# Why Physicists Leave Physics

It’s an open secret that many physicists end up leaving physics. How many depends on how you count things, but for a representative number, this report has 31% of US physics PhDs in the private sector after one year. I’d expect that number to grow with time post-PhD. While some of these people might still be doing physics, in certain sub-fields that isn’t really an option: it’s not like there are companies that do R&D in particle physics, astrophysics, or string theory. Instead, these physicists get hired in data science, or quantitative finance, or machine learning. Others stay in academia, but stop doing physics: either transitioning to another field, or taking teaching-focused jobs that don’t leave time for research.

There’s a standard economic narrative for why this happens. The number of students grad schools accept and graduate is much higher than the number of professor jobs. There simply isn’t room for everyone, so many people end up doing something else instead.

That narrative is probably true, if you zoom out far enough. On the ground, though, the reasons people leave academia don’t feel quite this “economic”. While they might be indirectly based on a shortage of jobs, the direct reasons matter. Physicists leave physics for a wide variety of reasons, and many of them are things the field could improve on. Others are factors that will likely be present regardless of how many students graduate, or how many jobs there are. I worry that an attempt to address physics attrition on a purely economic level would miss these kinds of details.

I thought I’d talk in this post about a few reasons why physicists leave physics. Most of this won’t be new information to anyone, but I hope some of it is at least a new perspective.

First, to get it out of the way: almost no-one starts a physics PhD with the intention of going into industry. I’ve met a grand total of one person who did, and he’s rather unusual. Almost always, leaving physics represents someone’s dreams not working out.

Sometimes, that just means realizing you aren’t suited for physics. These are people who feel like they aren’t able to keep up with the material, or people who find they aren’t as interested in it as they expected. In my experience, people realize this sort of thing pretty early. They leave in the middle of grad school, or they leave once they have their PhD. In some sense, this is the healthy sort of attrition: without the ability to perfectly predict our interests and abilities, there will always be people who start a career and then decide it’s not for them.

I want to distinguish this from a broader reason to leave, disillusionment. These are people who can do physics, and want to do physics, but encounter a system that seems bent on making them do anything but. Sometimes this means disillusionment with the field itself: phenomenologists sick of tweaking models to lie just beyond the latest experimental bounds, or theorists who had hoped to address the real world but begin to see that they can’t. This kind of motivation lay behind several great atomic physicists going into biology after the second world war, to work on “life rather than death”. Sometimes instead it’s disillusionment with academia: people who have been bludgeoned by academic politics or bureaucracy, who despair of getting the academic system to care about real research or teaching instead of its current screwed-up priorities or who just don’t want to face that kind of abuse again.

When those people leave, it’s at every stage in their career. I’ve seen grad students disillusioned into leaving without a PhD, and successful tenured professors who feel like the field no longer has anything to offer them. While occasionally these people just have a difference of opinion, a lot of the time they’re pointing out real problems with the system, problems that actually should be fixed.

Sometimes, life intervenes. The classic example is the two-body problem, where you and your spouse have trouble finding jobs in the same place. There aren’t all that many places in the world that hire theoretical physicists, and still fewer with jobs open. One or both partners end up needing to compromise, and that can mean switching to a career with a bit more choice in location. People also move to take care of their parents, or because of other connections.

This seems closer to the economic picture, but I don’t think it quite lines up. Even if there were a lot fewer physicists applying for the same number of jobs, it’s still not certain that there’s a job where you want to live, specifically. You’d still end up with plenty of people leaving the field.

A commenter here frequently asks why physicists have to travel so much. Especially for a theorist, why can’t we just work remotely? With current technology, shouldn’t that be pretty easy to do?

I’ve done a lot of remote collaboration, it’s not impossible. But there really isn’t a substitute for working in the same place, for being able to meet someone in the hall and strike up a conversation around a blackboard. Remote collaborations are an ok way to keep a project going, but a rough way to start one. Institutes realize this, which is part of why most of the time they’ll only pay you a salary if they think you’re actually going to show up.

Could I imagine this changing? Maybe. The technology doesn’t exist right now, but maybe someday someone will design a social network with the right features, one where you can strike up and work on collaborations as naturally as you can in person. Then again, maybe I’m silly for imagining a technological solution to the problem in the first place.

What about more direct economic reasons? What about when people leave because of the academic job market itself?

This certainly happens. In my experience though, a lot of the time it’s pre-emptive. You’d think that people would apply for academic jobs, get rejected, and quit the field. More often, I’ve seen people notice the competition for jobs and decide at the outset that it’s not worth it for them. Sometimes this happens right out of grad school. Other times it’s later. In the latter case, these are often people who are “keeping up”, in that their career is moving roughly as fast as everyone else’s. Rather, it’s the stress, of keeping ahead of the field and marketing themselves and applying for every grant in sight and worrying that it could come crashing down any moment, that ends up too much to deal with.

