Physics’ Unique Nightmare

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Halloween is coming up, so let’s talk about the most prominent monster of the physics canon, the nightmare scenario.

Not to be confused with the D&D Nightmare, which once was a convenient source of infinite consumable items for mid-level characters.

Right now, thousands of physicists search for more information about particle physics beyond our current Standard Model. They look at data from the Large Hadron Collider to look for signs of new particles and unexpected behavior, they try to detect a wide range of possible dark matter particles, and they make very precise measurements to try to detect subtle deviations. And in the back of their minds, almost all of those physicists wonder if they’ll find anything at all.

It’s not that we think the Standard Model is right. We know it has problems, deep mathematical issues that make it give nonsense answers and an apparent big mismatch with what we observe about the motion of matter and light in the universe. (You’ve probably heard this mismatch called dark matter and dark energy.)

But none of those problems guarantee an answer soon. The Standard Model will eventually fail, but it may fail only for very difficult and expensive experiments, not a Large Hadron Collider but some sort of galactic-scale Large Earth Collider. It might be that none of the experiments or searches or theories those thousands of physicists are working on will tell them anything they didn’t already know. That’s the nightmare scenario.

I don’t know another field that has a nightmare scenario quite like this. In most fields, one experiment or another might fail, not just not giving the expected evidence but not teaching anything new. But most experiments teach us something new. We don’t have a theory, in almost any field, that has the potential to explain every observation up to the limits of our experiments, but which we still hope to disprove. Only the Standard Model is like that.

And while thousands of physicists are exposed to this nightmare scenario, the majority of physicists aren’t. Physics isn’t just the science of the reductionistic laws of the smallest constituents of matter. It’s also the study of physical systems, from the bubbling chaos of nuclear physics to the formation of planets and galaxies and black holes, to the properties of materials to the movement of bacteria on a petri dish and bees in a hive. It’s also the development of new methods, from better control of individual atoms and quantum states to powerful new tricks for calculation. For some, it can be the discovery, not of reductionistic laws of the smallest scales, but of general laws of the largest scales, of how systems with many different origins can show echoes of the same behavior.

Over time, more and more of those thousands of physicists break away from the nightmare scenario, “waking up” to new questions of these kinds. For some, motivated by puzzles and skill and the beauty of physics, the change is satisfying, a chance to work on ideas that are moving forward, connected with experiment or grounded in evolving mathematics. But if your motivation is really tied to those smallest scales, to that final reductionistic “why”, then such a shift won’t be satisfying, and this is a nightmare you won’t wake up from.

Me, I’m not sure. I’m a tool-builder, and I used to tell myself that tool-builders are always needed. But I find I do care, in the end, what my tools are used for. And as we approach the nightmare scenario, I’m not at all sure I know how to wake up.

Neutrinos and Guarantees

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The Higgs boson, or something like it, was pretty much guaranteed.

When physicists turned on the Large Hadron Collider, we didn’t know exactly what they would find. Instead of the Higgs boson, there might have been many strange new particles with different properties. But we knew they had to find something, because without the Higgs boson or a good substitute, the Standard Model is inconsistent. Try to calculate what would happen at the LHC using the Standard Model without the Higgs boson, and you get literal nonsense: chances of particles scattering that are greater than one, a mathematical impossibility. Without the Higgs boson, the Standard Model had to be wrong, and had to go wrong specifically when that machine was turned on. In effect, the LHC was guaranteed to give a Nobel prize.

The LHC also searches for other things, like supersymmetric partner particles. It, and a whole zoo of other experiments, also search for dark matter, narrowing down the possibilities. But unlike the Higgs, none of these searches for dark matter or supersymmetric partners is guaranteed to find something new.

We’re pretty certain that something like dark matter exists, and that it is in some sense “matter”. Galaxies rotate, and masses bend light, in a way that seems only consistent with something new in the universe we didn’t predict. Observations of the whole universe, like the cosmic microwave background, let us estimate the properties of this something new, finding it to behave much more like matter than like radio waves or X-rays. So we call it dark matter.

