This little book contains the course that I had the pleasure of giving at the 8th Estonian Winter School in Computer Science (EWSCS ’03) held at the beautiful Palmse manor in Lahemaa National Park, Estonia, from March 2nd through 7th, 2003. There I gave four 90-minute lectures on algorithmic information theory (AIT), which is the theory of programsize complexity. Each of these lectures is one chapter of this book.
In these lectures I discuss philosophical applications of AIT, not practical applications. Indeed, I believe AIT has no practical applications.