What about the people who do get rejected over and over again?

Physics, like life in Jurassic Park, finds a way. Surprisingly often, these people manage to stick around. Without faculty positions they scrabble up postdoc after postdoc, short-term position after short-term position. They fund their way piece by piece, grant by grant. Often they get depressed, and cynical, and pissed off, and insist that this time they’re just going to quit the field altogether. But from what I’ve seen, once someone is that far in, they often don’t go through with it.

If fewer people went to physics grad school, or more professors were hired, would fewer people leave physics? Yes, absolutely. But there’s enough going on here, enough different causes and different motivations, that I suspect things wouldn’t work out quite as predicted. Some attrition is here to stay, some is independent of the economics. And some, perhaps, is due to problems we ought to actually solve.

# Thoughts on Polchinski’s Memoir

I didn’t get a chance to meet Joseph Polchinski when I was visiting Santa Barbara last spring. At the time, I heard his health was a bit better, but he still wasn’t feeling well enough to come in to campus. Now that I’ve read his memoir, I almost feel like I have met him. There’s a sense of humor, a diffidence, and a passion for physics that shines through the pages.

The following are some scattered thoughts inspired by the memoir:

A friend of mine once complained to me that in her field grad students all brag about the colleges they went to. I mentioned that in my field your undergrad never comes up…unless it was Caltech. For some reason, everyone I’ve met who went to Caltech is full of stories about the place, and Polchinski is no exception. Speaking as someone who didn’t go there, it seems like Caltech has a profound effect on its students that other places don’t.

Polchinski mentions hearing stories about geniuses of the past, and how those stories helped temper some of his youthful arrogance. There’s an opposite effect that’s also valuable: hearing stories like Polchinski’s, his descriptions of struggling with anxiety and barely publishing and “not really accomplishing anything” till age 40, can be a major comfort to those of us who worry we’ve fallen behind in the academic race. That said, it’s important not to take these things too far: times have changed, you’re not Polchinski, and much like his door-stealing trick at Caltech getting a postdoc without any publications is something you shouldn’t try at home. Even Witten’s students need at least one.

Last week I was a bit puzzled by nueww’s comment, a quote from Polchinski’s memoir which distinguishes “math of the equations” from “math of the solutions”, attributing the former to physicists and the latter to mathematicians. Reading the context in the memoir and the phrase’s origin in a remark by Susskind cleared up a bit, but still left me uneasy. I only figured out why after Lubos Motl posted about it: it doesn’t match my experience of mathematicians at all!

If anything, I think physicists usually care more about the “solutions” than mathematicians do. In my field, often a mathematician will construct some handy basis of functions and then frustrate everyone by providing no examples of how to use them. In the wider math community I’ve met graph theorists who are happy to prove something is true for all graphs of size $10^{10^10}$ and larger, not worrying about the vast number of graphs where it fails because it’s just a finite number of special cases. And I don’t think this is just my experience: a common genre of jokes revolve around mathematicians proving a solution exists and then not bothering to do anything with it (for example, see the joke with the hotel fire here).

I do think there’s a meaningful sense in which mathematicians care about details that we’re happy to ignore, but “solutions” versus “equations” isn’t really the right axis. It’s something more like “rigor” versus “principles”. Mathematicians will often begin a talk by defining a series of maps between different spaces, carefully describing where they are and aren’t valid. A physicist might just write down a function. That sort of thing is dangerous in mathematics: there are always special, pathological cases that make careful definitions necessary. In physics, those cases rarely come up, and when they do there’s often a clear physical problem that brings them to the forefront. We have a pretty good sense of when we need rigor, and when we don’t we’re happy to lay things out without filling in the details, putting a higher priority on moving forward and figuring out the basic principles underlying reality.

Polchinski talks a fair bit about his role in the idea of the multiverse, from hearing about Weinberg’s anthropic argument to coming to terms with the string landscape. One thing his account makes clear is how horrifying the concept seemed at first: how the idea that the parameters of our universe might just be random could kill science and discourage experimentalists. This touches on something that I think gets lost in arguments about the multiverse: even the people most involved in promoting the multiverse in public aren’t happy about it.

It also sharpened my thinking about the multiverse a bit. I’ve talked before about how I don’t think the popularity of the multiverse is actually going to hurt theoretical physics as a field. Polchinski’s worries made me think about the experimental side of the equation: why do experiments if the world might just be random? I think I have a clearer answer to this now, but it’s a bit long, so I’ll save it for a future post.