But none of that guarantees that any of these experiments will find dark matter. The dark matter particles could have many different masses. They might interact faintly with ordinary matter, or with themselves, or almost not at all. They might not technically be particles at all. Each experiment makes some assumption, but no experiment yet can cover the most pessimistic possibility, that dark matter simply doesn’t interact in any usefully detectable way aside from by gravity.

Neutrinos also hide something new. The Standard Model predicts that neutrinos shouldn’t have mass, since it would screw up the way they mess with the mirror symmetry of the universe. But they do, in fact, have mass. We know because they oscillate, because they change when traveling, from one type to another, and that means those types must be mixes of different masses.

It’s not hard to edit the Standard Model to give neutrinos masses. But there’s more than one way to do it. Every way adds new particles we haven’t yet seen. And none of them tell us what neutrino masses should be. So there are a number of experiments, another zoo, trying to find out. (Maybe this one’s an aquarium?)

Are those experiments guaranteed to work?

Not so much as the LHC was to find the Higgs, but more than the dark matter experiments.

We particle physicists have a kind of holy book, called the Particle Data Book. It summarizes everything we know about every particle, and explains why we know it. It has many pages with many sections, but if you turn to page 10 of this section, you’ll find a small table about neutrinos. The table gives a limit: the neutrino mass is less than 0.8 eV (a mysterious unit called an electron-volt, about ten-to-the-minus-sixteen grams). That limit comes from careful experiments, using E=mc^2 to find what the missing mass could be when an electron-neutrino shoots out in radioactive beta decay. The limit is an inequality, “less than” rather than “equal to”, because the experiments haven’t detected any missing mass yet. So far, they only can tell us what they haven’t seen.

As these experiments get more precise, you could imagine them getting close enough to see some missing mass, and find the mass of a neutrino. And this would be great, and a guaranteed discovery, except that the neutrino they’re measuring isn’t guaranteed to have a mass at all.

We know the neutrino types have different masses, because they oscillate as they travel between the types. But one of the types might have zero mass, and it could well be the electron-neutrino. If it does, then careful experiments on electron-neutrinos may never give us a mass.

Still, there’s a better guarantee than for dark matter. That’s because we can do other experiments, to test the other types of neutrino. These experiments are harder to do, and the bounds they get are less precise. But if the electron neutrino really is massless, then we could imagine getting better and better at these different experiments, until one of them measures something, detecting some missing mass.

(Cosmology helps too. Wiggles in the shape of the universe gives us an estimate of the total, the mass of all the neutrinos averaged together. Currently, it gives another upper bound, but it could give a lower bound as well, which could be used along with weaker versions of the other experiments to find the answer.)

So neutrinos aren’t quite the guarantee the Higgs was, but they’re close. As the experiments get better, key questions will start to be answerable. And another piece of beyond-the-standard-model physics will be understood.

Academic Hiring: My Field vs. Bret’s

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Bret Deveraux is a historian and history-blogger who’s had a rough time on the academic job market. He recently had a post about how academic hiring works, at least in his corner of academia. Since we probably have some overlap in audience (and should have more, if you’re at all interested in ancient history he’s got some great posts), I figured I’d make a post of my own pointing out how my field, and fields nearby, do things differently.

First, there’s a big difference in context. The way Bret describes things, it sounds like he’s applying only to jobs in the US (maybe also Canada?). In my field, you can do that (the US is one of a few countries big enough to do that), but in practice most searches are at least somewhat international. If you look at the Rumor Mill, you’ll see a fair bit of overlap between US searches and UK searches, for example.

Which brings up another difference: rumor mills! It can be hard for applicants to get a clear picture of what’s going on. Universities sometimes forget to let applicants know they weren’t shortlisted, or even that someone else was hired. Rumor mills are an informal way to counteract this. They’re websites where people post which jobs are advertised in a given year, who got shortlisted, and who eventually got offered the job. There’s a rumor mill for the US market (including some UK jobs anyway), a UK rumor mill, a German/Nordic rumor mill (which also has a bunch of Italian jobs on it, to the seeming annoyance of the organizers), and various ones that I haven’t used but are linked on the US one’s page.

