telescope collaboration, Keating et al. suffered for it with their reputation and prospects.
Similarly, Weinberg and Glashow fell out because, according to Glashow, Weinberg didn’t wish Glashow to give a talk in 1979 discussing possible alternatives to the work of Weinberg and Salam because Weinberg thought doing such a thing would undermine his and Salam’s chances of being awarded a Nobel Prize. Eventually it didn’t, but that’s beside the point: this little episode in history is as good an illustration as any of how the Nobel Prizes and their implied promises of laurels and prestige render otherwise smart scientists insecure, petty and elbows-out competitive – in exchange for sustaining an absurd and unjust picture of the scientific enterprise.
All of this goes obviously against the spirit of science.
Featured image: From left to right: Tom Kibble, Gerald Guralnik, Richard Hagen, François Englert and Robert Brout. Credit: Wikimedia Commons.
Sir Tom Kibble passed away on June 2, I learnt this morning with a bit of sadness that I’d missed the news. It’s hard to write about someone in a way that prompts others either to find out more about that person or, if they knew him or his work, to recall their memories of him when I myself would like only to do the former now. So let me quickly spell out why I think you should pay attention: Kibble was one of the six theorists who, in 1964, came up with the ABEGHHK’tH mechanism to explain how gauge bosons acquired mass. The ‘K’ in those letters stands for ‘Kibble’. However, we only remember that mechanism with the second ‘H’, which stands for Higgs; the other letters fell off for reasons not entirely clear – although convenience might’ve played a role. And while everyone refers to the mechanism as the Higgs mechanism, Peter Higgs, the man himself, continues to call it the ABEGHHK’tH mechanism.
Anyway, Kibble was known for three achievements. The first was to co-formulate – alongside Gerald Guralnik and Richard Hagen – the ABEGHHK’tH mechanism. It was validated in early 2013, earning only Higgs and ‘E’, François Englert, the Nobel Prize for physics that year. The second came in 1967, to explain how the mechanism accords the W and Z bosons, the carriers of the weak nuclear force, with mass but not the photons. The solution was crucial to validate the electroweak theory, and whose three conceivers (Sheldon Glashow, Abdus Salam and Steven Weinberg) won the Nobel Prize for physics in 1979. The third was the postulation of the Kibble-Żurek mechanism, which explains the formation of topological defects in the early universe by applying the principles of quantum mechanics to cosmological objects. This work was done alongside the Polish-American physicist Wojciech Żurek.
I spoke to Kibble once, only for a few minutes, at a conference at the Institute of Mathematical Sciences, Chennai, in December 2013 (at the same conference where I met George Sterman as well). This was five months after Fabiola Gianotti had made the famous announcement at CERN that the LHC had found a particle that looked like the Higgs boson. I’d asked Kibble what he made of the announcement, and where we’d go from here. He said, as I’m sure he would’ve a thousand times before, that it was very exciting to be proven right after 50 years; that it’d definitively closed one of the biggest knowledge gaps in modern theoretical particle physics; and that there was still work to be done by studying the Higgs boson for more clues about the nature of the universe. He had to rush; a TV crew was standing next to me, nudging me for some time with him. I was glad to see it was Puthiya Thalaimurai, a Tamil-language news channel, because it meant the ‘K’ had endured.
Looking into a section of the 6.3-km long HERA tunnel at Deutsches Elektronen-Synchrotron (DESY), Hamburg. Source: DESY
For many years, one of the world’s most powerful scopes, as in a microscope, was the Hadron-Elektron Ring Anlage (HERA) particle accelerator in Germany. Where scopes bounce electromagnetic radiation – like visible light – off surfaces to reveal information hidden to the naked eye, accelerators reveal hidden information by bombarding the target with energetic particles. At HERA, those particles were electrons accelerated to 27.5 GeV. At this energy, the particles can probe a distance of a few hundredths of a femtometer (earlier called fermi) – 2.5 million times better than the 0.1 nanometers that atomic force microscopy can achieve (of course, they’re used for different purposes).
The electrons were then collided head on against protons accelerated to 920 GeV.
Unlike protons, electrons aren’t made up of smaller particles and are considered elementary. Moreover, protons are approx. 2,000-times heavier than electrons. As a result, the high-energy collision is more an electron scattering off of a proton, but the way it happens is that the electron imparts some energy to the proton before scattering off (this is imagined as an electron emitting some energy as a photon, which is then absorbed by the proton). This is called deep inelastic scattering: ‘deep’ for high-energy; ‘inelastic’ because the proton absorbs some energy.
