Tag: Sabine Hossenfelder

• String theory and reconciliations

  According to particle physics, the fundamental building blocks of the universe are point-like particles, essentially small dots of energy with no dimension. String theory posits that these dots are actually minuscule vibrating loops of energy. A violin string vibrating at different frequencies produces different musical notes; similarly these filaments are said to be able to vibrate at different frequencies, each one creating a different particle of our universe. One note is an electron, another is a photon, and so on.

  String theory hasn’t been proven — it hasn’t made any testable predictions so far, in fact. Yet it exists because scientists are looking for a ‘theory of everything’: a single theory that can explain both gravity and quantum physics. At present these two theories together explain their particular domains very well but scientists don’t know how they fit together. String theory is one of a few theory programmes trying to reconcile them; others include loop quantum gravity and twistor theory.

  On January 7, scientists from Hungary, Israel, and the US published a curious paper in Nature. Stumped by the complex shapes of neurons, they reportedly found a solution in some arcane equations in string theory and, according to them, the equations also describe how blood vessels and neurons branch.

  If you were an engineer designing the wiring for a brain or a vascular system, you’d probably try to save money by using the least amount of wire possible. For a long time, biologists assumed nature ‘thought’ the same way. According to this paper, however, it doesn’t, at least not necessarily. The researchers analysed high-resolution 3D scans of neurons, blood vessels, and fungi and showed that biological networks don’t care about minimising length but about minimising surface area. And to figure out the complex geometry of how these tubelike structures connect, the researchers borrowed the maths of interacting strings.

  The scientific method says that if you can’t prove something with an experiment, it isn’t science. The problem for string theory is that it describes a part of space so small and so fleeting that no machine we can currently build could ever study it. Yet many physicists have stuck with it because, even though it remains entirely mathematical, they’ve glimpsed deep connections between its equations and structures and other branches of mathematics and physics. According to the physicists these connections are signs that string theory contains ‘truths’ worth exploring more and due to which it can’t simply be dismissed out of hand.

  On the other hand we also have scientists like Peter Woit who have lamented, repeatedly, that string theory is a dead-end, that despite all of its mathematical elegance and structure the fact that it hasn’t made a testable prediction, and doesn’t seem like it will for the foreseeable future, it’s been a drain on physicists’ time and intelligence. Over the years however, neither side has been able to persuade or dissuade the other, and today many criticisms have hardened into denial and vitriol.

  Stockholm University philosopher Richard Dawid published a provocative book in 2013 that, despite its seemingly reconciliatory premise, entrenched these divisions. In the text, titled String Theory and the Scientific Method, based on a small conference he’d conducted a short while earlier, Dawid argued that the history of science is witness to a revolution in how scientific truth can be redefined. (American philosopher and biologist Massimo Pigliucci’s essay in Aeon on the conference and how philosophy can help with science’s demarcation problem is also worth a read.) He proposed that in the absence of empirical data, experts must rely on non-empirical evidence, like the sheer mathematical elegance of a theory or the fact that no one can find a better alternative. That is, he seemed to say, a theory could be true because it’s too ‘good’ to be wrong.

  I’m partial to criticisms of the book, especially those advanced by George Ellis, Joe Silk, Sabine Hossenfelder, and Carlo Rovelli, rather than the book itself.

  Ellis and Silk, both cosmologists, argued that Dawid’s push for “non-empirical theory assessment” (which he prefers to “post-empirical science”) is dangerous for suggesting that a theory can be validated by its ‘elegance’ or its power to explain something post facto. The danger here is that if you move these goalposts you also let in pseudoscience. Hossenfelder, a physicist, took aim at Dawid’s argument that string theory must be true because scientists haven’t found another option that’s equally good. According to her, claiming there are no alternatives is a sociological observation rather than scientific proof, i.e. that scientists can’t imagine an alternative today doesn’t mean one doesn’t exist. It may simply be a lack of imagination, of funding for rival approaches or even of groupthink within the academic community.

