Tag: Large Hadron Collider

• Worlds between theory and experiment

  Once Isaac Newton showed that a single gravitational law plus his rules of dynamics could reproduce the orbits of planets that Johannes Kepler had predicted, explain tides on Earth, and predict that a comet that had passed by once would return again, physicists considered Newtonian mechanics and gravitation to have been completely validated. After these successful tests, they didn’t wait to test every other possible prediction of Newton’s ideas before they considered them to be legitimate.

  When Jean Perrin and others carefully measured Brownian motion and extracted Avogadro’s number in the early 20th century, they helped cement the science of the kinetic theory of gases and statistical mechanics that Ludwig Boltzmann and Josiah Willard Gibbs had developed. As with Newtonian mechanics, physicists didn’t also require every single consequence of kinetic theory to be rechecked from scratch. They considered them all to be fully and equally legitimate then on.

  Similarly, in 1886-1889, Heinrich Hertz produced and detected electromagnetic waves in the laboratory, measured their speed and other physical properties, and showed that they behaved exactly as James Clerk Maxwell had predicted based on his (famous) equation. Hertz’s experiments didn’t test every possible configuration of charges and fields that Maxwell’s equations allowed, yet what they did test and confirm sufficed to convince all physicists that Maxwell’s theory could be treated as the correct classical theory of electromagnetism.

  In all these cases, a theory won broad acceptance after scientists validated only a small (yet robust) subset of its predictions. They didn’t have to validate every single prediction in distinct experiments.

  However, there are many ideas in high-energy particle physics that, even as they are derived from other theoretical constructs that have been tested to extreme precision, physicists insist on testing them anew as well. Why are they going to this trouble now?

  “High-energy particle physics” is a four-word label for something you’ve likely already heard of: the physics of the search for the subatomic particles like the Higgs boson and the efforts to identify their properties.

  In this enterprise, many scientific ideas follow from theories that have been validated by very large amounts of experimental data. Yet physicists want to test them at every single step because of the way such theories are built and the way unknown effects can hide inside their structures.

  The overarching theory that governs particle physicists is called, simply, the Standard Model. It’s a quantum field theory, i.e. a theory that combines the precepts of quantum mechanics and special relativity*. Because the Standard Model is set up in this way, it makes predictions about the relations between different observable quantities, e.g. the mass of a subatomic particle called the W boson with a parameter that’s related to the decay of other particles called muons. Some of these relations connect measured quantities with others that have not yet been probed, e.g. the mass of the muon with the rate at which Higgs bosons decay to pairs of muons. (Yes, it’s all convoluted.) These ‘extra’ relations often depend on assumptions that go beyond the domains that experiments have already explored. New particles and new interactions between them can change particular parts of the structure while leaving other parts nearly unchanged.

  (* Quantum field theory gives physicists a single, internally consistent framework in which they can impose both the rules of quantum theory and the requirements of special relativity, such as that information or matter can’t travel faster than light and that our spacetime conserves energy and momentum together, for example. However, quantum field theory does not unify quantum theory with general relativity; that’s the monumental and still unfinished purpose of the quantum gravity problem.)

  For a more intricate example, consider the gauge sector of the Standard Model, i.e. the parts of the Model involving the gluons, W and Z bosons, and photons, their properties, and their interactions with other particles. The gauge sector has been thoroughly tested in experiments and is well-understood. Now, the gauge sector also interacts with the Higgs sector, and the Higgs sector interacts with other sectors. The result is new possibilities involving the properties of the Higgs boson, their implications for the gauge sector, and so on that — even if physicists have tested the gauge sector — need to be tested separately. The reason is that none of these possibilities follow directly from the basic principles of the gauge sector.

  The search for ‘new physics’ also drives this attitude. ‘New physics’ refers to measurable entities and physical phenomena that lie beyond what the Standard Model can currently describe. For instance, most physicists believe a substance called dark matter exists (in order to explain some anomalous observations about the universe), but they haven’t been able to confirm what kind of particles dark matter is made of. One popular proposal is that dark matter is made of hitherto unknown entities called weakly interacting massive particles (WIMPs). The Standard Model in its contemporary form doesn’t have room for WIMPs, so the search for WIMPs is a search for new physics.

  Physicists have also proposed many ways to ‘extend’ the Standard Model to accommodate new kinds of particles that ‘repair’ the cracks in reality left by the existing crop of particles. Some of these extensions predict changes to the Model that are most pronounced in sectors that are currently poorly pinned down by existing data. This means even a sizeable deviation from the Model’s structure in this sector would still be compatible with all current measurements. This is another important reason physicists want to collect more data and with ever-greater precision.

  Earlier experience also plays an important role. Physicists may make some assumptions because they seem safe in some year but new data collected in the next two decades might reveal that they were mistaken. For instance, physicists believed neutrinos didn’t have mass, like photons, because that idea was consistent with many existing datasets. Yet dedicated experiments contradicted their belief (and won their performers the 2015 physics Nobel Prize).

  (Aside: High-energy particle physics uses large machines called particle colliders to coerce subatomic particles into configurations where they interact with each other, then collect data of those interactions. Operating these instruments demands hundreds of people working together, using sophisticated technologies and substantial computing resources. Because the instruments are so expensive, these collaborations aim to collect as much data as possible, then maximise the amount of information they extract from each dataset.)

  Thus, when a theory like the Standard Model predicts a specific process, that process becomes a thing to test. But even if the prediction seems simple or obvious, actually measuring it can still rule out whole families of rival theories offering to explain the same process. It also sharpens physicists’ estimates of the theory’s basic parameters, which then makes other predictions more precise and helps plan the next round of experiments. This is why, in high-energy physics, even predictions that follow from other, well-tested parts of a theory are expected to face experimental tests of their own. Each successful test can reduce the space for new physics to hide in — or in fact could reveal it.

  A study published in Physical Review Letters on December 3 showcases a new and apt example of testing predictions made by a theory some of whose other parts have already survived testing. Tests at the Large Hadron Collider (LHC) — the world’s largest, most powerful particle collider — had until recently only weakly constrained the Higgs boson’s interaction with second-generation leptons (a particle type that includes muons). The new study provides strong, direct evidence for this coupling and significantly narrows that gap.

  The LHC operates by accelerating two beams of protons in opposite directions to nearly the speed of light and smashing them head on. Its operation is divided into segments called ‘runs’. Between runs, the collaboration that manages the machine conducts maintenance and repair work and, sometimes, upgrades its detectors.

  One of the LHC’s most prominent detectors is named ATLAS. To probe the interactions between Higgs bosons and leptons, the ATLAS collaboration collected and analysed data from the LHC’s run 2 and run 3. The motivation was to obtain direct evidence for Higgs bosons’ coupling to muons and to measure its strength. And in the December 3 paper, the collaboration reported that the coupling parameters were consistent with the Standard Model’s predictions.

  So that’s one more patch of the Standard Model that has passed a test, and one more door to ‘new physics’ that has closed a little more.

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  Featured image: A view of the Large Hadron Collider inside its tunnel. Credit: CERN.

  2025.12.06

• Is the Higgs boson doing its job?

  At the heart of particle physics lies the Standard Model, a theory that has stood for nearly half a century as the best description of the subatomic realm. It tells us what particles exist, how they interact, and why the universe is stable at the smallest scales. The Standard Model has correctly predicted the outcomes of several experiments testing the limits of particle physics. Even then, however, physicists know that it’s incomplete: it can’t explain dark matter, why matter dominates over antimatter, and why the force of gravity is so weak compared to the other forces. To settle these mysteries, physicists have been conducting very detailed tests of the Model, each of which has either tightened their confidence in a hypothetical explanation or has revealed a new piece of the puzzle.

