Editorial

摘要

Yes, I know, don't give up the day job! Anyway, pick a word from the first line of the limerick. Now count the number of letters it contains and progress that number of words. For example, 'Einstein' contains eight letters and maps onto 'He'. Repeat this process to the end of the limerick and I guarantee... [drum roll]... that you will end up on the word 'divine'. This exercise seems to demonstrate the convergence of a Markov chain, though we can do better than that. Wherever you started, you selected the word 'light' en route and this is my theme for this issue of Mathematics Today. The United Nations has declared 2015 to be the International Year of Light and Light-based Technologies (IYL), and with very good reason. This year celebrates several anniversaries of events that changed our perceptions of light significantly.