Do theorists dream of thought experiments?

2nd May 2018
two men look at a laptop in front of a chalkboard wall with the words heroes of physics in comic font nearby

I was born and raised in sunny and beautiful Barcelona, where I graduated in physics in 2002 followed by a Ph.D. thesis in theoretical particle physics four years later. And for better or for worse, I have been a particle theorist ever since. In this first blog post, I will try to tell you a bit about how theoretical physicists spend their time (yes, the big question everyone has been asking themselves since the beginning of time!)


Indeed, one of the most awkward questions that scientists must endure in family gatherings and other related social events is about what exactly we do for a living. At least my experimental colleagues can reply by explaining that they do experiments, tinker with big detectors and that they basically measure things. But a theorist? Do we spend all our time just idly sitting around and ``theorizing''? What does that even mean? And do we get paid for that? Sometimes, if I aim for a short conversation, I simply reply to these questions that ``I teach at the university'', which however often leads to the follow-up remark about what we do when we are not teaching...

The answer to these questions, like many other things in life, is a bit more complicated than that.

One of my favorite anecdotes in this context is the one where one of my postdocs was asked by his parents about what he was currently working on. He replied by saying that the LHC had recently discovered a new particle, the Higgs boson (so far so good) and that now we were busy trying to find two Higgs bosons. For the interested reader, the project studied the feasibility of measuring Higgs pair production at the LHC, an extremely challenging analysis due to the low signal rates. Apparently, his parents stared back at him with a mixture of admiration (do you really get paid for doing that?) and of suspicion (all those years studying and then ending up doing something so silly?). It is indeed not easy for us to explain what we do for a living, let me try to have a go at providing a better answer.

So, what does a theorist do when no one is looking? First of all, I will state the obvious: there is no template for a particle theorist, in exactly the same way that there is no template for a scientist: there is an infinite number of ways to live the scientific adventure, each one completely different from the rest.  Therefore, I will try to tell you how I spend most of my days, without any pretense of generalization to my peers.

My day typically starts with one of the most sacred and venerable activities of academic life: replying to emails. This exciting activity takes between one or two hours of my time (if I am lucky). I am always reminded of one of my former colleagues in Oxford, a prominent string theorist, who was often approached by schools suggesting a shadowing scheme, where a student was supposed to follow him all day to feel what it was like to be a scientist. But my colleague always rejected such offers, with the sound excuse that seeing him spending his days answering (mostly bureaucratic) emails was not the most stimulating activity for a young mind! So, apologies if I just broke your ideal image of an Einstein-like physicist, idly wandering in some beautiful forest with her mind busy constructing the next theory of gravity, but this is the crude reality.

Another big chunk of my time is spent in teaching activities. As opposed to common lore, teaching takes much more time than the nominal presence of the professor in the classroom. It also involves preparation, writing lecture notes, assignments, marking, contact hours etc. For example, I always prepare lecture notes so that the students can complement their own class notes. This is a lot of work but in the long term it pays off, and if you are lucky you can even try to turn lecture notes into textbooks (for the pride of it, certainly not for the money).

While most physicists I know enjoy teaching, the main challenge here is to balance the time invested in teaching with research and management activities, such as applying for grants and sitting in committees. The problem is often made acuter, especially since universities and research institutes often offer conflicting incentives to academics, as aptly summarized by Jorge Cham's Ph.D. Comics: we are supposed to be outstanding researchers, model teachers, and accept all the service tasks that our department head kindly proposes to us. In real life, this boils down more to juggling than to any kind of rational organization.

pie charts of how professors spend their time divided: how they actually spend it vs how their dept wants them to and how they want to.

So, let's assume the highly improbable scenario that my inbox is completely empty and I have no teaching activities to carry out, no meetings to sit in on, no bureaucratic deadlines. Hooray! It is finally time to do some research! And what does that exactly entail? For instance, we recently published a study demonstrating the onset of a qualitatively new dynamical regime of Quantum Chromodynamics (the theory of the strong interaction), called BFKL effects. These effects have been looked at practically since the original formulation of QCD, forty years ago.  Therefore, we were very pleased to discover them from our analysis.


So how did we get there? Well, I started looking at this problem during my Ph.D. thesis (but had no time, so I dumped it on the pile of unfinished drafts). I resumed working on this project during my postdocs (again no time, so a slightly improved version of the draft went to the same pile). At last, in the last three years, together with some young and bright members of my group, we managed to put together the various pieces required for the analysis: the theoretical calculations, their implementation in computing programs, the data analysis, the statistical interpretation framework, and so on. So, in a nutshell, we have to combine a variety of expertise, from problem-solving to coding, from computing integrals to dissecting experimental measurements.

At each of these steps, we found endless pitfalls and problems, from the more pedestrian but still painful (the code returns garbage after the system manager has updated the compilers!) to the more conceptual ones (three people did this calculation independently and each of them got a different result!). But with enough patience and dedication, all these issues were overcome, and we ended up with a beautiful result which makes me very proud: unveiling new fundamental aspects of Nature is, after all, the very reason we became physicists!

All this is very nice and so on, but one also needs to be realistic when presenting how research works in practice. As you can imagine from the previous example, the daily life of a scientist in general, and of a particle theorist in particular, can be very dry: as Feynman used to say:

Theoretical research is basically a continuum of despair punctuated by short ecstatic moments of quasi-revelation once we find the solution of the problem that has tortured us for ages (and shortly afterwards, back to despair again).

From the practical point of view, research in theoretical particle physics owes a lot to the old but good method of sitting down and discussing together. As everyone familiar with the Big Bang Theory show knows, physicists love nothing more than discussing next to a blackboard, the bigger the better (size really does matter in this context).  For a physicist, especially for theorists, the ideal research institute would be one where all walls are covered with blackboards, there is high-speed internet in every corner, and a steady supply of coffee. We don't really need much more to thrive! As proof, I submit this image of two Nikhef theorists in their prime habitat.

two men look at a laptop in front of a chalkboard wall with the words heroes of physics in comic font nearby

Another activity that takes some of my time (though I wish it could take more!) is outreach and science popularization. There are many types of outreach (I will discuss social media in particular in a future blog post), let me just mention one: schools. Motivating young people to follow scientific careers is extremely important and, in my opinion, something that we scientists owe to society. Below you can see students from the Rotterdam International Secondary School on a recent visit to Nikhef. We had an amazing time together: they learned about particle physics and the Higgs boson, they built their own toy gravitational wave detector (a laser interferometer, no less!) and they visited the workshops where the future of particle physics is being built right now. A scientific career can be hard and challenging, but to me, the fascination and passion that those kids have are absolutely worth all our efforts.

teenaged students and professors standing in front of a chalkboard wall for a group photo
Nationaal Instituut voor Subatomaire Fysica