  A central character in this story is a subatomic particle called the W boson — the carrier of the weak nuclear force. Without it, the Sun wouldn’t shine because particle interactions involving the weak force are necessary for nuclear fusion to proceed. W bosons are also unusual among force carriers: unlike photons (the particles of light), they’re massive, about 80-times heavier than a proton. This mass difference — of a massless photon and a massive W boson — arises due to a process called the Higgs mechanism. Physicists first proposed this mechanism in 1964 and confirmed it was real when they found the Higgs boson particle at the Large Hadron Collider (LHC) in 2012.

  

  But finding the Higgs particle was only the beginning. To prove that the Higgs mechanism really works the way the theory says, physicists need to check its predictions in detail. One of the sharpest tests involves how W bosons scatter off each other at high energies. The key to achieving this is the W boson’s polarisation states. Both photons and W bosons have a property called quantum spin, but whereas for photons its value is zero, for W bosons its non-zero. The spin also has a direction. If it points sideways, the W boson is said to be transverse polarised; if it’s pointing along the particle’s direction of travel, the W boson is said to be longitudinally polarised. The longitudinal ones are special because their behaviour is directly tied to the Higgs mechanism.

  Specifically, if the Higgs mechanism and the Higgs boson don’t exist, calculations involving the longitudinal W bosons scattering off of each other quickly give rise to nonsensical mathematical results in the theory. The Higgs boson acts like a regulator in this engine, preventing the mathematics from ‘blowing up’. In fact, in the 1970s, the theoretical physicists Benjamin Lee, Chris Quigg, and Hugh Thacker showed that without the Higgs boson, the weak force would become uncontrollably powerful at high energies, leading to the breakdown of the theory. Their work was an important theoretical pillar that justified building the colossal LHC machine to search for the Higgs boson particle.

  https://withspeak.wpcomstaging.com/2025/06/24/technical-foundation-for-a-muon-collider-laid-at-j-parc/

  The terms Higgs boson, Higgs field, and Higgs mechanism describe related but distinct ideas. The Higgs field is a kind of invisible medium thought to fill all of space. Particles like W bosons and Z bosons interact with this field as they move and through that interaction they acquire mass. This is the Higgs mechanism: the process by which particles that would otherwise be massless become heavy.

  The Higgs boson is different: it’s a particle that represents a vibration or a ripple in the Higgs field, just as a photon is a ripple in the electromagnetic field. Its discovery in 2012 confirmed that the field is real and not just something that appears in the mathematics of the theory. But discovery alone doesn’t prove the mechanism is doing everything the theory demands. To test that, physicists need to look at situations where the Higgs boson’s balancing role is crucial.

  The scattering of longitudinally polarised W bosons is a good example. Without the Higgs boson, the probabilities of the scatterings occurring uncontrollably at higher energy, but with the Higgs boson in the picture, they stay within sensible bounds. Observing longitudinally polarised W bosons behaving as predicted is thus evidence for the particle as well as a check on the field and the mechanism behind it.

  Imagine a roller-coaster without brakes. As it goes faster and faster, there’s nothing to stop it from flying off the tracks. The Higgs mechanism is like the braking system that keeps the ride safe. Observing longitudinally polarised W bosons in the right proportions is equivalent to checking that the brakes actually work when the roller-coaster speeds up.

  

  Another path that physicists once considered and that didn’t involve a Higgs boson at all was called technicolor theory. Instead of a single kind of Higgs boson giving the W bosons their mass, technicolor proposed a brand-new force. Just as the strong nuclear force binds quarks into protons and neutrons, the hypothetical technicolor force would bind new “technifermion” particles into composite states. These bound states would mimic the Higgs boson’s job of giving particles mass, while producing their own new signals in high-energy collisions.

  The crucial test to check whether some given signals are due to the Higgs boson or due to technicolor lies in the behaviour of longitudinally polarised W bosons. In the Standard Model, their scattering is kept under control by the Higgs boson’s balancing act. In technicolor, by contrast, there is no Higgs boson to cancel the runaway growth. The probability of the scattering of longitudinally polarised W bosons would therefore rise sharply with more energy, often leaving clearly excessive signals in the data.

  Thus, observing longitudinally polarised W bosons at consistent with the predictions of the Standard Model, and not finding any additional signals, would also strengthen the case for the Higgs mechanism and weaken that for technicolor and other “Higgs-less” theories.

  At the Large Hadron Collider, the cleanest way to study look for such W bosons is in a phenomenon called vector boson scattering (VBS). In VBS, two protons collide and the quarks inside them emit W bosons. These W bosons then scatter off each other before decaying into lighter particles. The leftover quarks form narrow sprays of particles, or ‘jets’, that fly far forward.

  If the two W bosons happen to have the same electric charge — i.e. both positive or both negative — the process is even more distinctive. This same-sign WW scattering is quite rare and that’s an advantage because then it’s easy to spot in the debris of particle collisions.

  Both ATLAS and CMS, the two giant detectors at the LHC, had previously observed same-sign WW scattering without breaking down the polarisation. In 2021, the CMS detector reported the first hint of longitudinal polarisation but at a statistical significance only of 2.3 sigma, which isn’t good enough (particle physicists prefer at least 3 sigma). So after the LHC completed its second run in 2018, collecting data from around 10 quadrillion collisions between protons, the ATLAS collaboration set out to analyse it and deliver the evidence. This group’s study was published in Physical Review Letters on September 10.

  

  The challenge of finding longitudinally polarised W bosons is like finding a particular needle in a very large haystack where most of the needles look nearly identical. So ATLAS designed a special strategy.

  When one W boson decays, the result is one electron or muon and one neutrino. If the W boson is positively charged, for example, the decay could be to one anti-electron and one electron-neutrino or to one anti-muon and a muon-neutrino. Anti-electrons and anti-muons are positively charged. If the W boson is negatively charged, the products could one electron and one electron-antineutrino or one muon and one muon-antineutrino. So first, ATLAS zeroed in on the fact that it was looking for two electrons, two muons, or one of each, both carrying the same electric charge. Neutrinos however are really hard to catch and study, so the ATLAS group look for their absence rather than their presence. In all these particle interactions, the law of conservation of momentum holds — which means in a given interaction, a neutrino’s presence can be elucidated when the momenta of the electrons or muons add up to be slightly lower than that of the W boson; the missing amount would have been carried away by the neutrino, like money unaccounted for in a ledger.

  This analysis also required an event of interest to have at least two jets (reconstructed from streams of particles) with a combined energy above 500 GeV and separated widely in rapidity (which is a measure of their angle relative to the beam). This particular VBS pattern — two electrons/muons, two jets, and missing momentum — is the hallmark of same-sign WW scattering.

  Second, even with these strict requirements, impostors creep in. The biggest source of confusion is WZ production, a process in which another subatomic particle called the Z boson decays invisibly or one of its decay products goes unnoticed, making the event resemble WW scattering. Other sources include electrons having their charges mismeasured, jets can masquerading as electrons/muons, and some quarks producing electrons/muons that slip into the sample. To control for all this noise, the ATLAS group focused on control regions: subsets of events that produced a distinct kind of noise that the group could cleanly ‘subtract’ from the data to reveal same-sign WW scattering, thus also reducing uncertainty in the final results.