  Third, Rovelli, also a physicist and a cofounder of loop quantum gravity, argued that the history of science is littered with beautiful, mathematically coherent theories that turned out to be wrong. He also posited that Dawid’s “unexpected explanatory coherence”, i.e. when a theory solves problems it wasn’t built to solve, is often a result of confirmation bias and that once a community is deeply invested in a mathematical framework, it will inevitably find internal connections that look ‘miraculous’ but have no bearing on physical reality.

  Hossenfelder’s and Rovelli’s criticisms also help to see the problems with using the new Nature paper to claim it verifies or legitimises the pursuit of string theory in any meaningful way. Its authors show that the mathematics of string theory handles problems in which you need to minimise the surface area very well, but this shouldn’t be surprising, as Rovelli has argued. Complex maths is often useful in disparate fields but just because calculus describes both the orbit of planets and the marginal cost of gizmos doesn’t mean gravity holds the economy together.

  Similarly, that string theory describes the branching of neurons doesn’t mean the universe is fundamentally made of vibrating strings. The only way to know the latter is if the theory unifies the principles of quantum mechanics with gravity and makes a testable prediction.

  The paper’s authors themselves, while taking care to temper their claims regarding the physical reality of string theory, have also expressed optimism about its mathematical necessity. They’ve called their finding a “formal mapping between surface minimisation and high-dimensional Feynman diagrams” and say they’re taking “advantage of a well-developed string-theoretical toolset”. They also clarify that they’re removing the fundamental physical properties usually associated with string theory as a ‘theory of everything’ and instead treating the matter at hand as a very difficult geometry problem. Then, however, they strongly imply that the mathematics of string theory is essential to solving this problem.

  Now, is it possible to reconcile the (demonstrated) usefulness of the string theory toolkit with Rovelli’s and Hossenfelder’s criticisms? Specifically, setting aside for a moment the fact that the new study treats the maths of string theory as a toolkit: while solving the problem doesn’t ‘prove’ string theory in any meaningful way, how does one reconcile the notion that string theorists indeed developed this mathematical toolkit with Rovelli’s criticism? Is it possible to argue that only string theory could have discovered this toolkit despite Hossenfelder’s criticisms or is it possible to conclude in a reasonable way that we simply use the complex mathematics and discard the rest?

  I think this entails distinguishing between the mathematical machinery and the physical claims. Rovelli’s position isn’t that string theory mathematics are ‘wrong’ or ‘useless’ but rather that internal consistency and mathematical elegance alone don’t constitute empirical proof of quantum gravity. So the fact that string theorists developed a toolkit that can solve problems in biology doesn’t contradict Rovelli, in fact it arguably supports his view that string theory has become a rich mathematical framework. The act of reconciliation lies here in accepting that string theorists spent decades exploring the geometry of interacting surfaces (which they call “worldsheets”).

  Second, vis-à-vis Hossenfelder’s pushback to Dawid’s argument that there are no equally good alternatives to string theory, it also seems physically as well as historically risky to argue that only string theory could have discovered these tools. A mathematician focusing purely on topology or differential geometry could likely have arrived at similar tools without positing 10 dimensions or supersymmetry. In this sense string theory has simply been a historical catalyst, an ‘engine’ that seems to have accelerated humans’ approach to the toolkit that they subsequently used to solve a particular problem in brain biology.

  I’m generally wary of non-empirical assertions, so perhaps a scientifically robust position for me to take is the instrumentalist rather than the realist view: i.e. to conclude we can use the mathematics and discard the physical dogma. This way I retain the formalism, which is the calculus of optimising 3D surfaces, because it works for the data, while rejecting the ontology, i.e. the idea that the universe is fundamentally composed of strings.

  2026.01.15

• “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

• On resource constraints and merit

  In the face of complaints about how so few women have been awarded this year’s Swarnajayanti Fellowships in India, some scientists pushed back asking which of the male laureates who had been selected should have been left out instead.

