Does this question sound familiar? Regular readers may remember a story we posted in June of 2007 about a project by researchers Shane Legg and Marcus Hutter to answer this question. In June they published a paper (PDF format) containing a large collection of definitions of intelligence from various fields. After six months of study, they've extracted the essential features common to all these definitions and created a mathematically formal definition of machine intelligence that can be applied to arbitrary machines. Their new new paper is titled, "Universal Intelligence: A Definition of Machine Intelligence" (PDF format). In addition to providing what they believe to be an equation that "captures the concept of machine intelligence in the broadest reasonable sense", they also show how their definition is related to the theory of universal optimal learning agents.