One of the most famous deep-inelastic scattering experiments was conducted in 1968 at the Stanford Linear Accelerator Centre. Then, the perturbed protons were observed to ’emit’ other particles – essentially hitherto undetected constituent particles that escaped their proton formation and formed other kinds of composite particles. The constituent particles were initially dubbed partons but later found to be quarks, anti-quarks (the matter/anti-matter particles) and gluons (the force-particles that held the quarks/anti-quarks together).
HERA was shut in June 2007. Five years later, the plans for a successor at least 100-times more sensitive than HERA were presented – in the form of the Large Hadron-electron Collider (LHeC). As the name indicates, it is proposed to be built adjoining the Large Hadron Collider (LHC) complex at CERN by 2025 – a timeframe based on when the high-luminosity phase of the LHC is set to begin (2024).
Timeline for the LHeC. Source: CERN
On December 15, physicists working on the LHC had announced new results obtained from the collider – two in particular stood out. One was a cause for great, yet possibly premature, excitement: a hint of a yet unknown particle weighing around 747 GeV. The other was cause for a bit of dismay: quantum chromodynamics (QCD), the theory that deals with the physics of quarks, anti-quarks and gluons, seemed flawless across a swath of energies. Some physicists were hoping it wouldn’t be so (because its flawlessness has come at the cost of being unable to explain some discoveries, like dark matter). Over the next decade, the LHC will push the energy frontier further to see – among other things – if QCD ‘breaks’, becoming unable to explain a possible new phenomenon.
Against this background, the LHeC is being pitched as the machine that could be dedicated to examining this breakpoint and some other others like it, and in more detail than the LHC is equipped to. One helpful factor is that when electrons are one kind of particles participating in a collision, physicists don’t have to worry about how the energy will be distributed among constituent particles since electrons don’t have any. Hadron collisions, on the other hand, have to deal with quarks, anti-quarks and gluons, and are tougher to analyse.
An energy recovery linac (in red) shown straddling the LHC ring. A rejected design involved installing the electron-accelerator (in yellow) concentrically with the LHC ring. Source: CERN
So, to accomplish this, the team behind the LHeC is considering installing a pill-shaped machine called the energy recovery linac (ERL), straddling the LHC ring (shown above), to produce a beam of electrons that’d then take on the accelerated protons from the main LHC ring – making up the ‘linac-ring LHeC’ design. A first suggestion to install the LHeC as a ring, to accelerate electrons, along the LHC ring was rejected because it would hamper experiments during construction. Anyway, the electrons will be accelerated to 60 GeV while the protons, to 7,000 GeV. The total wall-plug power to the ERL is being capped at 100 MW.
The ERL has a slightly different acceleration mechanism from the LHC, and doesn’t simply accelerate particles continuously around a ring. First, the electrons are accelerated through a radio-frequency field in a linear accelerator (linac – the straight section of the ERL) and then fed into a circular channel, crisscrossed by magnetic fields, curving into the rear end of the linac. The length of the circular channel is such that by the time the electrons travel along it, their phase has shifted by 180º (i.e. if their spin was oriented “up” at one end, it’d have become flipped to “down” by the time they reached the other). And when the out-of-phase electrons reenter the channel, they decelerate. Their kinetic energy is lost to the RF field, which intensifies and so provides a bigger kick to the new batch of particles being injected to the linac at just that moment. This way, the linacrecovers the kinetic energy from each circulation.
Such a mechanism is employed at all because the amount of energy lost in a form called synchrotron radiation increases drastically as the particle’s mass gets lower – when accelerated radially using bending magnetic fields.
The bluish glow from the central region of the Crab Nebula is due to synchrotron radiation. Credit: NASA-ESA/Wikimedia Commons
Keeping in mind the need to explore new areas of physics – especially those associated with leptons (elementary particles of which electrons are a kind) and quarks/gluons (described by QCD) – the energy of the electrons coming out of the ERL is currently planned to be 60 GeV. They will be collided with accelerated protons by positioning the ERL tangential to the LHC ring. And at the moment of the collision, CERN’s scientists hope that they will be able to use the LHeC to study:
Predicted unification of the electromagnetic and weak forces (into an electroweak force): The electromagnetic force of nature is mediated by the particles called photons while the weak force, by particles called W and Z bosons. Whether the scientists will observe the unification of these forces, as some theories predict, is dependent on the quality of electron-proton collisions. Specifically, if the square of the momentum transferred between the particles can reach up to 8-9 TeV, the collider will have created an environment in which physicists will be able to probe for signs of an electroweak force at play.
Gluon saturation: To quote from an interview given by theoretical physicist Raju Venugopalan in January 2013: “We all know the nuclei are made of protons and neutrons, and those are each made of quarks and gluons. There were hints in data from the HERA collider in Germany and other experiments that the number of gluons increases dramatically as you accelerate particles to high energy. Nuclear physics theorists predicted that the ions accelerated to near the speed of light at the [Relativistic Heavy Ion Collider] would reach an upper limit of gluon concentration – a state of gluon saturation we call colour glass condensate.”
