With all the hype around machine learning, I occasionally get asked if it could be used to make predictions for particle colliders, like the LHC.
Physicists do use machine learning these days, to be clear. There are tricks and heuristics, ways to quickly classify different particle collisions and speed up computation. But if you’re imagining something that replaces particle physics calculations entirely, or even replace the LHC itself, then you’re misunderstanding what particle physics calculations are for.
Why do physicists try to predict the results of particle collisions? Why not just observe what happens?
Physicists make predictions not in order to know what will happen in advance, but to compare those predictions to experimental results. If the predictions match the experiments, that supports existing theories like the Standard Model. If they don’t, then a new theory might be needed.
Those predictions certainly don’t need to be made by humans: most of the calculations are done by computers anyway. And they don’t need to be perfectly accurate: in particle physics, every calculation is an approximation. But the approximations used in particle physics are controlled approximations. Physicists keep track of what assumptions they make, and how they might go wrong. That’s not something you can typically do in machine learning, where you might train a neural network with millions of parameters. The whole point is to be able to check experiments against a known theory, and we can’t do that if we don’t know whether our calculation actually respects the theory.
That difference, between caring about the result and caring about how you got there, is a useful guide. If you want to predict how a protein folds in order to understand what it does in a cell, then you will find AlphaFold useful. If you want to confirm your theory of how protein folding happens, it will be less useful.
Some industries just want the final result, and can benefit from machine learning. If you want to know what your customers will buy, or which suppliers are cheating you, or whether your warehouse is moldy, then machine learning can be really helpful.
Other industries are trying, like particle physicists, to confirm that a theory is true. If you’re running a clinical trial, you want to be crystal clear about how the trial data turn into statistics. You, and the regulators, care about how you got there, not just about what answer you got. The same can be true for banks: if laws tell you you aren’t allowed to discriminate against certain kinds of customers for loans, you need to use a method where you know what traits you’re actually discriminating against.
So will physicists use machine learning? Yes, and more of it over time. But will they use it to replace normal calculations, or replace the LHC? No, that would be missing the point.
I posted a link last week to a dialogue written by a former colleague of mine, Sylvain Ribault. Sylvain’s dialogue is a summary of different perspectives on academic publishing. Unlike certain more famous dialogues written by physicists, Sylvain’s account doesn’t have a clear bias: he’s trying to set out the concerns different stakeholders might have and highlight the history of the subject, without endorsing one particular approach as the right one.
The purpose of such a dialogue is to provoke thought, and true to its purpose, the dialogue got me thinking.
Why do peer review? Why do we ask three or so people to read every paper, comment on it, and decide whether it should be published? While one can list many reasons, they seem to fall into two broad groups:
We want to distinguish better science from worse science. We want to reward the better scientists with jobs and grants and tenure. To measure whether scientists are better, we want to see whether they publish more often in the better journals. We then apply those measures on up the chain, funding universities more when they have better scientists, and supporting grant programs that bring about better science.
We want published science to be true. We want to make sure that when a paper is published that the result is actually genuine, free both from deception and from mistakes. We want journalists and the public to know which scientific results are valid, and we want scientists to know what results they can base their own research on.
The first set of goals is a product of scarcity. If we could pay every scientist and fund every scientific project with no cost, we wouldn’t need to worry so much about better and worse science. We’d fund it all and see what happens. The second set of goals is more universal: the whole point of science is to find out the truth, and we want a process that helps to achieve that.
My approach to science is to break problems down. What happens if we had only the second set of concerns, and not the first?
Well, what happens to hobbyists?
I’ve called hobby communities a kind of “post-scarcity academia”. Hobbyists aren’t trying to get jobs doing their hobby or get grants to fund it. They have their day jobs, and research their hobby as a pure passion project. There isn’t much need to rank which hobbyists are “better” than others, but they typically do care about whether what they write is true. So what happens when it’s not?
Sometimes, not much.
My main hobby community was Dungeons and Dragons. In a game with over 50 optional rulebooks covering multiple partially compatible-editions, there were frequent arguments about what the rules actually meant. Some were truly matters of opinion, but some were true misunderstandings, situations where many people thought a rule worked a certain way until they heard the right explanation.
One such rule regarded a certain type of creature called a Warbeast. Warbeasts, like Tolkien’s Oliphaunts, are “upgraded” versions of more normal wild animals, bred and trained for war. There were rules to train a Warbeast, and people interpreted these rules differently: some thought you could find an animal in the wild and train it to become a Warbeast, others thought the rules were for training a creature that was already a Warbeast to fight.