  This is a version of the merit argument commonly applied to demands for reservation and quota in higher education – and it’s also a form of an argument that often raises its head in seemingly resource-constrained environments.

  India is often referred to as a country with ‘finite’ resources, often when people are discussing how best to put these resources to use. There are even romantic ideals associated with working in such environments, such as doing more with less – as ISRO has been for many decades – and the popular concept of jugaad.

  But while fixing one variable while altering the other would make any problem more solvable, it’s almost always the resource variable that is presumed to be fixed in India. For example, a common refrain is that ISRO’s allocation is nowhere near that of NASA, so ISRO must figure how best to use its limited funds – and can’t afford luxuries like a full-fledged outreach team.

  There are two problems in the context of resource availability here: 1. an outreach team proper is implied to be the product of a much higher allocation than has been made, i.e. comparable to that of NASA, and 2. incremental increases in allocation are precluded. Neither of these is right, of course: ISRO doesn’t have to wait for NASA’s volume of resources in order to set up an outreach team.

  The deeper issue here is not that ISRO doesn’t have the requisite funds but that it doesn’t feel a better outreach unit is necessary. Here, it pays to acknowledge that ISRO has received not inconsiderable allocations over the years, as well as has enjoyed bipartisan support and (relative) freedom from bureaucratic interference, so it cops much of the blame as well. But in the rest of India, the situation is flipped: many institutions, and their members, have fewer resources than they have ideas and that affects research in a way of its own.

  For example, in the context of grants and fellowships, there’s the obvious illusory ‘prestige constraint’ at the international level – whereby award-winners and self-proclaimed hotshots wield power by presuming prestige to be tied to a few accomplishments, such as winning a Nobel Prize, publishing papers in The Lancet and Nature or maintaining an h-index of 150. These journals and award-giving committees in turn boast of their selectiveness and elitism. (Note: don’t underestimate the influence of these journals.)

  Then there’s the financial constraint for Big Science projects. Some of them may be necessary to keep, say, enthusiastic particle physicists from being carried away. But more broadly, a gross mismatch between the availability of resources and the scale of expectations may ultimately be detrimental to science itself.

  These markers of prestige and power are all essentially instruments of control – and there is no reason this equation should be different in India. Funding for science in India is only resource-constrained to the extent to which the government, which is the principal funder, deems it to be.

  The Indian government’s revised expenditure on ‘scientific departments’ in 2019-2020 was Rs 27,694 crore. The corresponding figure for defence was Rs 3,16,296 crore. If Rs 1,000 crore were moved from the latter to the former, the defence spend would have dropped only by 0.3% but the science spend would have increased by 3.6%. Why, if the money spent on the Statue of Unity had instead been diverted to R&D, the hike would have nearly tripled.

  Effectively, the argument that ‘India’s resources are limited’ is tenable only when resources are constrained on all fronts, or specific fronts as determined by circumstances – and not when it seems to be gaslighting an entire sector. The determination of these circumstances in turn should be completely transparent; keeping them opaque will simply create more ground for arbitrary decisions.

  Of course, in a pragmatic sense, it’s best to use one’s resources wisely – but this position can’t be generalised to the point where optimising for what’s available becomes morally superior to demanding more (even as we must maintain the moral justification of being allowed to ask how much money is being given to whom). That is, constantly making the system work more efficiently is a sensible aspiration, but it shouldn’t come – as it often does at the moment, perhaps most prominently in the case of CSIR – at the cost of more resources. If people are discontented because they don’t have enough, their ire should be directed at the total allocation itself more than how a part of it is being apportioned.

  In a different context, a physicist had pointed out a few years ago that when the US government finally scrapped the proposed Superconducting Supercollider in the early 1990s, the freed-up funds weren’t directed back into other areas of science, as scientists thought they would be. (I couldn’t find the link to this comment nor recall the originator – but I think it was either Sabine Hossenfelder or Sean Carroll; I’ll update this post when I do.) I suspect that if the group of people that had argued thus had known this would happen, it might have argued differently.

