Looking at his biography on Wikipedia, it seems that he: 1. Earned a BS in Physics from Harvard with a near-perfect GPA. 2. Got into a PhD in Physics program.

Looking at his biography on Wikipedia, it seems that he: 1. Earned a BS in Physics from Harvard with a near-perfect GPA. 2. Got into a PhD in Physics program. 3. Dropped out of the Physics program to pursue a non-degree-track research program in AI. 4. Published stuff and gave talks. His work around that time sounds like what a typical grad student would be doing, i.e. performing research as a research assistant to a principal investigator: > While working (starting in 1975) as a research assistant at MIT under Gerry Sussman,[13] Stallman published a paper (with Sussman) in 1977 on an AI truth maintenance system, called dependency-directed backtracking.[17] This paper was an early work on the problem of intelligent backtracking in constraint satisfaction problems. As of 2009, the technique Stallman and Sussman introduced is still the most general and powerful form of intelligent backtracking.[18] The technique of constraint recording, wherein partial results of a search are recorded for later reuse, was also introduced in this paper.[18] Without looking into precisely what he did, that sounds like the sorta thing someone could type up as a dissertation and defend to earn a PhD.