  Third, and this is where things get nuanced: the differences between transverse and longitudinally polarised W bosons show up in distributions — i.e. how far apart the electrons/muons are in angle, how the jets are oriented, and the energy of the system. But since no single variable could tell the whole story, the ATLAS group combined them using deep neural networks. These machine-learning models were fed up to 20 kinematic variables — including jet separations, particle angles, and missing momentum patterns — and trained to distinguish between three groups:

  (i) Two transverse polarised W bosons;

  (ii) One transverse polarised W boson and one longitudinally polarised W boson; and

  (iii) Both longitudinally polarised W bosons

  Fourth, the group combined the outputs of these neural networks and fit with a maximum likelihood method. When physicists make measurements, they often don’t directly see what they’re measuring. Instead, they see data points that could have come from different possible scenarios. A likelihood is a number that tells them how probable the data is in a given scenario. If a model says “events should look like this,” they can ask: “Given my actual data, how likely is that?” And the maximum likelihood method will help them decide the parameters that make the given data most likely to occur.

  For example, say you toss a coin 100 times and get 62 heads. You wonder: is the coin fair or biased? If it’s fair, the chance of exactly 62 heads is small. If the coin is slightly biased (heads with probability 0.62), the chance of 62 heads is higher. The maximum likelihood estimate is to pick the bias, or probability of heads, that makes your actual result most probable. So here the method would say, “The coin’s bias is 0.62” — because this choice maximises the likelihood of seeing 62 heads out of 100.

  In their analysis, the ATLAS group used the maximum likelihood method to check with the LHC data ‘preferred’ a contribution from longitudinal scattering, after subtracting what background noise and transverse-only scattering could explain.

  The results are a milestone in experimental particle physics. In the September 10 paper, ATLAS reported evidence for longitudinally polarised W bosons in same-sign WW scattering with a significance of 3.3 sigma — sufficiently close to 4, which is the calculated significance based on the predictions of the Standard Model. This means the data behaved as theory predicted, with no unexpected excess or deficit.

  It’s also bad news for technicolor theory. By observing longitudinal W bosons at exactly the rates predicted by the Standard Model, and not finding any additional signals, the ATLAS data strengthens the case for the Higgs mechanism providing the check on the W bosons’ scattering probability, rather than the technicolor force.

  The measured cross-section for events with at least one longitudinally polarised W boson was 0.88femtobarns, with an uncertainty of 0.3 femtobarns. These figures essentially mean that there were only a few hundred same-sign WW scattering events in the full dataset of around 10 quadrillion proton-proton collisions. The fact that ATLAS could pull this signal out of such a background-heavy environment is a testament to the power of modern machine learning working with advanced statistical methods.

  The group was also able to quantify the composition of signals. Among others:

  1. About 58% of events were genuine WW scattering
  2. Roughly 16% were from WZ production
  3. Around 18% arose from irrelevant electrons/muons, charge misidentification or the decay of energetic photons

  One way to appreciate the importance of these findings is by analogy: imagine trying to hear a faint melody being played by a single violin in the middle of a roaring orchestra. The violin is the longitudinal signal; the orchestra is the flood of background noise. The neural networks are like sophisticated microphones and filters, tuned to pick out the violin’s specific tone. The fact that ATLAS couldn’t only hear it but also measured its volume to match the score written by the Standard Model is remarkable.

  Perhaps in the same vein, these results are more than just another tick mark for the Standard Model. It’s a direct test of the Higgs mechanism in action. The discovery of the Higgs boson particle in 2012 was groundbreaking but proving that the Higgs mechanism performs its theoretical role requires demonstrating that it regulates the scattering of W bosons. By finding evidence for longitudinally polarised W bosons at the expected rate, ATLAS has done just that.

  The results also set the stage for the future. The LHC is currently being upgraded to a form called the High-Luminosity LHC and it will begin operating later this decade, collect datasets about 10x larger than what the LHC did in its second run. With that much more data, physicists will be able to study differential distributions, i.e. how the rate of longitudinal scattering varies with energy, angle or jet separation. These patterns are sensitive to hitherto unknown particles and forces, such as additional Higgs-like particles or modifications to the Higgs mechanism itself. That is, even small deviations from the Standard Model’s predictions could hint at new frontiers in particle physics.

  Indeed, history has often reminded physicists that such precision studies often uncover surprises. Physicists didn’t discover neutrino oscillations by finding a new particle but by noticing that the number of neutrinos arriving from the Sun at detectors on Earth didn’t match expectations. Similarly, minuscule mismatches between theory and observations in the scattering of W bosons could someday reveal new physics — and if they do, the seeds will have been planted by studies like that of the ATLAS group.

  https://withspeak.wpcomstaging.com/2025/09/06/challenging-the-neutrino-signal-anomaly/

  On the methodological front, the analysis also showcases how particle physics is evolving. ‘Classical’ analyses once banked on tracking single variables; now, deep learning has played a starring role by combining many variables into a single discriminant, allowing ATLAS to pull the faint signal of longitudinally polarised W bosons from the noise. This approach could only become more important as both datasets and physicists’ ambitions expand.

  Perhaps the broadest lesson in all this is that science often advances by the unglamorous task of verifying the details. The discovery of the Higgs boson answered one question but opened many others; among them, measuring how it affects the scattering of W bosons is one of the ore direct ways to probe whether the Standard Model is complete or just the first chapter of a longer story. Either way, the pursuit exemplifies the spirit of checking, rechecking, testing, and probing until scientists truly understand how nature works at extreme precision.

  Featured image: The massive mural of the ATLAS detector at CERN painted by artist Josef Kristofoletti. The mural is located at the ATLAS Experiment site and shows on two perpendicular walls the detector with a collision event superimposed. The event on the large wall shows a simulation of an event that would be recorded in ATLAS if a Higgs boson was produced. The cavern of the ATLAS Experiment with the detector is 100 m directly below the mural. The height of the mural is about 12 m. The actual ATLAS detector is more than twice as big. Credit: Claudia Marcelloni, Michael Barnett/CERN.

  2025.09.12

• Physicists test if they can load antimatter on a truck

  Physicists in Europe have reported that it’s possible to transport charged particles on a truck for four hours without disturbing them in any way. This seemingly run-of-the-mill announcement, reported in Nature on May 14, actually contains within its details the possibility of “a new era of precision antimatter spectroscopy”, in the team’s words.

  This is because of how the world currently studies antimatter, an elusive form of matter with some properties switched. For example, the electron’s antiparticle is the positron: it has the same mass but behaves like the electron’s mirror image. When a particle touches its antiparticle, they annihilate each other in a flash of energy.

  Physicists study antiparticles for what they can reveal about the still-mysterious things about our universe, such as dark matter. They’re also keen to crack the baryon asymmetry problem, which had a breakthrough reported on July 16.

  The problem is that antimatter is hard to produce in a machine made entirely of matter. What little scientists already know is based on studying antiprotons and atoms of hydrogen and helium made of antiprotons and positrons at the Antimatter Factory (AMF) at CERN, the European nuclear physics research facility more famous for hosting the Large Hadron Collider. Specifically, the problem is that AMF has instruments to study antiparticles but have limited sensitivity. Antimatter particles are also very sensitive to magnetic fields and the AMF hall has other instruments that emit such energy.

  In an ideal world, physicists should be able to produce antiparticles at AMF and transport it to a lab that has very good instruments to study them. The new study delivers a proof of concept showing this is now possible.

  At the heart of their effort is a Penning trap, a device that uses a combination of electric and magnetic fields to confine charged particles in a cylindrical tube. The magnetic field is uniform and flows through the cylinder’s central axis, holding the particles together like a string of beads. The electric field is quadrupole, like two positive and two negative charges forming a square shape with alternating charges at the vertices. This field keeps the particles from drifting away.

  In their truck, the physicists used a BASE-STEP Penning trap, a special kind of trap developed by the BASE collaboration at CERN. It’s a “Penning-trap system inside the bore of a superconducting magnet that can withstand transport-related forces.” Among other features, it uses cold beryllium ions to cool the stored particles and includes precision measurement techniques to study them.