Bret describes a seasonal market with two stages: a first stage aimed at permanent positions, and a second stage for temporary adjunct teaching positions. My field doesn’t typically do adjuncts, so we just have the first stage. This is usually, like Bret’s field, something that happens in the Fall through Winter, but in Europe institutional funding decisions can get made later in the year, so I’ve seen new permanent positions get advertised even into the early Spring.

(Our temporary positions are research-focused, and advertised at basically the same time of year as the faculty positions, with the caveat that there is a special rule for postdocs. Due to a widely signed agreement, we in high-energy theory have agreed to not require postdocs to make a decision about whether they will accept a position until Feb 15 at the earliest. This stopped what used to be an arms race, with positions requiring postdocs to decide earlier and earlier in order to snatch the good ones before other places could make offers. The deadline was recently pushed a bit later yet, to lower administrative load during the Christmas break.)

Bret also describes two stages of interviews, a long-list interviewed on Zoom (that used to be interviewed at an important conference) and a short-list interviewed on campus. We just have the latter: while there are sometimes long-lists, they’re usually an internal affair, and I can’t think of a conference you could expect everyone to go to for interviews anyway. Our short-lists are also longer than his: I was among eight candidates when I interviewed for my position, which is a little high but not unheard of, five is quite typical.

His description of the actual campus visit matches my experience pretty well. There’s a dedicated talk, and something that resembles a “normal job interview”, but the rest, conversations from the drive in to the dinners if they organize them, are all interviews on some level too.

(I would add though, that while everyone there is trying to sort out if you’d be a good fit for them, you should also try to sort out if they’d be a good fit for you. I’ll write more about this another time, but I’m increasingly convinced that a key element in my landing a permanent position was the realization that, rather than just trying for every position I where I plausibly had a chance, I should focus on positions where I would actually be excited to collaborate with folks there.)

Bret’s field, as mentioned, has a “second round” of interviews for temporary positions, including adjuncts and postdocs. We don’t have adjuncts, but we do have postdocs, and they mostly interview at the same time the faculty do. For Bret, this wouldn’t make any sense, because anyone applying for postdocs is also applying for faculty positions, but in my field there’s less overlap. For one, very few people apply for faculty positions right out of their PhD: almost everyone, except those viewed as exceptional superstars, does at least one postdoc first. After that, you can certainly have collisions, with someone taking a postdoc and then getting a faculty job. The few times I’ve broached this possibility with people, they were flexible: most people have no hard feelings if a postdoc accepts a position and then changes their mind when they get a faculty job, and many faculty jobs let people defer a year, so they can do their postdoc and then start their faculty job afterwards.

(It helps that my field never seems to have all that much pressure to fill teaching roles. I’m not sure why (giant lecture courses using fewer profs? more research funding meaning we don’t have to justify ourselves with more undergrad majors?), but it’s probably part of why we don’t seem to hire adjuncts very often.)

Much like in Bret’s field, we usually need to submit a cover letter, CV, research statement, and letters of recommendation. Usually we submit a teaching statement, not a portfolio: some countries (Denmark) have been introducing portfolios but for now they’re not common. Diversity statements are broadly speaking a US and Canada thing: you will almost always need to submit one for a job in those places (one memorable job I looked at asserted that Italian-American counted as diversity), and sometimes in the UK, but much more rarely elsewhere in Europe (I can think of only one example). You never need to submit transcripts except if you’re applying to some unusually bureaucracy-obsessed country. “Writing samples” sometimes take the form of requests for a few important published papers: most places don’t ask for this, though. Our cover letters are less fixed (I’ve never heard a two-page limit, and various jobs actually asked for quite different things). While most jobs require three letters of recommendation, I was surprised to learn (several years in to applying…) that one sometimes can submit more, with three just being a minimum.