Higgs bosons: On July 4, 2012, Fabiola Gianotti, soon to be the next DG of CERN but then the spokesperson of the ATLAS experiment at the LHC, declared that physicists had found a Higgs boson. Widespread celebrations followed – while a technical nitpick remained: physicists only knew the particle resembled a Higgs boson and might not have been the real thing itself. Then, in March 2013, the particle was most likely identified as being a Higgs boson. And even then, one box remained to be checked: that it was the Higgs boson, not one of many kinds. For that, physicists have been waiting for more results from the upgraded LHC. But a machine like the LHeC would be able to produce a “few thousand” Higgs bosons a year, enabling physicists to study the elusive particle in more detail, confirm more of its properties – or, more excitingly, find that that’s not the case – and look for higher-energy versions of it.
A 2012 paper detailing the concept also notes that should the LHC find that signs of ‘new physics’ could exist beyond the default energy levels of the LHeC, scientists are bearing in mind the need for the electrons to be accelerated by the ERL to up to 140 GeV.
The default configuration of the proposed ERL. The bending arcs are totally about 19 km long (three to a side at different energies). Source: CERN
The default configuration of the proposed ERL. The bending arcs are totally about 19 km long (three to a side at different energies). Source: CERN
The unique opportunity presented by an electron-proton collider working in tandem with the LHC goes beyond the mammoth energies to a property called luminosity as well. It’s measured in inverse femtobarn per second, denoting the number of events occurring per 10-39 squared centimetres per second. For example, 10 fb-1 denotes 10 events occurring per 10-39 sq. cm s-1 – that’s 1040 events per sq. cm per second (The luminosity over a specific period of time, i.e. without the ‘per seconds’ in the unit, is called the integrated luminosity). At the LHeC, a luminosity of 1033 cm-2 s-1 is expected to be achieved and physicists hope that with some tweaks, it can be hiked by yet another order of magnitude. To compare: this is 100x what HERA achieved, providing an unprecedented scale at which to explore the effects of deep inelastic scattering, and 10x the LHC’s current luminosity.
It’s also 100x lower than that of the HL-LHC, which is the configuration of the LHC with which the ERL will be operating to make up the LHeC. And the LHeC’s lifetime will be the planned lifetime of the LHC, till the 2030s, about a decade. In the same period, if all goes well, a Chinese behemoth will have taken shape: the Circular Electron-Positron Collider (CEPC), with a circumference 2x that of the LHC. In its proton-proton collision configuration – paralleling the LHC’s – China claims it will reach energies of 70,000 GeV (as against the LHC’s current 14,000 GeV) and luminosity comparable to the HL-LHC. And when its electron-positron collision configuration, which the LHeC will be able to mimic, will be at its best, physicists reckon the CEPC will be able to produce 100,000 Higgs bosons a year.
Timeline for operation of the Future Circular Collider being considered. Source: CERN
As it happens, some groups at CERN are already drawing up plans, due to be presented in 2018, for a machine dwarfing even the CEPC. Meet the Future Circular Collider (FCC), by one account the “ultimate precision-physics machine” (and funnily named by another). To be fair, the FCC has been under consideration since about 2013 and independent of the CEPC. However, in sheer size, the FCC could swallow the CEPC – with an 80-100 km-long ring. It will also be able to accelerate protons to 50,000 GeV (by 2040), attain luminosities of 1035 cm-2 s-1, continue to work with the ERL, function as an electron-positron collider (video), and look for particles weighing up to 25,000 GeV (currently the heaviest known fundamental particle is the top quark, weighing 169-173 GeV).
An illustration showing a possible location and size, relative to the LHC (in white) of the FCC. The main tunnel is shown as a yellow dotted line. Source: CERN
And should it be approved and come online in the second half of the 2030s, there’s a good chance the world will be a different place, too: not just the CEPC – there will be (or will have been?) either the International Linear Collider (ILC) and Compact Linear Collider (CLIC) as well. ‘Either’ because they’re both linear accelerators with similar physical dimensions and planning to collide electrons with positrons, their antiparticles, to study QCD, the Higgs field and the prospects of higher dimensions, so only one of them might get built. And they will require a decade to be built, coming online in the late 2020s. The biggest difference between them is that the ILC will be able to reach collision energies of 1,000 GeV while the CLIC (whose idea was conceived at CERN), of 3,000 GeV.
FCC-he = proton-electron collision mode; FCC-hh = proton-proton collision mode; SppC = CEPC’s proton-proton collision mode.