I supported the second interpretation: you can train an existing Warbeast, you can’t train a wild animal to make it into a Warbeast. As such, keep in mind, I’m biased. But every time I explained the reasoning (pointing out that the text was written in the context of an earlier version of the game, and how the numbers in it matched up with that version), people usually agreed with me. And yet, I kept seeing people use the other interpretation. New players would come in asking how to play the game, and get advised to go train wild animals to make them into Warbeasts.
Ok, so suppose the Dungeons and Dragons community had a peer review process. Would that change anything?
Not really! The wrong interpretation was popular. If whoever first proposed it got three random referees, there’s a decent chance none of them would spot the problem. In good science, sometimes the problems with an idea are quite subtle. Referees will spot obvious issues (and not even all of those!), but only the most diligent review (which sometimes happens in mathematics, and pretty much nowhere else) can spot subtle flaws in an argument. For an experiment, you sometimes need more than that: not just a review, but an actual replication.
What would have helped the Dungeons and Dragons community? Not peer review, but citations.
Suppose that, every time someone suggested you could train a wild animal to make it a Warbeast, they had to link to the first post suggesting you could do this. Then I could go to that first post, and try to convince the author that my interpretation was correct. If I succeeded, the author could correct their post, and then every time someone followed one of these citation links it would tell them the claim was wrong.
Academic citations don’t quite work like this. But the idea is out there. People have suggested letting anyone who wants to review a paper, and publishing the reviews next to the piece like comments on a blog post. Sylvain’s dialogue mentions a setup like this, and some of the risks involved.
Still, a setup like that would have gone a long way towards solving the problem for the Dungeons and Dragons community. It has me thinking that something like that is worth exploring.
When investors put money in a company, they have some control over what that company does. They vote to decide a board, and the board votes to hire a CEO. If the company isn’t doing what the investors want, the board can fire the CEO, or the investors can vote in a new board. Everybody is incentivized to do what the people who gave the money want to happen. And usually, those people want the company to increase its profits, since most of them people are companies with their own investors).
Academics are paid by universities and research centers, funded in the aggregate by governments and student tuition and endowments from donors. But individually, they’re also often funded by grants.
What grant-givers want is more ambiguous. The money comes in big lumps from governments and private foundations, which generally want something vague like “scientific progress”. The actual decision of who gets the money are made by committees made up of senior scientists. These people aren’t experts in every topic, so they have to extrapolate, much as investors have to guess whether a new company will be profitable based on past experience. At their best, they use their deep familiarity with scientific research to judge which projects are most likely to work, and which have the most interesting payoffs. At their weakest, though, they stick with ideas they’ve heard of, things they know work because they’ve seen them work before. That, in a nutshell, is why mainstream research prevails: not because the mainstream wants to suppress alternatives, but because sometimes the only way to guess if something will work is raw familiarity.
(What “works” means is another question. The cynical answers are “publishes papers” or “gets citations”, but that’s a bit unfair: in Europe and the US, most funders know that these numbers don’t tell the whole story. The trivial answer is “achieves what you said it would”, but that can’t be the whole story, because some goals are more pointless than others. You might want the answer to be “benefits humanity”, but that’s almost impossible to judge. So in the end the answer is “sounds like good science”, which is vulnerable to all the fads you can imagine…but is pretty much our only option, regardless.)
So are academics incentivized to do what the grant committees want? Sort of.
Science never goes according to plan. Grant committees are made up of scientists, so they know that. So while many grants have a review process afterwards to see whether you achieved what you planned, they aren’t all that picky about it. If you can tell a good story, you can explain why you moved away from your original proposal. You can say the original idea inspired a new direction, or that it became clear that a new approach was necessary. I’ve done this with an EU grant, and they were fine with it.
Looking at this, you might imagine that an academic who’s a half-capable storyteller could get away with anything they wanted. Propose a fashionable project, work on what you actually care about, and tell a good story afterwards to avoid getting in trouble. As long as you’re not literally embezzling the money (the guy who was paying himself rent out of his visitor funding, for instance), what could go wrong? You get the money without the incentives, you move the scientific world and nobody gets to move you.
I can’t speak for Hossenfelder, but I’ve also put some thought into how to choose what to research, about whether I could actually be an unmoved mover. A few things get in the way:
First, applying for grants doesn’t just take storytelling skills, it takes scientific knowledge. Grant committees aren’t experts in everything, but they usually send grants to be reviewed by much more appropriate experts. These experts will check if your grant makes sense. In order to make the grant make sense, you have to know enough about the faddish topic to propose something reasonable. You have to keep up with the fad. You have to spend time reading papers, and talking to people in the faddish subfield. This takes work, but also changes your motivation. If you spend time around people excited by an idea, you’ll either get excited too, or be too drained by the dissonance to get any work done.
Second, you can’t change things that much. You still need a plausible story as to how you got from where you are to where you are going.
