Tag Archives: academia

The Royal We of Theoretical Physics

I’m about to show you an abstract from a theoretical physics paper. Don’t worry about what it says, just observe the grammar.

wittenabstract

Notice anything? Here, I’ll zoom in:

wittenwe

This paper has one author, Edward Witten. So who’s “we”?

As it turns out, it is actually quite common in theoretical physics for a paper to use the word “we”, even when it is written by a single author. While this tradition has been called stilted, pompous, and just plain bad writing, there is a legitimate reason behind it. “We” is convenient, because it represents several different important things.

While the paper I quoted was written by only one author, many papers are collaborative efforts. For a collaboration, depending on collaboration style, it is often hard to distinguish who did what in a consistent way. As such, “we” helps smooth over different collaboration styles in a consistent way.

What about single-authored papers, though? For a single author, and often even for multiple authors, “we” means the author plus the reader.

In principle, anyone reading a paper in theoretical physics should be able to follow along, doing the calculations on their own, and replicate the paper’s results. In practice this can often be difficult to impossible, but it’s still true that if you want to really retain what you read in theoretical physics, you need to follow along and do some of the calculation yourself. As a nod to this, it is conventional to write theoretical physics papers as if the reader was directly participating, leading them through the results point by point like exercises in a textbook. “We” do one calculation, then “we” use the result to derive the next point, and so on.

There are other meanings that “we” can occasionally serve, such as referring to everyone in a particular field, or a group in a hypothetical example.

While each of these meanings of “we” could potentially use a different word, that tends to make a paper feel cluttered, with jarring transitions between different subjects. Using “we” for everything gives the paper a consistent voice and feel, though it does come at the cost of obscuring some of the specific details of who did what. Especially for collaborations, the “we the collaborators” and “we the author plus reader” meanings can overlap and blur together. This usually isn’t a problem, but as I’ve been finding out recently it does make things tricky when writing for people who aren’t theoretical physicists, such as universities with guidelines that require a thesis to clearly specify who in a collaboration did what.

On an unrelated note, two papers went up this week pushing the hexagon function story to new and impressive heights. I wasn’t directly involved in either, I’ve been attacking a somewhat different part of the problem, and you can look forward to something on that in a few months.

What’s in a Thesis?

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As I’ve mentioned before, I’m graduating this spring, which means I need to write that most foreboding of documents, the thesis. As I work on it, I’ve been thinking about how the nature of the thesis varies from field to field.

If you don’t have much experience with academics, you probably think of a thesis as a single, overarching achievement that structures a grad student’s career. A student enters grad school, designs an experiment, performs it, collects data, analyzes the data, draws some conclusion, then writes a thesis about it and graduates.

In some fields, the thesis really does work that way. In biology for example, the process of planning an experiment, setting it up, and analyzing and writing up the data can be just the right size so that, a reasonable percentage of the time, it really can all be done over the course of a PhD.

Other fields tend more towards smaller, faster-paced projects. In theoretical physics, mathematics, and computer science, most projects don’t have the same sort of large experimental overhead that psychologists or biologists have to deal with. The projects I’ve worked on are large-scale for theoretical physics, and I’ll still likely have worked on three distinct things before I graduate. Others, with smaller projects, will often have covered more.

In this situation, a thesis isn’t one overarching idea. Rather, it’s a compilation of work from past projects, sewed together with a pretense of an overall theme. It’s a bit messy, but because it’s the way things are expected to be done in these fields, no-one minds particularly much.

The other end of the spectrum is potentially much harder to deal with. For those who work on especially big experiments, the payoff might take longer to arrive than any reasonable degree. Big machines like colliders and particle detectors can take well over a decade before they start producing data, while longitudinal studies that follow a population as they grow and age take a long time no matter how fast you work.

In cases like this, the challenge is to chop off a small enough part of the project to make it feel like a thesis. A thesis could be written about designing one component for the eventual machine, or analyzing one part of the vast sea of data it produces. Preliminary data from a longitudinal study could be analyzed, even when the final results are many years down the line.

People in these fields have to be flexible and creative when it comes to creating a thesis, but usually the thesis committee is reasonable. In the end, a thesis is what you need to graduate, whatever that actually is for you.

Four Gravitons and a…Postdoc?

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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:

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.
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.
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!