  The team first moved a trap containing a cloud of around 100 protons out of the AMF hall using a pair of overhead cranes, then loaded it on a truck and drove 3.7 km through CERN’s Meyrin campus. They hit a maximum speed of 42.2 km/hr in this run.

  The setup included magnetic shielding and a “transport frame to handle acceleration forces apart from gravity of up to 1 g in all directions”, per the paper. On the truck, the apparatus was cooled by an “internal 30-litre liquid helium tank”. The precision voltage supply, frequency generators, and a spectrum analyser were run by a “UPS with two battery units”.

  In all, the device — 2 m long, 1.6 m tall, and 0.85 m wide — weighed about 900 kg.

  “In our future planned antiproton transport experiments,” the team wrote in its paper, “the last step in the transport campaign would be the extraction of a fraction of particles from the trapped antiproton reservoir, followed by the injection of the extracted fraction into a receiver experiment. Although we do not have such a receiver available yet, we have demonstrated particle separation and extraction after returning to the experiment zone.”

  The reason for going to all this trouble with a truck is an idea in physics called CPT symmetry. The material world is made of matter and all matter is made up of subatomic particles. While physicists know a lot about the material universe, there are still many unknowns and lots of room left for physicists to explore and learn. CPT symmetry is one corner of the room.

  Each letter stands for a kind of transformation. C (charge conjugation) means switching a particle with an antiparticle. P (parity) means switching left and right, like looking in a mirror. And T (time reversal) means reversing the flow of time. In quantum field theory (the tool physicists use to understand the physical properties of subatomic particles), CPT theorem states that if you applied all three operations to a particle, physics should be the same.

  That is to say, if you studied for a physics exam and then someone applied CPT to all particles in the universe, the answers to your question paper wouldn’t change.

  CPT symmetry has a sobering history. At the dawn of quantum field theory, scientists assumed all subatomic particles conserve C, P, and T symmetries separately. Then they found that wasn’t true, so they moved the goalpost and said all particles conserve CP symmetry. An experiment in 1964 challenged this as well when physicists found particles called kaons violated CP symmetry. Finally physicists moved the goalpost even further, saying that all subatomic particles should be expected to conserve CPT symmetry.

  Since the C part of the symmetry requires swapping a particle with its antiparticle, physicists need both matter and antimatter to check if particles obey or violate CPT symmetry. The more the merrier, too: larger quantities of antimatter will make it easier to tease out any subtle effects that might point to a violation. If all such subtlety can be ruled out, CPT symmetry will hold and physicists might breathe easier.

  In the truck study, of course, the physicists only used ~100 protons. “Although the number of stored particles was not pushed to the limit,” they explained, “the transported number would already be enough for our high-precision experiments to operate for several years. As an example, the non-destructive high-precision measurements performed in BASE … typically consume around six antiprotons per year.”

  So far, researchers have verified CPT symmetry conservation in anti-hydrogen (hydrogen atoms made of an antiproton and a positron) and anti-protonic helium (helium atoms with antiprotons). These are of course anti-atoms and are considered a type of particle called baryons.

  Baryons are the most well-known matter particles: they include protons and neutrons as well as all atoms. Your body, for example, is baryonic matter. Physicists are keen to crack the universe’s baryon asymmetry mystery, too — and the answer is expected to have to do with some particles violating CPT symmetry in a hitherto unknown way.

  The physicists wrote in their paper that their findings indicate the “next generation” of antiproton studies could reduce the uncertainty in measurements by a factor of 10 from the “present state of the art”.

  Featured image: Left: The route for the first transport demonstration through the AMF hall. Point 1 is the experiment zone from which an overhead crane moved the transport frame to point 2. At point 2, the transport frame was loaded onto a trailer and moved to point 3, where it then got picked up by the second overhead crane. Point 4 is the loading bay with the truck. Right: Road map of the Meyrin site of CERN and the GPS position data recorded during transportation. Credit: Nature 641, 871–875 (2025).

  2025.07.24

• Found: clue to crack the antimatter mystery

  Imagine you’ve put together a torchlight. You know exactly how each part of the device works. You know exactly how they’re all connected togetger. Yet when you put in fresh batteries and turn it on, the light flickers. You take the torchlight apart, check each component piece by piece. It’s all good. The batteries are fully charged as well. Then you put it back together and turn it — and the light flickers still.

  This torchlight is the Standard Model of particle physics. It’s the main theory of its field: it ties together the various properties of all the subatomic particles scientists have found thus far. It organises them into groups, describes how the groups interact with each other, and makes predictions about particles that have been tested to extraordinary precision. And yet, the Standard Model can’t explain what dark matter is, why the Higgs boson is so light or how neutrinos have mass.

  Physicists are thus looking for ‘new physics’: a hitherto unseen part of the torchlight’s internal apparatus that causes its light to flicker, i.e. some new particle or force that completes the Standard Model, closing the gaps that the current crop of particles and forces haven’t been able to.

  This search for new physics received a boost yesterday when the physicists working with one of the detectors of the Large Hadron Collider reported that they had observed CP violations in baryons. This phenomenon is required to explain why the universe has more matter than antimatter today even though it was assumed to have been born with equal quantities of both. Baryons are particles made up of three quarks, like protons and neutrons.

  CP symmetry is the idea that the laws of physics should be the same if you swap all particles with their antiparticles and flip left and right, like looking in a mirror. Thus CP violation in baryons means if swapped a baryon with the corresponding anti-baryon and swapped left and right, the laws of physics won’t be the same, i.e. the laws treat matter and antimatter differently.

  I wrote about this finding and its implications — including its place in the Sakharov conditions and what the results mean for the Standard Model — for The Hindu. Do read it.

  I’ve found it’s one of those things you don’t read because it has anything to say about saving money or living longer. By reminding you that there’s a natural universe out there worth exploring and discovering and that it contains no sign or imprint of the false justifications humans have advanced for their crimes, perhaps it can help you live better. As I’ve said before, if you’re not interested in particle physics, that’s fine. But remember that you can be.

  Featured image: A view of the LHCb detector at the LHC as seen through a fisheye lens. Credit: CERN.

  2025.07.17

• Technical foundation for a muon collider laid at J-PARC

  A particle collider is a machine that energises two beams of subatomic particles and smashes them head on.

  The Large Hadron Collider (LHC) in Europe is the world’s largest and most famous particle collider. It accelerates (with the effect of energising) two beams of protons to nearly the speed of light and has them collide. When they do, energy is released in the same way the collision of two cars releases sound, heat, and kinetic energy. The existing kinetic energy of the beams is redistributed into the mass and kinetic energy of new particles. By studying this process, physicists can learn a lot about their properties.

  For example, this is how they made one of the headline discoveries of the 21st century: the Higgs boson particle in 2012. Proving the particle exists allowed physicists to confirm that their theory about how subatomic particles get mass is right. That theory is in turn related to many properties of our universe, including its size, the formation of galaxies, and the inner lives of all the universe’s stars, including our sun. For first proposing that theory in 1964 (together with four others), Peter Higgs and François Englert were awarded the physics Nobel Prize in 2013.

  This said, the properties of the Higgs boson, which physicists have since examined in more detail, have raised more questions about the universe. Two examples include the mysterious nature of dark matter and why neutrinos have mass even though the theory that explains all subatomic particles says they shouldn’t.

  While scientists have built and are operating clever experiments to test different explanations for these anomalous entities, they are also discussing the possibility of building more powerful colliders. The LHC has been able to access a collision energy of up to 13.6 TeV, or about 14,000-times the energy of a proton at rest. Scientists are currently deliberating proposals for colliders that can do better.