Third, you need to be a plausible person to do the work. If the committee looks at your CV and sees that you’ve never actually worked on the faddish topic, they’re more likely to give a grant to someone who’s actually worked on it.
Fourth, you have to choose what to do when you hire people. If you never hire any postdocs or students working on the faddish topic, then it will be very obvious that you aren’t trying to research it. If you do hire them, then you’ll be surrounded by people who actually care about the fad, and want your help to understand how to work with it.
Ultimately, to avoid the grant committee’s incentives, you need a golden tongue and a heart of stone, and even then you’ll need to spend some time working on something you think is pointless.
Even if you don’t apply for grants, even if you have a real permanent position or even tenure, you still feel some of these pressures. You’re still surrounded by people who care about particular things, by students and postdocs who need grants and jobs and fellow professors who are confident the mainstream is the right path forward. It takes a lot of strength, and sometimes cruelty, to avoid bowing to that.
So despite the ambiguous rules and lack of oversight, academics still respond to incentives: they can’t just do whatever they feel like. They aren’t bound by shareholders, they aren’t expected to make a profit. But ultimately, the things that do constrain them, expertise and cognitive load, social pressure and compassion for those they mentor, those can be even stronger.
I suspect that those pressures dominate the private sector as well. My guess is that for all that companies think of themselves as trying to maximize profits, the all-too-human motivations we share are more powerful than any corporate governance structure or org chart. But I don’t know yet. Likely, I’ll find out soon.
Peter Higgs, the theoretical physicist whose name graces the Higgs boson, died this week.
Peter Higgs, after the Higgs boson discovery was confirmed
This post isn’t an obituary: you can find plenty of those online, and I don’t have anything special to say that others haven’t. Reading the obituaries, you’ll notice they summarize Higgs’s contribution in different ways. Higgs was one of the people who proposed what today is known as the Higgs mechanism, the principle by which most (perhaps all) elementary particles gain their mass. He wasn’t the only one: Robert Brout and François Englert proposed essentially the same idea in a paper that was published two months earlier, in August 1964. Two other teams came up with the idea slightly later than that: Gerald Guralnik, Carl Richard Hagen, and Tom Kibble were published one month after Higgs, while Alexander Migdal and Alexander Polyakov found the idea independently in 1965 but couldn’t get it published till 1966.
Higgs did, however, do something that Brout and Englert didn’t. His paper doesn’t just propose a mechanism, involving a field which gives particles mass. It also proposes a particle one could discover as a result. Read the more detailed obituaries, and you’ll discover that this particle was not in the original paper: Higgs’s paper was rejected at first, and he added the discussion of the particle to make it more interesting.
At this point, I bet some of you are wondering what the big deal was. You’ve heard me say that particles are ripples in quantum fields. So shouldn’t we expect every field to have a particle?
Tell that to the other three Higgs bosons.
Electromagnetism has one type of charge, with two signs: plus, and minus. There are electrons, with negative charge, and their anti-particles, positrons, with positive charge.
Quarks have three types of charge, called colors: red, green, and blue. Each of these also has two “signs”: red and anti-red, green and anti-green, and blue and anti-blue. So for each type of quark (like an up quark), there are six different versions: red, green, and blue, and anti-quarks with anti-red, anti-green, and anti-blue.
Diagram of the colors of quarks
When we talk about quarks, we say that the force under which they are charged, the strong nuclear force, is an “SU(3)” force. The “S” and “U” there are shorthand for mathematical properties that are a bit too complicated to explain here, but the “(3)” is quite simple: it means there are three colors.
The Higgs boson’s primary role is to make the weak nuclear force weak, by making the particles that carry it from place to place massive. (That way, it takes too much energy for them to go anywhere, a feeling I think we can all relate to.) The weak nuclear force is an “SU(2)” force. So there should be two “colors” of particles that interact with the weak nuclear force…which includes Higgs bosons. For each, there should also be an anti-color, just like the quarks had anti-red, anti-green, and anti-blue. So we need two “colors” of Higgs bosons, and two “anti-colors”, for a total of four!
But the Higgs boson discovered at the LHC was a neutral particle. It didn’t have any electric charge, or any color. There was only one, not four. So what happened to the other three Higgs bosons?
The real answer is subtle, one of those physics things that’s tricky to concisely explain. But a partial answer is that they’re indistinguishable from the W and Z bosons.
Normally, the fundamental forces have transverse waves, with two polarizations. Light can wiggle along its path back and forth, or up and down, but it can’t wiggle forward and backward. A fundamental force with massive particles is different, because they can have longitudinal waves: they have an extra direction in which they can wiggle. There are two W bosons (plus and minus) and one Z boson, and they all get one more polarization when they become massive due to the Higgs.
