"What do you do?"

(As published on iopblog)

Physics has always been my vocation. Perhaps it’s because my dad is an engineer, so my earliest memories are of soldering irons, microscopes and torque gauges. For whatever reason, I have always cared very deeply about trying to understand how the world works, and have never lost the childish impulse to ask “why” on every possible occasion. I pursued physics, and am now lucky enough to do it for a living. So when someone asks me “What do you do?” you might expect me to have a good answer at the ready.

It’s a question we all get asked whenever we meet someone, whether at a party, a bus-stop or (so we are led to believe) an audience with the Queen. Unless your life conforms to some standard set of labels, you probably find the question as tricky to answer as I do. You could just give your job title, but that doesn’t really summarise you, does it?

“I’m a university lecturer,” I’ll say.

I could have told them I’m a physicist, teaching and researching at Leeds University Department of Applied Maths, or that I’m a proud father – the activities that occupy most of my time. But I usually go with the job title. This prompts the response,

“What’s your subject?”

As any physicists out there will know, the traditional course of this conversation goes as follows:

“Physics.”

“Oh, I wasn’t any good at physics at school,” …followed by an uncomfortable silence.

I never know how to respond to that. “Oh dear” just sounds patronising, and “I was” would be worse. I would be grateful to hear your suggestions for diverting this social train-crash.

But ever since physics celebs Brian Cox and (fellow physicsfocus blogger) Jim Al-Khalili have captured the public imagination, I am pleased to report that the conversation these days tends to run more like this:

“Physics”

“Oh, that’s really interesting. What do you work on? Is it astronomy or subatomic particles?”

Of course, like anyone with properly functioning goose-pimples, I am filled with fascinated awe by both the vast and tiny extremes of our universe. But my own research is in a less well-publicised area of fundamental physics: statistical mechanics.

Statistical mechanics is the third pillar which, together with General Relativity and Quantum Mechanics, underpins our understanding of the physical world. Stat mech, as it’s known to its friends, lies between the realms of the very large and the very small, linking the two. It is the theory that explains why ice is hard and water is runny and liquid-crystals are weird.

Often the next question I am asked is:

“So, what substance are you working on at the moment?”

This is the point at which my interlocutor might reasonably begin to lose patience. I would love to be able to give a straight answer to that question, as a chemist or an engineer or even many physicists could.

“It’s not like that,” I have to say.

You see, some types of research apply to specific substances or specific gadgets. Some scientists study graphene, for instance, and some technologists design solar cells. But often, it’s more useful to classify research by the ideas that it addresses, rather than its applications.

Stat mech describes what happens when vast numbers of tiny particles interact with each other to form large-scale materials. Its principles can be applied equally well to water molecules, electrons in a metal, or the neutrons in a pulsar, to predict their behaviour en masse. The only proviso is that the collection of particles must be at equilibrium, meaning that they are not flowing.

Image: This artist’s concept shows young, blue stars encircling a supermassive black hole at the core of a spiral galaxy like the Milky Way. Credit: NASA, ESA, and A. Schaller (for STScI)

In my research, I am working to extend the well-established theory, to find the principles governing non-equilibrium systems, ie collections of objects that are in a state of flux, whether they are molecules of molten plastic flowing into a mould, or stars swirling round a black hole. I study the universal principles behind these types of collective motion, rather than focussing on a particular case. Any progress that can be made in this area will have countless applications that haven’t been imagined yet, so it’s a worthwhile thing to do, as well as being fascinating.

I believe that we need both types of research – ideas-based and applications-based – in order to achieve a really broad, deep and productive understanding of the physical world. I know which type I personally find more interesting. Unfortunately, it’s the one that’s hardest to explain at parties. It’s probably a blessing that I’ve never met the queen – I’m not sure she’s got the stamina for it.