Amplitudes on Paperscape

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Paperscape is a very cool tool developed by Damien George and Rob Knegjens. It analyzes papers from arXiv, the paper repository where almost all physics and math papers live these days. By putting papers that cite each other closer together and pushing papers that don’t cite each other further apart, Paperscape creates a map of all the papers on arXiv, arranged into “continents” based on the links between them. Papers with more citations are shown larger, newer papers are shown brighter, and subject categories are indicated by color-coding.

Here’s a zoomed-out view:

Already you can see several distinct continents, corresponding to different arXiv categories like high energy theory and astrophysics.

If you want to find amplitudes on this map, just zoom in between the purple continent (high energy theory, much of which is string theory) and the green one (high energy lattice, nuclear experiment, high energy experiment, and high energy phenomenology, broadly speaking these are all particle physics).

When you zoom in, Paperscape shows words that commonly appear in a given region of papers. Zoomed in this far, you can see amplitudes!

Amplitudeologists like me live on an island between particle physics and string theory. We’re connected on both sides by bridges of citations and shared terms, linking us to people who study quarks and gluons on one side to people who study strings and geometry on the other. Think of us like Manhattan, an island between two shores, densely networked in to the surroundings.

Zoom in further, and you can see common keywords for individual papers. Exploring around here shows not only what is getting talked about, but what sort of subjects as well. You can see by the color-coding that many papers in amplitudes are published as hep-th, or high energy theory, but there’s a fair number of papers from hep-ph (phenomenology) and from nuclear physics as well.

There’s a lot of interesting things you can do with Paperscape. You can search for individuals, or look at individual papers, seeing who they cite and who cite them. Try it out!

Where are the Amplitudeologists?

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As I’ve mentioned a couple of times before, I’m part of a sub-field of theoretical physics called Amplitudeology.

Amplitudeology in its modern incarnation is relatively new, and concentrated in a few specific centers. I thought it might be interesting to visualize which universities have amplitudeologists, so I took a look at the attendee lists of two recent conferences and put their affiliations into google maps. In an attempt to balance things, one of the conferences is in North America and the other is in Europe. Here is the result:

The West Coast of the US has two major centers, Stanford/SLAC and UCLA, focused around Lance Dixon and Zvi Bern respectively. The Northeast has a fair assortment, including places that have essentially everything like the Perimeter Institute and the Institute for Advanced Study and places known especially for their amplitudes work like Brown.

Europe has quite a large number of places. There are many universities in Europe with a long history of technical research into quantum field theory. When amplitudes began to become more prominent as its own sub-field, many of these places slotted right in. In particular, there are many locations in Germany, a decent number in the UK, a few in the vicinity of CERN, and a variety of places of some importance elsewhere.

Outside of Europe and North America, there’s much less amplitudes research going on. Physics in general is a very international enterprise, and many sub-fields have a lot of participation from researchers in China, India, Japan, and Korea. Amplitudes, for the most part, hasn’t caught on in those places yet.

This map is just a result of looking at two conferences. More data would yield many places that were left out of this setup, including a longstanding community in Russia. Still, it gives you a rough idea of where to find amplitudeologists, should you have need of one.

What’s up with arXiv?

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First of all, I wanted to take a moment to say that this is the one-year anniversary of this blog. I’ve been posting every week, (almost always) on Friday, since I first was motivated to start blogging back in November 2012. It’s been a fun ride, through ups and downs, Ars Technica and Amplituhedra, and I hope it’s been fun for you, the reader, as well!

I’ve been giving links to arXiv since my very first post, but I haven’t gone into detail about what arXiv is. Since arXiv is a rather unique phenomenon, it could use a more full description.

The word arXiv is pronounced much like the normal word archive, just think of the capital X like a Greek letter Chi.

Much as the name would suggest, arXiv is an archive, specifically a preprint archive. A pre-print is in a sense a paper before it becomes a paper; more accurately, it is a scientific paper that has not yet been published in a journal. In the past, such preprints would be kept by individual universities, or passed between interested individuals. Now arXiv, for an increasing range of fields (first physics and mathematics, now also computer science, quantitative biology, quantitative finance, and statistics) puts all of the preprints in one easily accessible, free to access place.

Different fields have different conventions when it comes to using arXiv. As a theoretical physicist, I can only really speak to how we use the system.

When theoretical physicists write a paper, it is often not immediately clear which journal we should submit it to. Different journals have different standards, and a paper that will gather more interest can be published in a more prestigious journal. In order to gauge how much interest a paper will raise, most theoretical physicists will put their papers up on arXiv as preprints first, letting them sit there for a few months to drum up attention and get feedback before formally submitting the paper to a journal.