That’s three new ways the W and Z bosons can wiggle. That’s the same number as the number of Higgs bosons that went away, and that’s no coincidence. We physicist like to say that the W and Z bosons “ate” the extra Higgs, which is evocative but may sound mysterious. Instead, you can think of it as the two wiggles being secretly the same, mixing together in a way that makes them impossible to tell apart.
The “count”, of how many wiggles exist, stays the same. You start with four Higgs wiggles, and two wiggles each for the precursors of the W+, W-, and Z bosons, giving ten. You end up with one Higgs wiggle, and three wiggles each for the W+, W-, and Z bosons, which still adds up to ten. But which fields match with which wiggles, and thus which particles we can detect, changes. It takes some thought to look at the whole system and figure out, for each field, what kind of particle you might find.
Higgs did that work. And now, we call it the Higgs boson.
They say when all you have is a hammer, everything looks like a nail.
Academics are a bit smarter than that. Confidently predict a world of nails, and you fall to the first paper that shows evidence of a screw. There are limits to how long you can delude yourself when your job is supposed to be all about finding the truth.
You can make your own nails, though.
Suppose there’s something you’re really good at. Maybe, like many of my past colleagues, you can do particle physics calculations faster than anyone else, even when the particles are super-complicated hypothetical gravitons. Maybe you know more than anyone else about how to make a quantum computer, or maybe you just know how to build a “quantum computer“. Maybe you’re an expert in esoteric mathematics, who can re-phrase anything in terms of the arcane language of category theory.
That’s your hammer. Get good enough with it, and anyone with a nail-based problem will come to you to solve it. If nails are trendy, then you’ll impress grant committees and hiring committees, and your students will too.
When nails aren’t trendy, though, you need to try something else. If your job is secure, and you don’t have students with their own insecure jobs banging down your door, then you could spend a while retraining. You could form a reading group, pick up a textbook or two about screwdrivers and wrenches, and learn how to use different tools. Eventually, you might find a screwdriving task you have an advantage with, something you can once again do better than everyone else, and you’ll start getting all those rewards again.
Or, maybe you won’t. You’ll get less funding to hire people, so you’ll do less research, so your work will get less impressive and you’ll get less funding, and so on and so forth.
Instead of risking that, most academics take another path. They take what they’re good at, and invent new problems in the new trendy area to use that expertise.
If everyone is excited about gravitational waves, you turn a black hole calculation into a graviton calculation. If companies are investing in computation in the here-and-now, then you find ways those companies can use insights from your quantum research. If everyone wants to know how AI works, you build a mathematical picture that sort of looks like one part of how AI works, and do category theory to it.
At first, you won’t be competitive. Your hammer isn’t going to work nearly as well as the screwdrivers people have been using forever for these problems, and there will be all sorts of new issues you have to solve just to get your hammer in position in the first place. But that doesn’t matter so much, as long as you’re honest. Academic research is expected to take time, applications aren’t supposed to be obvious. Grant committees care about what you’re trying to do, as long as you have a reasonably plausible story about how you’ll get there.
(Investors are also not immune to a nice story. Customers are also not immune to a nice story. You can take this farther than you might think.)
So, unlike the re-trainers, you survive. And some of the time, you make it work. Your hammer-based screwdriving ends up morphing into something that, some of the time, actually does something the screwdrivers can’t. Instead of delusionally imagining nails, you’ve added a real ersatz nail to the world, where previously there was just a screw.
Making nails is a better path for you. Is it a better path for the world? I’m not sure.
If all those grants you won, all those jobs you and your students got, all that money from investors or customers drawn in by a good story, if that all went to the people who had the screwdrivers in the first place, could they have done a better job?
Sometimes, no. Sometimes you happen upon some real irreproducible magic. Your hammer is Thor’s hammer, and when hefted by the worthy it can do great things.
Sometimes, though, your hammer was just the hammer that got the funding. Now every screwdriver kit has to have a space for a little hammer, when it could have had another specialized screwdriver that fit better in the box.
In the end, the world is build out of these kinds of ill-fitting toolkits. We all try to survive, both as human beings and by our sub-culture’s concept of the good life. We each have our hammers, and regardless of whether the world is full of screws, we have to convince people they want a hammer anyway. Everything we do is built on a vast rickety pile of consequences, the end-results of billions of people desperate to be wanted. For those of us who love clean solutions and ideal paths, this is maddening and frustrating and terrifying. But it’s life, and in a world where we never know the ideal path, screw-nails and nail-screws are the best way we’ve found to get things done.
In last week’s announcement, I mentioned I’d have a few follow-up posts. This week is a guest post. I want to let my wife tell her side of the story, to talk publicly about what she’s experienced over the last six months.