  The machines in these proposals have taken three forms: a linear electron-positron collider, a circular electron-positron collider, and a circular proton-proton collider. Each of these machines will cost several billion dollars to build and will require many countries to fund and manage them.  So scientists have to be able to justify which collider they’d like to build and then convince governments to pay.

  The most common argument has been that participating in such sophisticated experiments will also lead to spin-off benefits that will give countries the edge in other spheres, including in medical diagnostics and materials of the future. Increasingly, the question of scientific leadership has also become relevant: India is looking for some of it en route to its goal to become an economically developed country by mid-century; the US is trying to not lose it to China; China is working to take more of it from the US; and so on.

  The point is that there is more at stake here than ‘simple’ problems in physics, although these questions are weighty in their own right.

  The problem currently is that all three types of machines — a linear/circular electron-positron collider or a circular proton-proton collider — are beset by important disadvantages of their own, and different scientists have focused on them (in addition to their price tags) as they try to decide the way forward.

  A circular proton-proton collider like the LHC but bigger can scale a collision energy of 100 TeV. However, it will need to deal with the fact that protons are composite particles, i.e. they’re made up of smaller particles. When they collide head on, only a small fraction of energy is used to ‘make’ new particles; the rest is exchanged between the constituent particles.

  Both electrons and positrons are elementary particles on the other hand and generate ‘clean’ collision data. But when an electron (or a positron) is circulated in a magnetic field through the collider while it’s being accelerated, its small mass means it releases much of the energy it acquires as light. Thus circular electron accelerators consume a lot of energy to achieve their results.

  

  A linear collider doesn’t have this problem since the particles are accelerated in a straight line, but because they can’t go round and round to accelerate more and more, the machine needs to be really long. In some designs they are a few tens of kilometres long: finding a suitably large patch of land is difficult, and maintaining the integrity of the beam across that distance more so. And because each group of particles collides only once and is dumped, the collider must produce, accelerate, and dispose of fresh ultra-intense particle beams at a high frequency, increasing its wall-plug power demand.

  In this scenario, some scientists are also mulling a new type of collider that hasn’t been built before — one for muons. Unlike protons and like electrons, muons are elementary particles and thus lead to clean collisions. A muon is also about 200-times heavier than an electron, so it loses more than a billion-times less energy as light when it’s being accelerated in a circle.

  Thus, as scientist Diktys Stratakis of Fermilab in the US wrote, “A muon collider ring with a circumference of 10 km could have the same potential as a 100 km proton collider ring, if proven to be feasible.”

  But of course it’s not a silver bullet. Perhaps the single biggest issue is that muons are much less stable than protons or electrons. Each muon has a lifetime of about 2.2 microseconds at rest. So producing a sufficiently dense bunch of muons is difficult. The collider must also be able to create large, powerful magnetic fields fast enough before the muons decay. And when muons do decay, they emit electrons or positrons that the machine’s various components must be shielded from. So building a muon collider entails a lot of innovation first.

  A team of scientists in Japan recently reported in Physical Review Letters that they had taken a crucial step forward: they were able to cool (de-energise) a bunch of muons, then accelerate them for the first time using a device called a radiofrequency cavity. This is significant because this end-to-end feat has never been demonstrated before and as such represents the first major problem to solve when building a muon collider.

  The scientists — from Canada, China, and Japan — performed their feat at the Japan Proton Accelerator Research Complex (J-PARC) in Tokai. They achieved it in six steps.

  1. A beam of 0.003 TeV protons strikes a graphite target and produces ‘hot’ muons.

  2. A slender aluminium foil in front of the target slows them down a little.

  3. The muons are further slowed by an 8-mm thick silicon dioxide aerogel disc. As a muon slows nearly to a halt, it bonds with an electron in the aerogel to create a muonium atom: a positively charged muon plus a negatively charged electron.

  4. An ultraviolet laser knocks off the electrons to free very low energy muons — about as much energy they’d have at room temperature.

  5. Electrostatic lenses and steering plates impart a small amount of energy to the muons and focus them, like getting people at a venue to gather in a single room.

  6. The muons are subjected to electric fields alternating at 324 MHz inside a 3-m-long tube, accelerating them. (This is the radiofrequency stage.)

  The feat is the first ever demonstration that started with muons jiggling around at a room-temperature level of energy (around 25 meV) and ended with muons moving in a common direction with about 100 keV of energy — an energy boost by a factor of 4 million.

  

  While 100 keV is still seven orders of magnitude away from 2 TeV, the Japan team’s feat is remarkable because it ‘solves’ the very first and possibly  hardest challenge presented by a muon collider: catching ‘live’ muons before they ‘die’. The team’s setup stopped fast-moving muons, cooled them to 25 meV, stripped the electrons, and injected them into a radiofrequency cavity in 2.28 microseconds, i.e. within the muons’ lifetime. In a manner of speaking, if a 2-TeV muon collider is a skyscraper, the study lays the foundation.

  The J-PARC team was also able to cut the transverse emittance — a measure of how the beam spreads — by 200-times horizontally and 400-times vertically relative to the raw muon beam at the beginning. This two-order-of-magnitude reduction is paramount for the lightly energised muon beam to enter the next, more powerful accelerators.

  “Although the beam produced by the J-PARC team is of good quality (in terms of having low emittance), its energy and intensity are not yet high enough for the experiments that researchers eventually hope to make. Nevertheless, the demonstration of the potential to re-accelerate cold muons is an exciting step forward,” Chris Rogers, a scientist with the ISIS Neutron and Muon Source at the Rutherford Appleton Laboratory in the UK, wrote in Physics.

  Featured image: All matter around us is made of elementary particles, the building blocks of matter. These particles occur in two basic types called quarks and leptons. Each group consists of six particles, which are related in pairs, or ‘generations’. The muon is a type of lepton, denoted by the letter µ. Credit: CERN.

  2025.06.24

• “Who are we?”

  From ‘‘The physics community has never split like this’: row erupts over plans for new Large Hadron Collider’, The Guardian, March 29, 2025:

  However, if the FCC were given the go-ahead, it could lock up funds for decades and end up dictating the direction that particle physics will have to take for much of the century, [DESY Hamburg researcher Jenny] List added. “We will be telling future generations exactly what to do scientifically, and so we need to ask ourselves today: who are we to decide what our grandchildren should research and not research?”

  What a powerful argument. And it cuts both ways, too: just as much as we must acknowledge the risks of “locking in” scientists to the FCC while starving other avenues of particle physics research of funds, there is also a well-defined risk in missing a window to fund the FCC while it’s open instead of waiting and losing a potentially one-time opportunity.

  In an ideal world, physicists may like to pursue as many avenues as possible (towards developing a unified and complete description of the physical universe). Of course, more avenues will be possible if they give up on the FCC and split the money they save to hundreds more of smaller projects. But I think it’s also possible to argue building the FCC will itself push physics research in many new directions, providing answers no other experiment can to inform and guide more research. The sword really does cut both ways.

  Even in terms of funding: while giving up on the FCC will ‘spare’ funds that could serve many smaller experiments well, there’s no telling if governments will make them just as available for the latter and, equally, if the political will among governments to fund an FCC-like machine will always exist. The language around the FCC’s budgeting is also confusing: its $30 billion (Rs 2.56 lakh crore) cost will be spent over decades, not in one shot, and a not insignificant chunk of these expenses will be in the form of people’s work-hours and components manufactured by industrial centres in various participating countries.

  Which is why I think the question “who are we to decide?” sounds like a cop-out. Fundamentally, who else is going to decide? Physicists need to make decisions now. It’s likely very difficult for anyone to say if the decision they make at this time will be the right one. All that’s clear is that they need to decide. In fact, we need to decide, going by what IIT Mandi physicist Nirmalya Kajuri wrote in The Wire Science in 2019:

  Irrespective of which way the debate swings, it has already shown that the few who communicate science can have a lopsided influence on the public perception of an entire field – even if they’re not from that field. The distinction between a particle physicist and, say, a condensed-matter physicist is not as meaningful to most people reading the New York Times or any other mainstream publication as it is to physicists. There’s no reason among readers to exclude [Sabine] Hossenfelder as an expert.