The arXiv isn’t just for preprints, though. Once a paper is published in a journal, a copy of the paper remains on arXiv. Often, the copy on arXiv will be updated when the paper is updated, changed to the journal’s preferred format and labeled with the correct journal reference. So arXiv, ultimately, contains almost all of the papers published in theoretical physics in the last decade or two, all free to read.

But it’s not just papers! The digital format of arXiv makes it much easier to post other files alongside a paper, so that many people upload not just their results, but the computer code they used to generate them, or their raw data in long files. You can also post papers too long or unwieldy to publish in a journal, making arXiv an excellent dropping-off point for information in whatever format you think is best.

We stand at the edge of a new age of freely accessible science. As more and more disciplines start to use arXiv and similar services, we’ll have more flexibility to get more information to more people, while still keeping the advantage of peer review for publication in actual journals. It’s going to be very interesting to see where things go from here.

Blackboards, Again

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Recently I had the opportunity to give a blackboard talk. I’ve talked before about the value of blackboards, how they facilitate collaboration and can even be used to get work done. What I didn’t feel the need to explain was their advantages when giving a talk.

No, the blackboard behind me isn’t my talk.

When I mentioned I was giving a blackboard talk, some of my friends in other fields were incredulous.

“Why aren’t you using PowerPoint? Do you people hate technology?”

So why do theorists (and mathematicians) do blackboard talks, when many other fields don’t?

Typically, a chemist can’t bring chemicals to a talk. A biologist can’t bring a tank of fruit flies or zebrafish, and a psychologist probably shouldn’t bring in a passel of college student test subjects. As a theorist though, our test subjects are equations, and we can absolutely bring them into the room.

In the most ideal case, a talk by a theorist walks you through their calculation, reproducing it on the blackboard in enough detail that you can not only follow along, but potentially do the calculation yourself. While it’s possible to set up a calculation step by step in PowerPoint, you don’t have the same flexibility to erase and add to your equations, which becomes especially important if you need to clarify a point in response to a question.

Blackboards also often give you more space than a single slide. While your audience still only pays attention to a slide-sized area of the board at one time, you can put equations up in one area, move away, and then come back to them later. If you leave important equations up, people can remind themselves of them on their own time, without having to hold everybody up while you scroll back through the slides to the one they want to see.

Using a blackboard well is a fine art, and one I’m only beginning to learn. You have to know what to erase and what to leave up, when to pause to allow time to write or ask questions, and what to say while you’re erasing the board. You need to use all the quirks of the medium to your advantage, to show people not just what you did, but how and why you did it.

That’s why we use blackboards. And if you ask why we can’t do the same things with whiteboards, it’s because whiteboards are terrible. Everybody knows that.

Dammit Jim, I’m a Physicist not a Graphic Designer!

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Over the last week I’ve been working with a few co-authors to get a paper ready for publication. For my part, this has mostly meant making plots of our data. (Yes, theorists have data! It’s the result of calculations, not observations, but it’s still data!)

As it turns out, making the actual plots is only the first and easiest step. We have a huge number of data points, which means the plots ended up being very large files. To fix this I had to smooth out the files so they don’t include every point, a process called rasterizing the images. I also needed to make sure that the labels of the plots matched the fonts in the paper, and that the images in the paper were of the right file type to be included, which in turn meant understanding the sort of information retained by each type of image file. I had to learn which image files include transparency and which don’t, which include fonts as text and which use images, and which fonts were included in each program I used. By the end, I learned more about graphic design than I ever intended to.

In a company, this sort of job would be given to a graphic designer on-staff, or a hired expert. In academia, however, we don’t have the resources for that sort of thing, so we have to become experts in the nitty-gritty details of how to get our work in publishable form.

As it turns out, this is part of a wider pattern in academia. Any given project doesn’t have a large staff of specialists or a budget for outside firms, so everyone involved has to become competent at tasks that a business would parcel out to experts. This is why a large part of work in physics isn’t really physics per se; rather, we theorists often spend much of our time programming, while experimentalists often have to build and repair their experimental apparatus. The end result is that much of what we do is jury-rigged together, with an amateur understanding of most of the side disciplines involved. Things work, but they aren’t as efficient or as slick as they could be if assembled by a real expert. On the other hand, it makes things much cheaper, and it’s a big contributor to the uncanny ability of physicists to know about other peoples’ disciplines.