If you are a frequent reader of this blog, you probably know that 4gravitons relocated last year to France, following a long-coveted permanent academic position at the Institute for Theoretical Physics (IPhT) of CEA Paris-Saclay. Along with 4gravitons, I also moved to France as a trailing spouse. This is not an unusual situation, academic spouses agreeing to leave behind their friends and career to allow the academic in the relationship to develop their career. I had even set some conditions that I thought were necessary for me to successfully integrate elsewhere (access to employment, an intelligible healthcare system, good public transit), a list of desirable traits (in or near a medium-to-large city, prior knowledge of the language, walkable neighborhood), and some places I was unwilling to move to. When the offer for a position in France arrived, we thought it was almost ideal:
France is an EU country, which would give me direct access to employment (by the EU directive on Freedom of Movement),
France is also somewhat renowned for having a sensible working healthcare system, even though in recent times it has been stretched thin,
IPhT is less than an hour away from Paris, and
Both 4gravitons and I already had a B1/B2 level in French (you can find the CEFR level descriptors here).
However, we have decided to leave France only 6 months after arriving. What happened?
I wanted to put one of Escher’s labyrinths here, but they’re still under copyright.
The quest for a Carte de Séjour (and access to the labor market)
As I wrote earlier, being able to work was a necessary condition for me to relocate. I work in education, which often requires a good deal of paperwork (since countries correctly want to make sure their young people are in a safe, nurturing environment). I had heard that France was facing a shortage of teachers, so I was hopeful about my prospects. I applied for one position which seemed like a perfect fit and got through a couple of interviews before the legal right to work issues started. EU law states that EU spouses have access to employment in EU countries on arrival (they should get the same rights as their European partners); however, in France employers are liable if they hire someone illegally so they are extremely cautious when hiring foreigners. In practice, this means employers will NOT hire EU spouses if they do not have a document from the French authorities explicitly stating their right to work. Since it is not possible to start the process to get such a document before arriving in France, finding work would have to wait.
One day after arriving in France, still hoping things would go smoothly and we could build a good life there, I collected all the document required by EU law to apply for a Carte de Séjour (residence card), went to the neighborhood Photomaton to have compliant photos taken, and uploaded the documents and photo-ID to the website of ANEF, the agency that handles the digital side of French immigration. EU law grants EU spouses 3 months to apply for the Carte de Séjour, but I wanted to have the process started as soon as possible so I could work. Naïvely, I thought I would be issued a document stating that I had applied for a Carte de Séjour under EU law and thus was allowed employment, the way it works in other EU countries. This was not the case. I was, instead, given a letter saying that I had applied for a Carte de Séjour, and that the document did not grant access to either employment or social benefits (such as healthcare, more on this below). To make matters worse, our sous-préfécture (the part of local government that handles the application) listed average waiting times for first demands at 161 days.
Well, at least the process was started and, in my head, the long wait times would likely only apply to complicated cases. I was arriving as an EU spouse, after having lived in another EU country (since 4gravitons had been working at the Niels Bohr Institute, in Denmark) for quite some time. It would likely be a short wait. It was just a matter of waiting for an e-mail when the process actually started and making sure to submit further documentation quickly, if it was deemed necessary.
A couple of months later, the email had not yet arrived (and work opportunities kept vanishing due to lack of papers), so we started asking for confirmation that my documents had indeed been received by our local sous-préfécture. We wrote to ANEF (“due to a technical error, we cannot answer your question”), called the sous-préfécture (“nobody here can answer your question”), support organizations (“You have the wrong visa! Can you go to another country and apply for a long-term visa from there?”), and so on. This went on for a long time despite local contacts reaching out to our sous-préfécture, our préfect, and other connections to try and accelerate the process. I finally received the e-mail starting the process (requesting some more documents, as well as some I had already sent) about 5 months after submitting the application (it took exactly 148 days, I counted). At this point, I was also granted a new letter attesting that I was legally in France (my short-term Schengen visa having expired much earlier) and that explicitly did not grant access to either employment (without a work authorization) or social benefits.
Healthcare for the undocumented
To make things even more complicated, I started having unusual symptoms a few weeks after our move to France. In the worst instance, the symptoms were worrying enough that an ambulance was sent to take me to the emergency room for an MRI (luckily, it was not serious). Note that I did not have a health card, so the ambulance had to be paid in cash before they would move me, the hospital sent a bill for the MRI by mail some weeks later, and the government sent a bill for the emergency care four months later. Luckily, we bought private insurance before moving, since we have relocated before and know that sometimes it takes a little time before one is signed up with the local healthcare institutions. Unluckily, hospitals here will not deal with insurance companies directly so we had to pay and file for reimbursement (this involves papers called feuille de soins, and the ambulance did not give us one, so no reimbursement for that). The following 3 or 4 months involved many specialist visits, lots of labs, lots of feuilles de soins… and very limited improvement on my symptoms. Since we could not have a family doctor (this requires a health card and an infinite amount of patience given that most general doctors have no space for new patients), appointments often consisted of the same questions, more referrals, confusion over a patient arriving with a giant file of previous documents, and no answers. At the end, the only answer proposed was that it may all be a physical expression of stress and anxiety.