Just like Bret’s field, these statements all need to be tailored to the job to some extent (something I once again appreciated more a few years in). That does mean a lot of work, because much like Bret’s field there are often only a few reasonable permanent jobs one can apply for worldwide each year (maybe more than 6-12, but that depends on what you’re looking for), and they essentially all have hundreds of applicants. I won’t comment as much on how hiring decisions get made, except to say that my field seems a little less dysfunctional than Bret’s with “just out of PhD” hires quite rare and most people doing a few postdocs before finding a position. Still, there is a noticeable bias towards comparatively fresh PhDs, and this is reinforced by the European grant system: the ERC Starting Grant is a huge sum of money compared to many other national grants, and you can only apply for it within seven years from your PhD. The ERC Consolidator Grant can be applied for later (twelve years from PhD), but has higher standards (I’m working on an application for it this year). If you aren’t able to apply for either of those, then a lot of European institutions won’t consider you.

Congratulations to Pierre Agostini, Ferenc Krausz and Anne L’Huillier!

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The 2023 Physics Nobel Prize was announced this week, awarded to Pierre Agostini, Ferenc Krausz and Anne L’Huillier for figuring out how to generate extremely fast (hundreds of attoseconds) pulses of light.

Some physicists try to figure out the laws of physics themselves, or the behavior of big photogenic physical systems like stars and galaxies. Those people tend to get a lot of press, but most physicists don’t do that kind of work. Instead, most physicists try to accomplish new things with old physical laws: taking light, electrons, and atoms and doing things nobody thought possible. While that may sound like engineering, the work these physicists do lies beyond the bounds of what engineers are comfortable with: there’s too much uncertainty, too little precedent, and the applications are still far away. The work is done with the goal of pushing our capabilities as far as we can, accomplishing new things and worrying later about what they’re good for.

(Somehow, they still tend to be good for something, often valuable things. Knowing things pays off!)

Anne L’Huillier began the story in 1987, shining infrared lasers through noble gases and seeing the gas emit unexpected new frequencies. As physicists built on that discovery, it went from an academic observation to a more and more useful tool, until in 2001 Pierre Agostini and Ferenc Krausz, with different techniques both based on the same knowledge, managed to produce pulses of light only a few hundred attoseconds long.

(“Atto” is one of the SI prefixes. They go milli, micro, nano, pico, femto, atto. Notice that “nano” is in the middle there: an attosecond is as much smaller than a nanosecond as a nanosecond is from an ordinary second.)

This is cool just from the point of view of “humans doing difficult things”, but it’s also useful. Electrons move on attosecond time-scales. If you can send pulses of light at attosecond speed, you’ve got a camera fast enough to capture how electrons move in real time. You can figure out how they traverse electronics, or how they slosh back and forth in biological molecules.

This year’s prize has an extra point of interest for me, as both Anne L’Huillier and Pierre Agostini did their prize-winning work at CEA Paris-Saclay, where I just started work last month. Their groups would eventually evolve into something called Attolab, I walk by their building every day on the way to lunch.

On the Care and Feeding of International Employees

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Science and scholarship are global. If you want to find out the truth about the universe, you’ll have to employ the people best at figuring out that truth, regardless of where they come from. Research shuffles people around, driving them together to collaborate and apart to share their expertise.

(If you don’t care about figuring out the truth, and just want to make money? You still may want international employees. For plenty of jobs, the difference between the best person in the world and the best person in your country can be quite substantial.)

How do you get these international employees? You could pay them a lot, I guess, but that’s by definition expensive, and probably will annoy the locals. Instead, most of what you need to do to attract international employees isn’t to give them extra rewards: instead, it’s more important to level the playing field, and cover for the extra disadvantages an international employee will have.

You might be surprised when I mention disadvantages, but while international employees may be talented people, that doesn’t make moving to another country easy. If you stay in the same country you were born, you get involved in that country’s institutions in a regular way. Your rights and responsibilities, everything from driving to healthcare to taxes, are set up gradually over the course of your life. For someone moving to a new country, that means all of this has to be set up all at once.

