Ray Solomonoff, the father of algorithmic probability theory and one of the founding fathers of Artificial Intelligence, died December 7th after a brief illness.

Solomonoff was a pioneer of probabilistic thinking in AI, and in general. It is my own view that the value of probabilistic thinking is the single most important insight about reality that humanity has ever had, and Solomonoff helped add to that great edifice with his idea of Algorithmic Probability.

Solomonoff was the founder of universal inductive inference, which gives a mathematically optimal method of predicting the next bit of sensory information in a sequence based on prior information. (Unfortunately, it is incomputable, though computable approximations have been used throughout the field of AI.) As far as I know, Solomonoff made the first mathematically rigorous attempt at automated sequence prediction.

Solomonoff’s work is being carried forward by theorists such as Marcus Hutter, Juergen Schmidhuber, and Shane Legg, among many others.

Just last week I posted on AIXI, which is essentially a marriage between Solomonoff’s universal inductive inference and decision theory. Inductive inference tells you what is going to happen next, while decision theory tells you what to do next. Put these together and you get a model for AI.

Solomonoff kept publishing and engaging with the AI community right up until his death. It seems very likely that, if and when strong AI is created, the designer will owe a great debt to Solomonoff’s work. Let’s honor his memory by becoming more familiar with his achievements and making sure that his ideas stay alive.