The aforementioned situation was adding significant complications to our lives so, France being a country with socialized medicine, we started the process required to register me for a Carte Vitale (this is the name of the French health card). Residents in France aren’t automatically covered, but they are either registered for coverage by their employer or register themselves as dependents of someone with coverage. We reached out to CPAM (the French agency that controls socialized health insurance) and were given the forms to apply for coverage and a list of documents, which included a valid residency document (long-term visa or Carte de Séjour). EU spouses are not required to get a long-term visa (the French embassy explicitly told us I should get a short-term visa, and only because our residency cards for Denmark were expiring around the time of relocation) and the Carte de Séjour process was still ongoing, so we had a problem. Regardless, we made a file, and included our marriage certificate, the letter stating I had applied for a residence card, and proof of residency and work in France for 4gravitons, which shows the legality of my residence in France under EU regulations. The instructions are to send the file by mail to the corresponding CPAM office, which we tried to do but the postal office lost the letter. We eventually got an appointment to hand the documents in person and were told directly that I had the wrong visa and my request would likely be denied due to the lack of Carte de Séjour. We repeated the rules established by the EU (lack of a Carte de Séjour CANNOT be used to justify the denial of rights to EU families) and gave them the dossier. A month or so later, a letter came in the mail stating that my request had been denied because I had not been a resident for three months (at that point, I had been a resident for 2 and a half months so that was not much of an issue); a few weeks later, once my three-month visa had expired, a different letter arrived changing the reason for refusal to the lack of legal resident status.
Everyone ♥️ Paris, France
As you may well imagine, I was not feeling much appreciation for the City of Lights given our difficulties settling in and the isolation imposed by my status (legal resident but undocumented). Yet, whenever I have tried to explain why I was anxious, frustrated, or depressed, I encountered very little empathy or understanding. It often felt as if, by describing my experiences in the city, I was criticizing a core belief for people: that Paris is a magical place where one eats wonderful food and strolls about beautiful places.
In sensing my unhappiness in (or near) Paris, I was often advised to go spend more time in the museums (the ones I am most interested in are quite expensive and permanently crowded) or walking around the nice areas of Paris (but beware not to take a wrong turn, for it is easy to find oneself in a less-than-nice place). This continued even if I explained that I have been to Paris, have seen the beautiful museums and manicured parks, and I never much enjoyed it.
I moved here knowing that Paris was not a city I loved, but expecting it would provide access to entertainment (art, theater, gaming, etc) and to a variety of other resources (like materials for artwork or ingredients for my traditional foods). I was quite unhappy when the reliability of the RER-B became a problem: we ended up defaulting to scheduling almost two hours for any Paris trip to ensure we would arrive on time. Despite the extended time, there were occasions when we almost missed a meeting time due to train delays and cancellations. In the end, access to all the nice things in Paris was limited by logistics.
An unintegrated immigrant
Until this move, I thought that integration into developed countries was mostly a matter of individual effort: learn the language, find employment and connections to the local community, and understand that things are different than in your previous home. I can no longer hold this belief. I tried, as much as I could, to interact with our local community. I took any opportunity to speak French, and often was made to feel dumb for not finding the right terms; an ophthalmologist once welcomed me by saying “Oh, you’re the patient who does not speak French” in French (try describing different kinds of eye pain in a foreign language). I signed-up for more French lessons which seemed to focus more on local slang than on useful words (my vocabulary needs more help than my grammar for French). I also joined some art lessons and a local vocal ensemble, where I met some lovely people but had little chance of creating more in-depth connections.
Finally, after months of trying and failing to integrate, Newtonmas came. The few friends we had here all left to visit their families. I still had no papers and could not leave France. On top of this, there was an unexpected death in my family in the lead-up to the holidays. I found myself, almost 5 months after arriving, unemployed (and with no access to the job market), uninsured (and paying for healthcare and a lot of counseling out of pocket), undocumented (at this point, with no valid visa and no way to prove I was in France legally), and grieving alone in a foreign country. We knew that I could not stay here. And thus, we cannot stay here.
Integration requires effort from the immigrant, but it also requires effort from the country. It requires a country willing to give basic access to the requirements of life, to let immigrants step into the public sphere under fair conditions, and to do so consistently and reliably. France, in its current state, cannot do this. I hope it can improve, but I am not required to wait here for it. We’ll be elsewhere, integrating into another country and contributing to their community instead.
