This is a quote by Richard Feynmann. I really like it. It is easy to just say I understand something, but if you can make something from scratch, and it works, then at some level you really must understand it. I was reminded of it when I started on some course notes for a course I am teaching this autumn. It is on biological physics, so I will be talking about applying physics to life. Living things are very complex, and so we don’t truly understand a lot of how they (and we work). We certainly can’t create a human body from scratch in the lab. There is no Dr Frankenstein.

Over the last 15 years we have, however, learnt how to do a bit of programming of bacteria, to make them flash in synchrony.

The bacteria have had two simple circuits engineered into them. These circuits can do functions similar to the electric circuits in computers, washing machines etc., but they are not made of wires, but of genes and proteins. One of these circuits makes the bacteria flash periodically, i.e., fluoresce brightly, then go dark, fluoresce again, etc. The other synchronises the flashes of the large numbers of bacteria together. The video is of huge numbers of bacteria that are too small for individual bacteria to be seen.

I will be teaching a model of a simple switch which is part of the circuit that makes the cells flash. We understand this circuit, we can create it. With a bit of luck, if my notes are OK, the students might too.