This means that countries that can process these things quickly are much better for international employees. If your country takes six months to register someone for national healthcare, then new employees are at risk during that time or will have to pay extra for private insurance. If a national ID number is required to get a bank account, then whatever processing time that ID number takes must pass before the new employee can get paid. It also matters if the rules are clearly and consistently communicated, as new international employees can waste a lot of time and money if they’re given incorrect advice, or if different bureaucrats enforce different rules at their own discretion.

It also means that employers have an advantage if they can smooth entry into these institutions. In some countries it can be quite hard to find a primary care physician, as most people have the same doctor as their parents, switching only when a doctor retires. When I worked with the Perimeter Institute, they had a relationship with a local clinic that would accept their new employees as clients. In a city where it was otherwise quite hard to find a doctor, that was a real boon. Employers can also offer consistent advice even when their government doesn’t. They can keep track of their employees experiences and make reliable guides for how to navigate the system. If they can afford it, they can even keep an immigration lawyer on staff to advise about these questions.

An extremely important institution is the language itself. Moving internationally will often involve moving somewhere where you don’t speak the language, or don’t speak it very well. This gives countries an advantage if their immigrant-facing institutions are proficient in a language that’s common internationally, which at the moment largely means English. It also means countries have a big advantage if their immigrant-facing institutions are digital. If you communicate with immigrants with text, they can find online translations and at least try to figure things out. If you communicate in person, or worse through a staticky phone line, then you will try the patience even of people who do passably speak the language.

In the long term, of course, one cannot get by in one’s native language alone. As such, it is also important for countries to have good ways for people to learn the language. While I lived there, Denmark went back and forth on providing free language lessons for recent immigrants, sometimes providing them and sometimes not.

All of these things become twice as important in the case of spouses. You might think the idea that a country or employer should help out a new employee’s spouse is archaic, a product of an era of housewives discouraged from supporting themselves. But it is precisely because we don’t live in such an era that countries and employers need to take spouses into account. For an employer, hiring someone from another country is already an unusual event. Two partners getting hired to move to the same country by different employers at the same time is, barring special arrangements, extremely unlikely. That means that spouses of international employees should not have to wait for an employer to give them the same rights as their spouse: they need the same right to healthcare and employment and the like as their spouse, on arrival, so that they can find jobs and integrate without an unfair disadvantage. An employer can level the playing field further. The University of Copenhagen’s support for international spouses included social events (important because it’s hard to make new friends in a new country without the benefit of work friends), resume help (because each country has different conventions and expectations for job seekers), and even legal advice. At minimum, every resource you provide your employees that could in principle also be of use to their spouses (language classes, help with bureaucracy) should be considered.

In all your planning, as a country or an employer, keep in mind that not everyone has the same advantages. You can’t assume that someone moving to a new country will be able to integrate on their own. You have to help them, if not for fairness’ sake, then because if you don’t you won’t keep getting international employees to come at all.

Cause and Effect and Stories

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You can think of cause and effect as the ultimate story. The world is filled with one damn thing happening after another, but to make sense of it we organize it into a narrative: this happened first, and it caused that, which caused that. We tie this to “what if” stories, stories about things that didn’t happen: if this hadn’t happened, then it wouldn’t have caused that, so that wouldn’t have happened.

We also tell stories about cause and effect. Physicists use cause and effect as a tool, a criterion to make sense of new theories: does this theory respect cause and effect, or not? And just like everything else in science, there is more than one story they tell about it.

As a physicist, how would you think about cause and effect?

The simplest, and most obvious requirement, is that effects should follow their causes. Cause and effect shouldn’t go backwards in time, the cause should come before the effect.

This all sounds sensible, until you remember that in physics “before” and “after” are relative. If you try to describe the order of two distant events, your description will be different than someone moving with a different velocity. You might think two things happened at the same time, while they think one happened first, and someone else thinks the other happened first.