  I don’t know if a similar story has played out in India; I certainly don’t know if any Big Science projects have been commissioned and then scrapped. In fact, the opposite has happened more often: whereby projects have done more with less by repurposing an existing resource (examples here, here and here). (Having to fight so hard to realise such mega-projects in India could be motivating those who undertake one to not give up!)

  In the non-Big-Science and more general sense, an efficiency problem raises its head. One variant of this is about research v. teaching: what does India need more of, or what’s a more efficient expense, to achieve scientific progress – institutions where researchers are free to conduct experiments without being saddled with teaching responsibilities or institutions where teaching is just as important as research? This question has often been in the news in India in the last few years, given the erstwhile HRD Ministry’s flip-flops on whether teachers should conduct research. I personally agree that we need to ‘let teachers teach’.

  The other variant is concerned with blue-sky research: when are scientists more productive – when the government allows a “free play of free intellects” or if it railroads them on which problems to tackle? Given the fabled shortage of teachers at many teaching institutions, it’s easy to conclude that a combination of economic and policy decisions have funnelled India’s scholars into neglecting their teaching responsibilities. In turn, rejigging the fraction of teaching or teaching-cum-research versus research-only institutions in India in favour of the former, which are less resource-intensive, could free up some funds.

  But this is also more about pragmatism than anything else – somewhat like untangling a bundle of wires before straightening them out instead of vice versa, or trying to do both at once. As things stand, India’s teaching institutions also need more money. Some reasons there is a shortage of teachers include the fact that they are often not paid well or on time, especially if they are employed at state-funded colleges; the institutions’ teaching facilities are subpar (or non-existent); if jobs are located in remote places and the institutions haven’t had the leeway to consider upgrading recreational facilities; etc.

  Teaching at the higher-education level in India is also harder because of the poor state of government schools, especially outside tier I cities. This brings with it a separate raft of problems, including money.

  Finally, a more ‘local’ example of prestige as well as financial constraints that also illustrates the importance of this PoV is the question of why the Swarnajayanti Fellowships have been awarded to so few women, and how this problem can be ‘fixed’.

  If the query about which men should be excluded to accommodate women sounds like a reasonable question – you’re probably assuming that the number of fellows has to be limited to a certain number, dictated in turn by the amount of money the government has said can be awarded through these fellowships. But if the government allocated more money, we could appreciate all the current laureates as well as many others, and arguably without diluting the ‘quality’ of the competition (given just how many scholars there are).

  Resource constraints obviously can’t explain or resolve everything that stands in the way of more women, trans-people, gender-non-binary and gender-non-conforming scholars receiving scholarships, fellowships, awards and prominent positions within academia. But axiomatically, it’s important to see that ‘fixing’ this problem requires action on two fronts, instead of just one – make academia less sexist and misogynistic and secure more funds. The constraints are certainly part of the problem, particularly when they are wielded as an excuse to concentrate more resources, and more power, in the hands of the already privileged, even as the constraints may not be real themselves.

  In the final analysis, science doesn’t have to be a powerplay, and we don’t have to honour anyone at the expense of another. But deferring to such wisdom could let the fundamental causes of this issue off the hook.

  2020.11.12

• My heart of physics

  Every July 4, I have occasion to remember two things: the discovery of the Higgs boson, and my first published byline for an article about the discovery of the Higgs boson. I have no trouble believing it’s been eight years since we discovered this particle, using the Large Hadron Collider (LHC) and its ATLAS and CMS detectors, in Geneva. I’ve greatly enjoyed writing about particle physics in this time, principally because closely engaging with new research and the scientists who worked on them allowed me to learn more about a subject that high school and college had let me down on: physics.

  In 2020, I haven’t been able to focus much on the physical sciences in my writing, thanks to the pandemic, the lockdown, their combined effects and one other reason. This has been made doubly sad by the fact that the particle physics community at large is at an interesting crossroads.