A while back I wrote a post trying to reassure you that the Large Hadron Collider cannot create a black hole that could destroy the Earth. If you’re the kind of person who is worried about this kind of thing, you’ve probably heard a variety of arguments: that it hasn’t happened yet, despite the LHC running for quite some time, that it didn’t happen before the LHC with cosmic rays of comparable energy, and that a black hole that small would quickly decay due to Hawking radiation. I thought it would be nice to give a different sort of argument, a back-of-the-envelope calculation you can try out yourself, showing that even if a black hole was produced using all of the LHC’s energy and fell directly into the center of the Earth, and even if Hawking radiation didn’t exist, it would still take longer than the lifetime of the universe to cause any detectable damage. Modeling the black hole as falling through the Earth and just slurping up everything that falls into its event horizon, it wouldn’t even double in size before the stars burn out.
Before the LHC even turned on, the experts were hard at work studying precisely this question. The paper has two authors, Steve Giddings and Michelangelo Mangano. Giddings is an expert on the problem of quantum gravity, while Mangano is an expert on LHC physics, so the two are exactly the dream team you’d ask for to answer this question. Like me, they pretend that black holes don’t decay due to Hawking radiation, and pretend that one falls to straight from the LHC to the center of the Earth, for the most pessimistic possible scenario.
Unlike me, but like my friend, they point out that the Earth is not actually a uniform sphere of matter. It’s made up of particles: quarks arranged into nucleons arranged into nuclei arranged into atoms. And a black hole that hits a nucleus will probably not just slurp up an event horizon-sized chunk of the nucleus: it will slurp up the whole nucleus.
This in turn means that the black hole starts out growing much more fast. Eventually, it slows down again: once it’s bigger than an atom, it starts gobbling up atoms a few at a time until eventually it is back to slurping up a cylinder of the Earth’s material as it passes through.
But an atom-sized black hole will grow faster than an LHC-energy-sized black hole. How much faster is estimated in the Giddings and Mangano paper, and it depends on the number of dimensions. For eight dimensions, we’re safe. For fewer, they need new arguments.
Wait a minute, you might ask, aren’t there only four dimensions? Is this some string theory nonsense?
Kind of, yes. In order for the LHC to produce black holes, gravity would need to have a much stronger effect than we expect on subatomic particles. That requires something weird, and the most plausible such weirdness people considered at the time were extra dimensions. With extra dimensions of the right size, the LHC might have produced black holes. It’s that kind of scenario that Giddings and Mangano are checking: they don’t know of a plausible way for black holes to be produced at the LHC if there are just four dimensions.
For fewer than eight dimensions, though, they have a problem: the back-of-the-envelope calculation suggests black holes could actually grow fast enough to cause real damage. Here, they fall back on the other type of argument: if this could happen, would it have happened already? They argue that, if the LHC could produce black holes in this way, then cosmic rays could produce black holes when they hit super-dense astronomical objects, such as white dwarfs and neutron stars. Those black holes would eat up the white dwarfs and neutron stars, in the same way one might be worried they could eat up the Earth. But we can observe that white dwarfs and neutron stars do in fact exist, and typically live much longer than they would if they were constantly being eaten by miniature black holes. So we can conclude that any black holes like this don’t exist, and we’re safe.
If you’ve got a smattering of physics knowledge, I encourage you to read through the paper. They consider a lot of different scenarios, much more than I can summarize in a post. I don’t know if you’ll find it reassuring, since they may not cover whatever you happen to be worried about. But it’s a lot of fun seeing how the experts handle the problem.
Could we do this kind of thing for Newtonmas? A Newtonmas Pageant?
The miraculous child
Historians do know a bit about Newton’s birth. His father (also named Isaac Newton) died two months before he was born. Newton was born prematurely, his mother apparently claimed he could fit inside a quart mug.
The mug may be surprising (it comes in quarts?), but there isn’t really enough material for a proper story here. That said, it would be kind of beside the point if there were. If we’re celebrating science, maybe the story of one particular child is not the story we should be telling.
Instead, we can tell stories about scientific ideas. These often have quite dramatic stories. Instead of running from inn to inn looking for rooms, scientists run from journal to journal trying to publish. Instead of frankincense, myrrh, and gold, there are Nobel prizes. Instead of devils tempting the shepherds away, you have tempting but unproductive ideas. For example, Newton battled ideas from Descartes and Liebniz that suggested gravity could be caused by a vortex of fluid. The idea was popular because it was mechanical-sounding: no invisible force of gravity needed. But it didn’t work, and Newton spent half of the Principia where he wrote down his new science building a theory of fluids so he could say it didn’t work.