You’d think this makes a total mess of cause and effect, but actually everything remains fine, as long nothing goes faster than the speed of light. If someone could travel between two events slower than the speed of light, then everybody will agree on their order, and so everyone can agree on which one caused the other. Cause and effect only get screwed up if they can happen faster than light.

(If the two events are two different times you observed something, then cause and effect will always be fine, since you yourself can’t go faster than the speed of light. So nobody will contradict what you observe, they just might interpret it differently.)

So if you want to make sure that your theory respects cause and effect, you’d better be sure that nothing goes faster than light. It turns out, this is not automatic! In general relativity, an effect called Shapiro time delay makes light take longer to pass a heavy object than to go through empty space. If you modify general relativity, you can accidentally get a theory with a Shapiro time advance, where light arrives sooner than it would through empty space. In such a theory, at least some observers will see effects happen before their causes!

Once you know how to check this, as a physicist, there are two kinds of stories you can tell. I’ve heard different people in the field tell both.

First, you can say that cause and effect should be a basic physical principle. Using this principle, you can derive other restrictions, demands on what properties matter and energy can have. You can carve away theories that violate these rules, making sure that we’re testing for theories that actually make sense.

On the other hand, there are a lot of stories about time travel. Time travel screws up cause and effect in a very direct way. When Harry Potter and Hermione travel back in time at the end of Harry Potter and the Prisoner of Azkaban, they cause the event that saves Harry’s life earlier in the book. Science fiction and fantasy are full of stories like this, and many of them are perfectly consistent. How can we be so sure that we don’t live in such a world?

The other type of story positions the physics of cause and effect as a search for evidence. We’re looking for physics that violates cause and effect, because if it exists, then on some small level it should be possible to travel back in time. By writing down the consequences of cause and effect, we get to describe what evidence we’d need to see it breaking down, and if we see it whole new possibilities open up.

These are both good stories! And like all other stories in science, they only capture part of what the scientists are up to. Some people stick to one or the other, some go between them, driven by the actual research, not the story itself. Like cause and effect itself, the story is just one way to describe the world around us.

Stories Backwards and Forwards

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You can always start with “once upon a time”…

I come up with tricks to make calculations in particle physics easier. That’s my one-sentence story, or my most common one. If I want to tell a longer story, I have more options.

Here’s one longer story:

I want to figure out what Nature is telling us. I want to take all the data we have access to that has anything to say about fundamental physics, every collider and gravitational wave telescope and ripple in the overall structure of the universe, and squeeze it as hard as I can until something comes out. I want to make sure we understand the implications of our current best theories as well as we can, to as high precision as we can, because I want to know whether they match what we see.

To do that, I am starting with a type of calculation I know how to do best. That’s both because I can make progress with it, and because it will be important for making these inferences, for testing our theories. I am following a hint in a theory that definitely does not describe the real world, one that is both simpler to work with and surprisingly complex, one that has a good track record, both for me and others, for advancing these calculations. And at the end of the day, I’ll make our ability to infer things from Nature that much better.

Here’s another:

Physicists, unknowing, proposed a kind of toy model, one often simpler to work with but not necessarily simpler to describe. Using this model, they pursued increasingly elaborate calculations, and time and time again, those calculations surprised them. The results were not random, not a disorderly mess of everything they could plausibly have gotten. Instead, they had structure, symmetries and patterns and mathematical properties that the physicists can’t seem to explain. If we can explain them, we will advance our knowledge of models and theories and ideas, geometry and combinatorics, learning more about the unexpected consequences of the rules we invent.

We can also help the physicists advance physics, of course. That’s a happy accident, but one that justifies the money and time, showing the rest of the world that understanding consequences of rules is still important and valuable.

These seem like very different stories, but they’re not so different. They change in order, physics then math or math then physics, backwards and forwards. By doing that, they change in emphasis, in where they’re putting glory and how they’re catching your attention. But at the end of the day, I’m investigating mathematical mysteries, and I’m advancing our ability to do precision physics.