  However, very few physicists engage in science communication. The extreme ‘publish or perish’ culture that prevails in sciences means that spending time in any activity other than research carries a large risk. In some places, in fact, junior scientists spending time popularising science are frowned upon because they’re seen to be spending time on something unproductive. But debates like this demonstrate the rewards of science communication.

  2025.03.29

• “Why has no Indian won a science Nobel this year?”

  For all their flaws, the science Nobel Prizes – at the time they’re announced, in the first week of October every year – provide a good opportunity to learn about some obscure part of the scientific endeavour with far-reaching consequences for humankind. This year, for example, we learnt about attosecond physics, quantum dots, and in–vitro transcribed mRNA. The respective laureates had roots in Austria, France, Hungary, Russia, Tunisia, and the U.S. Among the many readers that consume articles about these individuals’ work with any zest, the science Nobel Prizes’ announcement is also occasion for a recurring question: how come no scientist from India – such a large country, of so many people with diverse skills, and such heavy investments in research – has won a prize? I thought I’d jot down my version of the answer in this post. There are four factors:

  1. Missing the forest for the trees – To believe that there’s a legitimate question in “why has no Indian won a science Nobel Prize of late?” is to suggest that we don’t consider what we read in the news everyday to be connected to our scientific enterprise. Pseudoscience and misinformation are almost everywhere you look. We’re underfunding education, most schools are short-staffed, and teachers are underpaid. R&D allocations by the national government have stagnated. Academic freedom is often stifled in the name of “national interest”. Students and teachers from the so-called ‘non-upper-castes’ are harassed even in higher education centres. Procedural inefficiencies and red tape constantly delay funding to young scholars. Pettiness and politicking rule many universities’ roosts. There are ill-conceived limits on the use, import, and export of biological specimens (and uncertainty about the state’s attitude to it). Political leaders frequently mock scientific literacy. In this milieu, it’s as much about having the resources to do good science as being able to prioritise science.

  2. Historical backlog – This year’s science Nobel Prizes have been awarded for work that was conducted in the 1980s and 1990s. This is partly because the winning work has to have demonstrated that it’s of widespread benefit, which takes time (the medicine prize was a notable exception this year because the pandemic accelerated the work’s adoption), and partly because each prize most often – but not always – recognises one particular topic. Given that there are several thousand instances of excellent scientific work, it’s possible, on paper, for the Nobel Prizes to spend several decades awarding scientific work conducted in the 20th century alone. Recall that this was a boom time for science, with the advent of quantum mechanics and the theories of relativity, considerable war-time investment and government support, followed by revolutions in electronics, materials science, spaceflight, genetics, and pharmaceuticals, and then came the internet. It was also the time when India was finding its feet, especially until economic liberalisation in the early 1990s.

  3. Lack of visibility of research – Visibility is a unifying theme of the Nobel laureates and their work. That is, you need to do good work as well as be seen to be doing that work. If you come up with a great idea but publish it in an obscure journal with no international readership, you will lose out to someone who came up with the same idea but later, and published it in one of the most-read journals in the world. Scientists don’t willingly opt for obscure journals, of course: publishing in better-read journals isn’t easy because you’re competing with other papers for space, the journals’ editors often have a preference for more sensational work (or sensationalisable work, such as a paper co-authored by an older Nobel laureate; see here), and publishing fees can be prohibitively high. The story of Meghnad Saha, who was nominated for a Nobel Prize but didn’t win, offers an archetypal example. How journals have affected the composition of the scientific literature is a vast and therefore separate topic, but in short, they’ve played a big part to skew it in favour of some kinds of results over others – even if they’re all equally valuable as scientific contributions – and to favour authors from some parts of the world over others. Journals’ biases sit on top of those of universities and research groups.

  4. Award fixation – The Nobel Prizes aren’t interested in interrogating the histories and social circumstances in which science (that it considers to be prize-worthy) happens; they simply fete what is. It’s we who must grapple with the consequences of our histories of science, particularly science’s relationship with colonialism, and make reparations. Fixating on winning a science Nobel Prize could also lock our research enterprise – and the public perception of that enterprise – into a paradigm that prefers individual winners. The large international collaboration is a good example: When physicists working with the LHC found the Higgs boson in 2012, two physicists who predicted the particle’s existence in 1964 won the corresponding Nobel Prize. Similarly, when scientists at the LIGO detectors in the US first observed gravitational waves in 2016, three physicists who conceived of LIGO in the 1970s won the prize. Yet the LHC and the LIGOs, and other similar instruments continue to make important contributions to science – directly, by probing reality, and indirectly by supporting research that can be adapted for other fields. One 2007 paper also found that Nobel Prizes have been awarded to inventions only 23% of the time. Does that mean we should just focus on discoveries? That’s a silly way of doing science.

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  The Nobel Prizes began as the testament of a wealthy Swedish man who was worried about his legacy. He started a foundation that put together a committee to select winners of some prizes every year, with some cash from the man’s considerable fortunes. Over the years, the committee made a habit of looking for and selecting some of the greatest accomplishments of science (but not all), so much so that the laureates’ standing in the scientific community created an aspiration to win the prize. Many prizes begin like the Nobel Prizes did but become irrelevant because they don’t pay enough attention to the relationship between the laureate-selecting process and the prize’s public reputation (note that the Nobel Prizes acquired their reputation in a different era). The Infosys Prize has elevated itself in this way whereas the Indian Science Congress’s prize has undermined itself. India or any Indian for that matter can institute an award that chooses its winners more carefully, and gives them lots of money (which I’m opposed to vis-à-vis senior scientists) to draw popular attention.

  There are many reasons an Indian hasn’t won a science Nobel Prize in a while but it’s not the only prize worth winning. Let’s aspire to other, even better, ones.

  2023.10.06

• New LHC data puts ‘new physics’ lead to bed

  One particle in the big zoo of subatomic particles is the B meson. It has a very short lifetime once it’s created. In rare instances it decays to three lighter particles: a kaon, a lepton and an anti-lepton. There are many types of leptons and anti-leptons. Two are electrons/anti-electrons and muons/anti-muons. According to the existing theory of particle physics, they should be the decay products with equal probability: a B meson should decay to a kaon, electron and anti-electron as often as it decays to a kaon, muon and anti-muon (after adjusting for mass, since the muon is heavier).

  In the last 13 years, physicists studying B meson decays had found on four occasions that it decayed to a kaon, electron and anti-electron more often. They were glad for it, in a way. They had worked out the existing theory, called the Standard Model of particle physics, from the mid-20th century in a series of Nobel Prize-winning papers and experiments. Today, it stands complete, explaining the properties of a variety of subatomic particles. But it still can’t explain what dark matter is, why the Higgs boson is so heavy or why there are three ‘generations’ of quarks, not more or less. If the Standard Model is old physics, particle physicists believe there could be a ‘new physics’ out there – some particle or force they haven’t discovered yet – which could really complete the Standard Model and settle the unresolved mysteries.