So for this Newtonmas, tell the story of a scientific idea: one that had a difficult birth but that, eventually brought pilgrims and gifts from miles around.
Sabine Hossenfelder has gradually transitioned from critical written content about physics to YouTube videos, mostly short science news clips with the occasional longer piece. Luckily for us in the unable-to-listen-to-podcasts demographic, the transcripts of these videos are occasionally published on her organization’s Substack.
Unluckily, it feels like the short news format is leading to some lazy metaphors. There are stories science journalists sometimes tell because they’re easy and familiar, even if they don’t really make sense. Scientists often tell them too, for the same reason. But the more careful voices avoid them.
The “nothing” in the title is the oft-mythologized quantum vacuum. The story goes that in quantum theory, empty space isn’t really empty. It’s full of “virtual” particles, that pop in and out of existence, jostling things around.
(That post I link above, by the way, was partially inspired by a more careful post by Hossenfelder. She does know this stuff. She just doesn’t always use it.)
Let me tell the story Hossenfelder’s piece is telling, in a less silly way:
In the earliest physics classes, you learn that light does not affect other light. Shine two flashlight beams across each other, and they’ll pass right through. You can trace the rays of each source, independently, keeping track of how they travel and bounce around the room.
In quantum theory, that’s not quite true. Light can interact with light, through subtle quantum effects. This effect is tiny, so tiny it hasn’t been measured before. But with ingenious tricks involving tuning three different lasers in exactly the right way, a team of physicists in Dresden has figured out how it could be done.
And see, that’s already cool, right? It’s cool when people figure out how to see things that have never been seen before, full stop.
But the way Hossenfelder presents it, the cool thing about this is that they are “measuring nothing”. That they’re measuring “the quantum vacuum”, really precisely.
And I mean, you can say that, I guess. But it’s equally true of every subtle quantum effect.
In classical physics, electrons should have a very specific behavior in a magnetic field, called their magnetic moment. Quantum theory changes this: electrons have a slightly different magnetic moment, an anomalous magnetic moment. And people have measured this subtle effect: it’s famously the most precisely confirmed prediction in all of science.
That effect can equally well be described as an effect of the quantum vacuum. You can draw the same pictures, if you really want to, with virtual particles popping in and out of the vacuum. One effect (light bouncing off light) doesn’t exist at all in classical physics, while the other (electrons moving in a magnetic field) exists, but is subtly different. But both, in exactly the same sense, are “measurements of nothing”.
So if you really want to stick on the idea that, whenever you measure any subtle quantum effect, you measure “the quantum vacuum”…then we’re already doing that, all the time. Using it to popularize some stuff (say, this experiment) and not other stuff (the LHC is also measuring the quantum vacuum) is just inconsistent.
Better, in my view, to skip the silly talk about nothing. Talk about what we actually measure. It’s cool enough that way.
A while back, someone asked me what my subfield, amplitudeology, is really about. I wrote an answer to that here, a short-term and long-term perspective that line up with the stories we often tell about the field. I talked about how we try to figure out ways to calculate probabilities faster, first for understanding the output of particle colliders like the LHC, then more recently for gravitational wave telescopes. I talked about how the philosophy we use for that carries us farther, how focusing on the minimal information we need to make a prediction gives us hope that we can generalize and even propose totally new theories.
The world doesn’t follow stories, though, not quite so neatly. Try to define something as simple as the word “game” and you run into trouble. Some games have a winner and a loser, some games everyone is on one team, and some games don’t have winners or losers at all. Games can involve physical exercise, computers, boards and dice, or just people telling stories. They can be played for fun, or for money, silly or deadly serious. Most have rules, but some don’t even have that. Instead, games are linked by history: a series of resemblances, people saying that “this” is a game because it’s kind of like “that”.
A subfield isn’t just a word, it’s a group of people. So subfields aren’t defined just by resemblance. Instead, they’re defined by practicality.
To ask what amplitudeology is really about, think about why you might want to call yourself an amplitudeologist. It could be a question of goals, certainly: you might care a lot about making better predictions for the LHC, or you could have some other grand story in mind about how amplitudes will save the world. Instead, though, it could be a matter of training: you learned certain methods, certain mathematics, a certain perspective, and now you apply it to your research, even if it goes further afield from what was considered “amplitudeology” before. It could even be a matter of community, joining with others who you think do cool stuff, even if you don’t share exactly the same goals or the same methods.
Calling yourself an amplitudeologist means you go to their conferences and listen to their talks, means you look to them to collaborate and pay attention to their papers. Those kinds of things define a subfield: not some grand mission statement, but practical questions of interest, what people work on and know and where they’re going with that. Instead of one story, like every other word, amplitudeology has a practical meaning that shifts and changes with time. That’s the way subfields should be: useful to the people who practice them.
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