Talks, and what they’re good for

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It’s an ill-kept secret that basically everyone in academia is a specialist. Nobody is just a “physicist”, or just a “high energy theorist”, or even just a “string theorist”. Even when I describe myself as something as specific as an “amplitudeologist”, I’m still over-generalizing: there’s a lot of amplitudes work out there that I would be hard-pressed to understand, and even harder-pressed to reproduce.

In the end, each of us is only going to understand a small subset of the vastness of our subject. This is problematic when it comes to attending talks.

Rarely, we get to attend talks about something we completely understand. Generally, we’re the ones giving those talks. The rest of the time, even at conferences for people of our particular specialty, we’re going to miss some fraction of the content, either because we don’t understand it or because we don’t find it interesting.

The question then becomes, why attend the talk in the first place? Why spend an hour of your time when you’re not getting an hour’s worth of content?

There are a couple reasons, of varying levels of plausibility.

One is that it’s always nice to know what other subfields are doing. It lets one feel connected to one’s compatriots, and it helps one navigate one’s career. That said, it’s unclear whether going to talks is really the best way of doing this. If you just want to know what other people are doing, you can always just watch to see what they publish. That doesn’t take an hour, unless you’re really dedicated to wasting time.

A more important benefit is increasing levels of familiarity. These days, I can productively pay attention to the first quarter of a talk, half if it’s particularly good. When I first got to grad school, I’d probably tune out after the first five minutes. The more talks you see on a subject, the more of the talk makes sense, and the more you get out of it. That’s part of why even fairly specialized people who are further along in their careers can talk on a wide range of subjects: often, they’ve intentionally kept themselves aware of what’s going on in other subfields, going to talks, reading papers, and engaging in conversation. This is a valuable end goal, since there is some truth to the hype about the benefits of interdisciplinarity in providing unconventional solutions to problems. That said, this is a gradual process. The benefit of one individual talk is tiny, and it doesn’t seem worth an hour of time. Much like exercise, it’s the habit that provides the benefit, not any individual session.

So in the end, talks are almost always unsatisfying. But we keep going to them, because they make us better scientists.

You get paid to learn. How bad can that be?

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In my “who am I” post, I describe being a grad student as like being an apprentice. I’d like to elaborate on that.

Ph.D. programs in the sciences are different at every school, but they have a few basic features. Generally you enter them with a bachelor’s degree from another university. The program lasts for somewhere between four and six years, longer for particularly unfortunate cases. Sometimes you get a Master’s degree after the first two years, sometimes you don’t, but you don’t usually have to get it from another school. Generally the first two years mostly involve taking courses while the later years are mostly research, but this can vary as well. And in general, once you’re in the program, you get paid: either as a Teaching Assistant, in which case you help grade papers, lead lab sections, and sometimes give lectures, or as a Research Assistant, in which you are paid to do research.

This last is occasionally confusing to people. If a Ph.D. student learns by doing research, then why are they also paid to do research? That sounds like not just getting your education for free, but being paid for it, which sounds at the very least like a very good deal.

There are two ways to think about the situation. One, as I mentioned in my “who am I” post, is as an apprenticeship. An apprentice is expected to learn on the job, and provided they learn enough they are eventually certified to work on their own. Despite this, an apprenticeship is still very much a job. An apprentice is subservient to their master, and can generally be counted upon to work on the master’s projects and help the master in their job. In much the same way, a Ph.D. student is not certified to work on their own until they graduate from the program and obtain their Ph.D. In the meantime they are subservient to their advisor, and they have to take their advisor’s desires into account when choosing research projects. In general, most of a grad student’s research projects will be part of their advisor’s research in one way or another, furthering their advisor’s goals. Beyond the research itself, grad students will often have other duties, depending on the nature of their advisor’s work, especially if their advisor has a lab with complicated equipment that needs to be maintained.

The other thing to realize is that grad students are, ostensibly, part-time workers. The university pays me for 20 hours a week of work. The thing is, though, I don’t just work part-time. I work full-time. I also work at home, on the weekends…whenever I can make progress on my research (and I’m not doing some side project like this blog or taking a needed sanity break), I work. So if I work 40 hours a week and am paid for 20, that means I am effectively spending half my income on education.

Not so free, is it?

It’s not as if any of us could just work less and take on another part-time job, either. Apart from the fact that many grad students are international students on visas that don’t allow them to get other jobs, it is research itself: keeping up, making progress, working towards graduating, that takes up so much of our time. To get any education out of the process at all, we have to be involved as much as possible. So we are, inevitably, paying for our education. And hopefully, we’re getting something out of it.