  Over the years, they have explored various leads for ‘new physics’ in different experiments, but eventually, with more data, the findings have all been found to be in line with the predictions of the Standard Model. Until 2022, the anomalous B meson decays were thought to be a potential source of ‘new physics’ as well. A 2009 study in Japan found that some B meson decays created electron/anti-electrons pairs more often than muons/anti-muon pairs – as did a 2012 study in the US and a 2014 study in Europe. The last one involved the Large Hadron Collider (LHC), operated by the European Organisation for Nuclear Research (CERN) in France, and a detector on it called LHCb. Among other things, the LHCb tracks B mesons. In March 2021, the LHCb collaboration released data qualitatively significant enough to claim ‘evidence’ that some B mesons were decaying to electron/anti-electron pairs more often than to muon/anti-muon pairs.

  But the latest data from the LHC, released on December 20, appears to settle the question: it’s still old physics. The formation of different types of lepton/anti-lepton particle pairs with equal probability is called lepton-flavour universality. Since 2009, physicists had been recording data that suggested that one type of some B meson decays were violating lepton-flavour university, in the form of a previously unknown particle or force acting on the decay process. In the new data, physicists analysed B meson decays in the current as well as one of two other pathways, and at two different energy levels – thus, as the official press release put it, “yielding four independent comparisons of the decays”. The more data there is to compare, the more robust the findings will be.

  This data was collected over the last five years. Every time the LHC operates, it’s called a ‘run’. Each run generates several terabytes of data that physicists, with the help of computers, comb through in search of evidence for different hypotheses. The data for the new analysis was collected over two runs. And it led physicists to conclude that B mesons’ decay does not violate lepton-flavour universality. The Standard Model still stands and, perhaps equally importantly, a 13-year-old ‘new physics’ lead has been returned to dormancy.

  The LHC is currently in its third run; scientists and engineers working with the machine perform maintenance and install upgrades between runs, so each new cycle of operations is expected to produce more as well as more precise data, leading to more high-precision analyses that could, physicists hope, one day reveal ‘new physics’.

  2022.12.20

• Science’s humankind shield

  We need to reconsider where the notion that “science benefits all humans” comes from and whether it is really beneficial.

  I was prompted to this after coming upon a short article in Sky & Telescope about the Holmdel Horn antenna in New Jersey being threatened by a local redevelopment plan. In the 1960s, Arno Penzias and Robert Wilson used the Holmdel Horn to record the first observational evidence of the cosmic microwave background, which is radiation leftover from – and therefore favourable evidence for – the Big Bang event. In a manner of speaking, then, the Holmdel Horn is an important part of the story of humans’ awareness of their place in the universe.

  The US government designated the site of the antenna a ‘National Historic Landmark’ in 1989. On November 22, 2022, the Holmdel Township Committee nonetheless petitioned the planning board to consider redeveloping the locality where the antenna is located. According to the Sky & Telescope article, “If the town permits development of the site, most likely to build high-end residences, the Horn could be removed or even destroyed. The fact that it is a National Historic Landmark does not protect it. The horn is on private property and receives no Federal funds for its upkeep.” Some people have responded to the threat by suggesting that the Holmdel Horn be moved to the sprawling Green Bank Telescope premises in Virginia. This would separate it from the piece of land that can then be put to other use.

  Overall, based on posts on Twitter, the prevailing sentiment appears to be that the Holmdel Horn antenna is a historic site worthy of preservation. One commenter, an amateur astronomer, wrote under the article:

  “The Holmdel Horn Antenna changed humanity’s understanding of our place in the universe. The antenna belongs to all of humanity. The owners of the property, Holmdel Township, and Monmouth County have a historic responsibility to preserve the antenna so future generations can see and appreciate it.”

  (I think the commenter meant “humankind” instead of “humanity”.)

  The history of astronomy involved, and involves, thousands of antennae and observatories around the world. Even with an arbitrarily high threshold to define the ‘most significant’ discoveries, there are likely to be hundreds (if not more) of facilities that made them and could thus be deemed to be worthy of preservation. But should we really preserve all of them?

  Astronomers, perhaps among all scientists, are likelier to be most keenly aware of the importance of land to the scientific enterprise. Land is a finite resource that is crucial to most, if not all, realms of the human enterprise. Astronomers experienced this firsthand when the Indigenous peoples of Hawai’i protested the construction of the Thirty Meter Telescope on Mauna Kea, leading to a long-overdue reckoning with the legacy of telescopes on this and other landmarks that are culturally significant to the locals, but whose access to these sites has come to be mediated by the needs of astronomers. In 2020, Nithyanand Rao wrote an informative article about how “astronomy and colonialism have a shared history”, with land and access to clear skies as the resources at its heart.

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  Also read:

  • Immunity for scientists? Err…
  • Should ‘geniuses’ be paid extra?

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  One argument that astronomers arguing in favour of building or retaining these controversial telescopes have used is to claim that the fruits of science “belong to all of humankind”, including to the locals. This is dubious in at least two ways.

  First, are the fruits really accessible to everyone? This doesn’t just mean the papers that astronomers publish based on work using these telescopes are openly and freely available. It also requires that the topics that astronomers work on need to be based on the consensus of all stakeholders, not just the astronomers. Also, who does and doesn’t get observation time on the telescope? What does the local government expect the telescope to achieve? What are the sorts of studies the telescope can and can’t support? Are the ground facilities equally accessible to everyone? There are more questions to ask, but I think you get the idea that claiming the fruits of scientific labour – at least astronomic labour – are available to everyone is disingenuous simply because there are many axes of exclusion in the instrument’s construction and operation.

  Second, who wants a telescope? More specifically, what are the terms on which it might be fair for a small group of people to decide what “all of humankind” wants? Sure, what I’m proposing sounds comical – a global consensus mechanism just to make a seemingly harmless statement like “science benefits everyone” – but the converse seems equally comical: to presume benefits for everyone when in fact they really accrue to a small group and to rely on self-fulfilling prophecies to stake claims to favourable outcomes.

  Given enough time and funds, any reasonably designed international enterprise, like housing development or climate financing, is likely to benefit humankind. Scientists have advanced similar arguments when advocating for building particle supercolliders: that the extant Large Hadron Collider (LHC) in Europe has led to advances in medical diagnostics, distributed computing and materials science, apart from confirming the existence of the Higgs boson. All these advances are secondary goals, at best, and justify neither the LHC nor its significant construction and operational costs. Also, who’s to say we wouldn’t have made these advances by following any other trajectory?

  Scientists, or even just the limited group of astronomers, often advance the idea that their work is for everyone’s good – elevating it to a universally desirable thing, propping it up like a shield in the face of questions about whether we really need an expensive new experiment – whereas on the ground its profits are disseminated along crisscrossing gradients, limited by borders.

  I’m inclined to harbour a similar sentiment towards the Holmdel Horn antenna in the US: it doesn’t belong to all of humanity, and if you (astronomers in the US, e.g.) wish to preserve it, don’t do it in my name. I’m indifferent to the fate of the Horn because I recognise that what we do and don’t seek to preserve is influenced by its significance as an instrument of science (in this case) as much as by ideas of national prestige and self-perception – and this is a project in which I have never had any part. A plaque installed on the Horn reads: “This site possesses national significance in commemorating the history of the United States of America.”

  I also recognise the value of land and, thus, must acknowledge the significance of my ignorance of the history of the territory that the Horn currently occupies as well as the importance of reclaiming it for newer use. (I am, however, opposed in principle to the Horn being threatened by the prospect of “high-end residences” rather than affordable housing for more people.) Obviously others – most others, even – might feel differently, but I’m curious if a) scientists anywhere, other than astronomers, have ever systematically dealt with push-back along this line, and b) the other ways in which they defend their work at large when they can’t or won’t use the “benefits everyone” tack.