(Maybe you think that my motivation must lie with one of these stories and not the other. One is “what I’m really doing”, the other is a lie made up for grant agencies.
Increasingly, I don’t think people work like that. If we are at heart stories, we’re retroactive stories. Our motivation day to day doesn’t follow one neat story or another. We move forward, we maybe have deep values underneath, but our accounts of “why” can and will change depending on context. We’re human, and thus as messy as that word should entail.)

I can tell more than two stories if I want to. I won’t here. But this is largely what I’m working on at the moment. In applying for grants, I need to get the details right, to sprinkle the right references and the right scientific arguments, but the broad story is equally important. I keep shuffling that story, a pile of not-quite-literal index cards, finding different orders and seeing how they sound, imagining my audience and thinking about what stories would work for them.

Getting Started in Saclay

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I started work this week in my new position, as a permanent researcher at the Institute for Theoretical Physics of CEA Paris-Saclay. I’m still settling in, figuring out how to get access to the online system and food at the canteen and healthcare. Things are slowly getting into shape, with a lot of running around involved. Until then, I don’t have a ton of time to write (and am dedicating most of it to writing grants!) But I thought, mirroring a post I made almost a decade ago, that I’d at least give you a view of my new office.

Cosmology and the Laws of Physics

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Suppose you were an unusual sort of person: one who wanted, above all else, to know the laws of physics. Not content with the rules governing just one sort of thing, a star or an atom or a galaxy, you want to know the fundamental rules behind everything in the universe.

A good reductionist, you know that smaller things are more fundamental: the rules of the parts of things determine the rules of the whole. Knowing about quantum mechanics, you know that the more precisely you want to pin down something’s position, the more uncertain its momentum will be. And aware of special relativity, you know that terms like “small thing” or “high momentum” are relative: things can look bigger or smaller, faster or slower, depending on how they move relative to you. If you want to find the most fundamental things then, you end up needing not just small things or high momenta, but a lot of energy packed into a very small space.

You can get this in a particle collider, and that’s why they’re built. By colliding protons or electrons, you can cram a lot of energy into a very small space, and the rules governing that collision will be some of the most fundamental rules you have access to. By comparing your measurements of those collisions with your predictions, you can test your theories and learn more about the laws of physics.

If you really just wanted to know the laws of physics, then you might thing cosmology would be less useful. Cosmology is the science of the universe as a whole, how all of the stars and galaxies and the space-time around them move and change over the whole history of the universe. Dealing with very large distances, cosmology seems like it should take you quite far away from universal reductionist physical law.

If you thought that, you’d be missing one essential ingredient: the Big Bang. In the past, the universe was (as the song goes) in a hot dense state. The further back in time you look, the hotter and denser it gets. Go far enough back, and you find much higher energies, crammed into much smaller spaces, than we can make in any collider here on Earth. That means the Big Bang was governed by laws much more fundamental than the laws we can test here on Earth. And since the Big Bang resulted in the behavior of the universe as a whole, by observing that behavior we can learn more about those laws.

So a cosmologist can, in principle, learn quite a lot about fundamental physics. But cosmology is in many ways a lot harder than working with colliders. In a collider, we can clash protons together many times a second, with measurement devices right next to the collision. In cosmology, we have in a sense only one experiment, the universe we live in. We have to detect the evidence much later than the Big Bang itself, when the cosmic microwave background has cooled down and the structure of the universe has been warped by all the complexities of star and galaxy formation. Because we have only one experiment, all we can do is compare different sections of the sky, but there is only so much sky we can see, and as a consequence there are real limits on how much we can know.

Still, it’s worth finding out what we can know.m Cosmology is the only way at the moment we can learn about physics at very high energies, and thus learn the most fundamental laws. So if you’re someone who cares a lot about that sort of thing, it’s worth paying attention to!

Why You Might Want to Inspire Kids to Be Physicists (And What Movies You’d Make as a Result)

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Since the new Oppenheimer biopic came out, people have been making fun of this tweet by Sam Altman:

Expecting a movie about someone building an immensely destructive weapon, watching it plunge the world into paranoia, then getting mercilessly hounded about it to be an inspiration seems…a bit unrealistic? But everyone has already made that point. What I found more interesting was a blog post a couple days ago by science blogger Chad Orzel. Orzel asks, suppose you did want to make a movie inspiring kids to go into physics: how would you do it? I commented on his post with my own take on the question, then realized it might be nice as a post here.