One nice thing about these long-term accounts is you get to see how much people shift between fields over time. Polchinski didn’t start out working in string theory, and most of the big names in my field, like Lance Dixon and David Kosower, didn’t start out in scattering amplitudes. Academic careers are long, and however specialized we feel at any one time we can still get swept off in a new direction.

I’m grateful for this opportunity to “meet” Polchinski, if only through his writing. His is a window on the world of theoretical physics that is all too rare, and valuable as a result.

# Next Year in Copenhagen!

As some of you might be aware, this is my last year at the Perimeter Institute. It’s been great, but the contract was only for three years, and come August I’ll be heading elsewhere.

Determining that “elsewhere” was the subject of an extensive job search. Now that the search has resolved, I can tell you that “elsewhere” is the Niels Bohr International Academy at the Niels Bohr Institute in Copenhagen, where I’ll be starting a three-year postdoc job in the fall.

Probably in the building on the left

There are some pretty stellar amplitudes people at NBIA, so I’m pretty excited to be going there. It’s going to be a great opportunity to both build on what I’ve been doing and expand beyond. They’re also hiring several other amplitudes-focused postdocs this year, so overall it should be a really fun group.

It’s also a bit daunting. Moving to Canada from the US was reasonably smooth, I could drive most of my things over in a U-Haul truck. Moving to Denmark is going to be quite a bit more complicated. I’ll need to learn a new language and get used to a fairly different culture.

I can take solace in the fact that in some sense I’m retracing my great-grandfather’s journey in the opposite direction. My great-grandfather worked at the Niels Bohr Institute on his way out of Europe in the 1930’s, and made friends with the Bohrs along the way, before coming to the US. I’ll get a chance to explore a piece of family history, and likely collaborate with a Bohr as well.

# Perimeter!

I’m moving in at Perimeter this week, so I don’t have time to write a long post. For those who aren’t familiar with it, the Perimeter Institute for Theoretical Physics is an independent research institute, not affiliated with any university. Instead, it’s funded by a combination of government and private sources (for why private sources might fund theoretical physics, read my discussion here). Because it’s not a university they have budgets to do things like hire people to make the transition process easier, so everything has been really nice and well-organized.

The postdoc offices are really nice, with a view of the nearby park, shown below.

On the Perimeter…of Waterloo Park

# Stop! Impostor!

Ever felt like you don’t belong? Like you don’t deserve to be where you are, that you’re just faking competence you don’t really have?

If not, it may surprise you to learn that this is a very common feeling among successful young academics. It’s called impostor syndrome, and it happens to some very talented people.

It’s surprisingly easy to rationalize success as luck, to assume praise comes from people who don’t know the full story. In science, we’re surrounded by people who seem to come up with brilliant insights on a regular basis. We see others’ successes far more often than we see their failures, and often we forget that science is at its heart a process of throwing ideas against a wall until something sticks. Hyper-aware of our own failures, when we present ourselves as successful we can feel like we’re putting on a paper-thin disguise, constantly at risk that someone will see through it.

As paper-thin disguises go, I prefer the classics.

In my experience, theoretical physics is especially heavy on impostor syndrome, for a number of reasons.

First, there’s the fact that beginning grad students really don’t know all they need to. Theoretical physics requires a lot of specialized knowledge, and most grad students just have the bare bones basics of a physics undergrad degree. On the strength of those basics, you’re somehow supposed to convince a potential advisor, an established, successful scientist, that you’re worth paying attention to.

Throw in the fact that many people have a little more than the basics, whether from undergrad research projects or grad-level courses taken early, and you have a group where everyone is trying to seem more advanced than they are. There’s a very real element of fake it till you make it, of going to talks and picking up just enough of the lingo to bluff your way through a conversation.

And the thing is, even after you make it, you’ll probably still feel like you’re faking it.

As I’ve mentioned before, there’s an enormous amount of jury-rigging that goes into physics research. There are a huge number of side-disciplines that show up at one point or another, from numerical methods to programming to graphic design. We can’t hire a professional to handle these things, we have to learn them ourselves. As such, we become minor dabblers in a whole mess of different fields. Work on something enough and others will start looking to you for help. It won’t feel like you’re an expert, though, because you know in the back of your mind that the real experts know so much more.

In the end, the best approach I’ve found is simply to keep saying yes. Keep using what you know, going to talks and trying new things. The more you “pretend” to know what you’re doing, the more experience you’ll get, until you really do know what you’re doing. There’s always going to be more to learn, but chances are if you’re feeling impostor syndrome you’ve already learned a lot. Take others’ opinions of you at face value, and see just how far you can go.

