# Au revoir les theories, Bonjour l’action

I am reading a biography of Pierre-Gilles de Gennes, by Laurence Plévert. De Gennes won the Nobel prize in physics in 1991. I guess he is a scientific hero of mine. The Nobel prize was for his work on understanding polymers and liquid crystals. You are probably reading this screen with a liquid crystal display of some sort (often called just LCDs). He perhaps contributed more to understanding what liquid crystals are, than anyone else.

Reading the biography, I am conscious of how much he has influenced me. I did meet him a couple of times but never talked science with him, but his scientific papers and a book he wrote inspired me. It has also affected how I teach. De Gennes’ style was often to use simple physical arguments to obtain estimates of the order of magnitude of a physical property, as opposed to grinding through heavy maths to try and obtain a very accurate answer.

In one of this semester’s biological physics lectures, I took the students through simple geometric arguments for how as the size of an animal increases, the mass increases as size cubed, whilethe weight-bearing capacity of the bones increases more slowly, as height squared. The faster increase of mass limits the size of animals. It is why there are no 50 m giants around.

When I wrote the lecture, I was not thinking about why I was trying to explain a physical phenomenon using simple estimates of how the important physical quantities scale, in this case with animal size. I just thought the students might be interested in the fact that you can use a bit of physics, and some GCSE maths, to show why there are no 50 m tall elephants wandering around africa. I hope they were.

So, at the time, they didn’t know why, and I didn’t think about why the lecture was in this style. But I guess  the lecture was in the style of de Gennes, so although he sadly died 5 years ago, his influence is still being felt. Who knows, maybe one the students will go on to do some teaching or lecturing of their own, and they make take some inspiration from how I teach.