Fresh from doing two Open Day talks last week I thought I’d write a few words here about something that cropped up in the question-and-answer session.

For a start, I should explain that here at Maynooth University there are two Physics departments, one the Department of Theoretical Physics (of which I am a Faculty member) and the other the Department of Experimental Physics. These two units are in the same building but are largely separate in terms of teaching and research.

For instance, when students enter on our General Science degree programme they have to choose four subjects in the first year, including Mathematics (much as I did when I did my Natural Sciences degree at Cambridge back in the day). Picking `double physics’ (i.e. Experimental Physics and Theoretical Physics) uses up two of those choices, whereas Physics was a single choice in the first year of my degree.

To confuse matters still further, the Department of Theoretical Physics only recently changed its name from the Department of Mathematical Physics and some of our documentation still carries that title. I got asked several times at the weekend what’s the difference between Theoretical Physics and Mathematical Physics?

As far as Maynooth is concerned we basically use those terms interchangeably and, although it might appear a little confusing at first, having both terms scattered around our webpages means that Google searches for both `Mathematical Physics’ and `Theoretical Physics’ will find us.

It’s interesting though that Wikipedia has different pages for Mathematical Physics and Theoretical Physics. The former begins

Mathematical physics refers to the development of mathematical methods for application to problems in physics. The Journal of Mathematical Physics defines the field as “the application of mathematics to problems in physics and the development of mathematical methods suitable for such applications and for the formulation of physical theories”. It is a branch of applied mathematics, but deals with physical problems.

while the latter starts

Theoretical physics is a branch of physics that employs mathematical models and abstractions of physical objects and systems to rationalize, explain and predict natural phenomena. This is in contrast to experimental physics, which uses experimental tools to probe these phenomena.

The difference is subtle,and there is obviously a huge amount in common between these two definitions, but it is perhaps that Theoretical Physics is more focused on the use of mathematics to account for the results of experiment and observations whereas Mathematical Physics concerns itself more with the development of the necessary mathematical techniques, but I’m sure there will be readers of this blog who disagree with this interpretation.

For the record here is what Wikipedia says about Experimental Physics:

Experimental physics is the category of disciplines and sub-disciplines in the field of physics that are concerned with the observation of physical phenomena and experiments. Methods vary from discipline to discipline, from simple experiments and observations, such as the Cavendish experiment, to more complicated ones, such as the Large Hadron Collider.

I’d say that theoretical physicists are more likely than mathematical physicists to be working closely with experimentalists. I count myself as a theoretical physicist (that’s what I did in Part II at Cambridge, anyway) though I do work a lot with data.

Anyway, as an experiment, I asked the audience at my Open Day talks if they could name a famous physicist. Most popular among the responses were the names you would have guessed: Einstein, Hawking, Feynman, Dirac, Newton, Schrodinger, and some less familiar names such as Leonard Susskind and Brian Greene. Every single one of these is (or was) a theorist of some kind. This is confirmed by the fact that many potential students mention similar names in the personal statements they write in support of their university applications. For better or worse, it seems that to many potential students Physics largely means Theoretical (or Mathematical) Physics.

Although it is probably good for our recruitment that there are so many high-profile theoretical physicists, it probably says more about how little the general public knows about what physics actually is and how it really works. For me the important thing is the interplay between theory and experiment (or observation), as it is in that aspect where the whole exceeds the sum of the parts.

It might seem a bit strange to have two Physics departments in one University – though it seems to work alright in Cambridge! – but I think it works pretty well. The one problem is that there isn’t a clear entry point for `Physics’ without an adjective. Students can carry Theoretical Physics and Experimental Physics through all the way to final year and get a joint honours degree (50% theory and 50% experiment) or they can pick one to do single honours, but we might attract a few more students if the former possibility were just called `Physics’. Perhaps.