# The Many (Body) Problems of the Academic Lifestyle

I’m visiting Perimeter this week, searching for apartments in the area. This got me thinking about how often one has to move in academia. You move for college, you move for grad school, you move for each postdoc job, and again when you start as a professor. Even then, you may not get to stay where you are if you don’t manage to get tenure, and it may be healthier to resign yourself to moving every seven years rather than assuming you’re going to settle down.

Most of life isn’t built around the idea that people move across the country (or the world!) every 2-7 years, so naturally this causes a few problems for those on the academic path. Below are some well-known, and not-so-well-known, problems facing academics due to their frequent relocations:

The two-body problem:

Suppose you’re married, or in a committed relationship. Better hope your spouse has a flexible job, because in a few years you’re going to be moving to another city. This is even harder if your spouse is also an academic, as that requires two rare academic jobs to pop up in the same place. And woe betide you if you’re out of synch, and have to move at different times. Many couples end up having to resort to some sort of long-distance arrangement, which further complicates matters.

The N-body problem:

Like the two-body problem, but for polyamorous academics. Leads to poly-chains up and down the East Coast.

The 2+N-body problem:

Alternatively, add a time dimension to your two-body problem via the addition of children. Now your kids are busily being shuffled between incommensurate school systems. But you’re an academic, you can teach them anything they’re missing, right?

The warm body problem:

Of course, all this assumes you’re in a relationship. If you’re single, you instead have the problem of never really having a social circle beyond your department, having to tenuously rebuild your social life every few years. What sorts of clubs will the more socially awkward of you enter, just to have some form of human companionship?

The large body of water problem:

We live in an age where everything is connected, but that doesn’t make distance cheap. An ocean between you and your collaborators means you’ll rarely be awake at the same time. And good luck crossing that ocean again, not every job will be eager to pay relocation expenses.

The obnoxious governing body problem:

Of course, the various nations involved won’t make all this travel easy. Many countries have prestigious fellowships only granted on the condition that the winner returns to their home country for a set length of time. Since there’s no guarantee that anyone in your home country does anything similar to what you do, this sort of requirement can have people doing whatever research they can find, however tangentially related, or trying to avoid the incipient bureaucratic nightmare any way they can.

# Four Gravitons and a…Postdoc?

As a few of you already know, it’s looking increasingly certain that I will be receiving my Ph.D. in the spring. I’ll graduate, ceasing to be a grad student and becoming that most mysterious of academic entities, a postdoc.

When describing graduate school before, I compared it to an apprenticeship. (I expanded on that analogy more here.) Let’s keep pursuing that analogy. If a graduate student is like an apprentice, then a Postdoctoral Scholar, or Postdoc, is like a journeyman.

In Medieval Europe, once an apprenticeship was completed the apprentice was permitted to work independently, earning a wage for their own labors. However, they still would not have their own shop. Instead, they would work for a master craftsman. Such a person was called a journeyman, after the French work journée, meaning a day’s work.

Similarly, once a graduate student gets their Ph.D., they are able to do scientific research independently. However, most graduate students are not ready to be professors when fresh out of their Ph.D. Instead, they become postdocs, working in an established professor’s group. Like a journeyman, a postdoc is nominally independent, but in practice works under loose supervision from the more mature members of their field.

Another similarity between postdocs and journeymen is their tendency to travel. Historically, a journeyman would spend several years traveling, studying in the workshops of several masters. Similarly, a postdoc will often (especially in today’s interconnected world) travel far from where they began in order to broaden their capabilities.

A postdoctoral job generally lasts two or three years, one for particularly short positions. Most scientists will go through at least one postdoctoral position after achieving their Ph.D. In some fields (theoretical physics in particular), a scientist will have two or three such positions in different places before finding a job as a professor. Postdocs are paid significantly better than grad students, but generally significantly worse than professors. They don’t (typically) teach, but depending on the institution and field they may do some TA work.

Being still a grad student, my blog is titled “4 gravitons and a grad student”. That could change, though. Once I become a postdoc, I have three options:

1. Keep the old title. Keeping the same title and domain name makes it easier for people to find the blog. It also maintains the alliteration, which I think is fun. On the other hand, it would be hard to justify, and I’d likely have to write something silly about taking a grad student perspective or the like.
2. Change to “4 gravitons and a postdoc”. I’d lose the fun alliteration, but the title would accurately represent my current state. However, I might lose a few readers who don’t expect the change.
3. Cut it down to “4 gravitons”. This matches the blog’s twitter handle (@4gravitons). It’s quick, it’s recognizable, and it keeps the memorable part of the old title without adding anything new to remember. However, it would be less unique in google searches.

What do you folks think? I’ve still got a while to decide, and I’d love to hear your opinions!