  In 2012, the LHC fulfilled the principal task it had been built for: finding the Higgs boson. After that, physicists imagined the collider would discover other unknown particles, allowing theorists to expand their theories and answer hitherto unanswered questions. However, the LHC has since done the opposite: it has narrowed the possibilities of finding new particles that physicists had argued should exist according to their theories (specifically supersymmetric partners), forcing them to look harder for mistakes they might’ve made in their calculations. But thus far, physicists have neither found mistakes nor made new findings, leaving them stuck in an unsettling knowledge space from which it seems there might be no escape (okay, this is sensationalised, but it’s also kinda true).

  Right now, the world’s particle physicists are mulling building a collider larger and more powerful than the LHC, at a cost of billions of dollars, in the hopes that it will find the particles they’re looking for. Not all physicists are agreed, of course. If you’re interested in reading more, I’d recommend articles by Sabine Hossenfelder and Nirmalya Kajuri and spiralling out from there. But notwithstanding the opposition, CERN – which coordinates the LHC’s operations with tens of thousands of personnel from scores of countries – recently updated its strategy vision to recommend the construction of such a machine, with the ability to produce copious amounts of Higgs bosons in collisions between electrons and positrons (a.k.a. ‘Higgs factories’). China has also announced plans of its own build something similar.

  Meanwhile, scientists and engineers are busy upgrading the LHC itself to a ‘high luminosity version’, where luminosity represents the number of interesting events the machine can detect during collisions for further study. This version will operate until 2038. That isn’t a long way away because it took more than a decade to build the LHC; it will definitely take longer to plan for, convince lawmakers, secure the funds for and build something bigger and more complicated.

  There have been some other developments connected to the current occasion in terms of indicating other ways to discover ‘new physics’, which is the collective name for phenomena that will violate our existing theories’ predictions and show us where we’ve gone wrong in our calculations.

  The most recent one I think was the ‘XENON excess’, which refers to a moderately strong signal recorded by the XENON 1T detector in Italy that physicists think could be evidence of a class of particles called axions. I say ‘moderately strong’ because the statistical significance of the signal’s strength is just barely above the threshold used to denote evidence and not anywhere near the threshold that denotes a discovery proper.

  It’s evoked a fair bit of excitement because axions count as new physics – but when I asked two physicists (one after the other) to write an article explaining this development, they refused on similar grounds: that the significance makes it seem likely that the signal will be accounted for by some other well-known event. I was disappointed of course but I wasn’t surprised either: in the last eight years, I can count at least four instances in which a seemingly inexplicable particle physics related development turned out to be a dud.

  The most prominent one was the ‘750 GeV excess’ at the LHC in December 2015, which seemed to be a sign of a new particle about six-times heavier than a Higgs boson and 800-times heavier than a proton (at rest). But when physicists analysed more data, the signal vanished – a.k.a. it wasn’t there in the first place and what physicists had seen was likely a statistical fluke of some sort. Another popular anomaly that went the same way was the one at Atomki.

  But while all of this is so very interesting, today – July 4 – also seems like a good time to admit I don’t feel as invested in the future of particle physics anymore (the ‘other reason’). Some might say, and have said, that I’m abandoning ship just as the field’s central animus is moving away from the physics and more towards sociology and politics, and some might be right. I get enough of the latter subjects when I work on the non-physics topics that interest me, like research misconduct and science policy. My heart of physics itself is currently tending towards quantum mechanics and thermodynamics (although not quantum thermodynamics).

  One peer had also recommended in between that I familiarise myself with quantum computing while another had suggested climate-change-related mitigation technologies, which only makes me wonder now if I’m delving into those branches of physics that promise to take me farther away from what I’m supposed to do. And truth be told, I’m perfectly okay with that. 🙂 This does speak to my privileges – modest as they are on this particular count – but when it feels like there’s less stuff to be happy about in the world with every new day, it’s time to adopt a new hedonism and find joy where it lies.

  2020.07.04