  2022.12.11

• What arguments against the ‘next LHC’ say about funding Big Physics

  A few days ago, a physicist (and PhD holder) named Thomas Hartsfield published a strange article in Big Think about why building a $100-billion particle physics machine like the Large Hadron Collider (LHC) is a bad idea. The article was so replete with errors things that even I – a not-physicist and not-a-PhD-holder – cringed reading them. I also wanted to blog about the piece but theoretical physicist Matthew Strassler beat me to it, with a straightforward post about the many ways in which Hartsfield’s article was just plain wrong, especially coming from a physicist. But I also think there were some things that Strassler either overlooked or left unsaid and which to my mind bear fleshing out – particularly points that have to do with the political economy of building research machines like the LHC. I also visit in the end the thing that really made me want to write this post, in response to a seemingly throwaway line in Strassler’s post. First, the problems that Hartsfield’s piece throws up and which deserve more attention:

  1. One of Hartsfield’s bigger points in his article is that instead of spending $100 billion on one big physics project, we could spend it on 100,000 smaller projects. I agree with this view, sensu lato, that we need to involve more stakeholders than only physicists when contemplating the need for the next big accelerator or collider. However, in making the argument that the money can be redistributed, Hartsfield presumes that a) if a big publicly funded physics project is cancelled, the allocated money that the government doesn’t spend as a result will subsequently be diverted to other physics prohects, and b) this is all the money that we have to work with. Strassler provided the most famous example of the fallacy pertinent to (a): the Superconducting Super Collider in the US, whose eventually cancellation ‘freed’ an allocation of $4.4 billion, but the US government didn’t redirect this money back into other physics research grants. (b), on the other hand, is a more pernicious problem: a government allocating $100 billion for one project does not implicitly mean that it can’t spare $10 million for a different project, or projects. Realpolitik is important here. Politicians may contend that after having approved $100 billion for one project, it may not be politically favourable for them to return to Congress or Parliament or wherever with another proposal for $10 million. But on the flip side, both mega-projects and many physics research items are couched in arguments and aspirations to improve bilateral or multilateral ties (without vomiting on other prime ministers), ease geopolitical tensions, score or maintain research leadership, increase research output, generate opportunities for long-term technological spin-offs, spur local industries, etc. Put another way, a Big Science project is not just a science project; depending on the country, it could well be a national undertaking along the lines of the Apollo 11 mission. These arguments matter for political consensus – and axiomatically the research projects that are able to present these incentives are significantly different from those that aren’t, which in turn can help fund both Big Science and ‘Small Science’ projects at the same time. The possibility exists. For example, the Indian government has funded Gaganyaan separately from ISRO’s other activities. $100 billion isn’t all the money that’s available, and we should stop settling for such big numbers when they are presented to us.

  2. These days, big machines like the one Hartsfield has erected as a “straw man” – to use Strassler words – aren’t built by individual countries. They are the product of an international collaboration, typically with dozens of governments, hundreds of universities and thousands of researchers participating. The funds allocated are also spent over many years, even decades. In this scenario, when a $100-billion particle collider is cancelled, no one entity in the whole world suddenly has that much money to give away at any given moment. Furthermore, in big collaborations, countries don’t just give money; often they add value by manufacturing various components, leasing existing facilities, sharing both human and material resources, providing loans, etc. The value of each of these contracts is added to the total value of the project. For example, India has been helping the LHC by manufacturing and supplying components related to the machine’s magnetic and cryogenic facilities. Let’s say India’s Departments of Science and Technology and of Atomic Energy had inked contracts with CERN, which hosts and maintains the LHC, worth $10 million to make and transport these components, but then the LHC had been called off just before its construction was to begin. Does this mean India would have had $10 million to give away to other science projects? Not at all! In fact, manufacturers within the country would have been bummed about losing the contracts.

  3. Hartsfield doesn’t seem to acknowledge incremental results, results that improve the precision of prior measurements and results that narrow the range in which we can find a particle. Instead, he counts only singularly positive, and sensational, results – of which the LHC has had only one: the discovery of the Higgs boson in 2012. Take all of them together and the LHC will suddenly seem more productive. Simply put, precision-improving results are important because even a minute difference between the theoretically predicted value and the observed value could be a significant discovery that opens the door to ‘new physics’. We recently saw this with the mass of a subatomic particle called the W boson. Based on the data collected by a detector mounted on the Tevatron particle accelerator in Illinois, physicists found that the mass of the W boson differed from the predicted value by around 0.12%. This was sufficient to set off a tsunami of excitement and speculation in the particle physics community. (Hartsfield also overlooked an important fact and which Strassler caught: that the LHC collects a lot more data than physicists can process in a single year, which means that when the LHC winds down, physicists will still have many years of work left before they are done with the LHC altogether. This is evidently still happening with the Tevatron, which was shut down in 2011, so Hartsfield missing it is quite weird. Another thing that happened to Tevatron and is still happening with the LHC is that these machines are upgraded over time to produce better results.) Similarly, results that exclude the energy ranges in which a particle can be found are important because they tell us what kind of instruments we should build in future to detect the same particle. We obviously won’t need instruments that sweep the same energy range (nor will we have a guarantee that the particle will be found outside the excluded energy range – that’s a separate problem). There is another point to be made but which may not apply to CERN as much as to Big Science projects in other countries: one country’s research community building and operating a very large research facility signals to other countries that the researchers know what they’re doing and that they might be more deserving of future investments than other candidates with similar proposals. This is one of the things that India lost with the scuttling of the India-based Neutrino Observatory (the loss itself was deserved, to be sure).

  Finally, the statement in Strassler’s post that piqued me the most:

  My impression, from his writing and from what I can find online, is that most of what he knows about particle physics comes from reading people like Ethan Siegel and Sabine Hossenfelder. I think Dr. Hartsfield would have done better to leave the argument to them.

  Thomas Hartsfield has clearly done a shoddy job in his article in the course of arguing against a Big Physics machine like LHC in the future, but his screwing up doesn’t mean discussions on the need for the next big collider should be left to physicists. I admit that Strassler’s point here was probably limited to the people whose articles and videos were apparently Hartsfield’s primary sources of information – but it also seemed to imply that instead of helping those who get things wrong do better next time, it’s okay to ask them to not try again and instead leave the communication efforts to their primary sources. That’s Ethan Siegel and Sabine Hossenfelder in this case – both prolific communicators – but in many instances, bad articles are written by writers who bothered to try while their sources weren’t doing more or better to communicate to the people at large. This is also why it bears repeating that when it comes to determining the need for a Big Physics project of the likes of the LHC, physics is decidedly one non-majority part of it and that – importantly – science communicators also have an equally vital role to play. Let me quote here from an article by physicist Nirmalya Kajuri, published in The Wire Science in February 2019:

  … the few who communicate science can have a lopsided influence on the public perception of an entire field – even if they’re not from that field. The distinction between a particle physicist and, say, a condensed-matter physicist is not as meaningful to most people reading the New York Times or any other mainstream publication as it is to physicists. There’s no reason among readers to exclude [one physicist] as an expert.

  However, very few physicists engage in science communication. The extreme ‘publish or perish’ culture that prevails in sciences means that spending time in any activity other than research carries a large risk. In some places, in fact, junior scientists spending time popularising science are frowned upon because they’re seen to be spending time on something unproductive.

  …

  All physicists agree that we can’t keep building colliders ad infinitum. They differ on when to quit. Now would be a good time, according to Hossenfelder. Most particle physicists don’t think so. But how will we know when we’ve reached that point? What are the objective parameters here? These are complex questions, and the final call will be made by our ultimate sponsors: the people.

  So it’s a good thing that this debate is playing out before the public eye. In the days to come, physicists and non-physicists must continue this dialogue and find mutually agreeable answers. Extensive, honest science communication will be key.

  So more physicists should join in the fray, as should science journalists, writers, bloggers and communicators in general. Just that they should also do better than Thomas Hartsfield to get the details right.

  2022.06.10