If you want to inspire kids to go into physics with a movie, what do you do? Well, you can start by asking, why do you want kids to go into physics? Why do you want more physicists?

Maybe you believe that more physicists are needed to understand the fundamental laws of the universe. The quest of fundamental physics may be worthwhile in its own right, or may be important because understanding the universe gives us more tools to manipulate it. You might even think of Oppenheimer’s story in that way: because physicists understood the nature of the atom, they could apply that knowledge to change the world, racing to use it to defeat the Nazis and later convinced to continue to avoid a brutal invasion of Japan. (Whether the bomb was actually necessary to do this is still, of course, quite controversial.)

If that’s why you want more kids to be physicists, then you want a story like that. You could riff off of Ashoke Sen’s idea that physics may be essential to save humanity. The laws of physics appear to be unstable, such that at some point the world will shift and a “bubble”, expanding at the speed of light, will rewrite the rules in a way that would destroy all life as we know it. The only way to escape would be to travel faster than light, something that is possible because the universe itself expands at those speeds. By scattering “generation ships” in different directions, we could ensure that some of humanity would survive any such “bubble”: but only if we got the physics right.

A movie based on that idea could look a bit like the movie Cloud Atlas, with connected characters spanning multiple time periods. Scientists in the modern day investigate the expanding universe, making plans that refugees in a future generation ship must carry out. If you want to inspire kids with the idea that physics could save the world, you could get a lot of mileage out of a story that could actually be true.

On the other hand, maybe you don’t care so much about fundamental physics. Maybe you want more physicists because they’re good at solving a variety of problems. They help to invent new materials, to measure things precisely, to predict the weather, change computation, and even contribute to medicine. Maybe you want to tell a story about that.

(Maybe you even want these kids to go farther afield, and study physics without actually becoming physicists. Sam Altman is not a physicist, and I’ve heard he’s not very interested in directing his philanthropic money to increasing the number of jobs for physicists. On the other hand, the AI industry where he is a central player does hire a lot of ex-physicists.)

The problem, as Orzel points out, is that those stories aren’t really stories about physicists. They’re stories about engineering and technology, and a variety of other scientists, because a wide variety of people contribute to these problems. In order to tell a story that inspires people to be physicists, you need a story that highlights something unique that they bring to the table.

Orzel gets close to what I think of as the solution, by bringing up The Social Network. Altman was also mocked for saying that The Social Network motivated kids to found startups: the startup founders in that movie are not exactly depicted as good people. But in reality, it appears that the movie did motivate people to found startups. Stories about badass amoral jerks are engaging, and it’s easy to fantasize about having that kind of power and ability. There’s a reason that The Imitation Game depicted Alan Turing, a man known for his gentle kindness, as brusque and arrogant.

If you want to tell a story about physicists, it’s actually pretty easy, because physicists can be quite arrogant! There is a stereotype of physicists walking into another field, deciding they know everything they need to know, and lecturing the experts about how they should be doing their jobs. This really does happen, and sometimes it’s exactly as dumb as it sounds…but sometimes the physicists are right! Orzel brings up Feynman’s role in figuring out how the Challenger space shuttle blew up, an example of precisely this kind of success.

So if you want kids to grow up to be generalist physicists, people who solve all sorts of problems for all sorts of people, you need to tell them a story like that. One with a Sherlock-esque physicist who runs around showing how much smarter they are than everyone else. You need to make a plot where they physicist waves around “physicist tools”, like dimensional analysis, Fermi estimates, and thermodynamics, and uses them to uncover a mystery, showing a bunch of engineers or biologists just how much cooler they are.

If you do that, you probably could inspire some kids to become physicists. You’ll need a new movie to inspire them to be engineers or biologists, though!