According to Bill Roeder in Newsweek in 1978: "Thomas Pynchon, the reclusive author whose last book was "Gravity's Rainbow" in 1973, has two novels in the works. One is said to be a science-fiction thriller inspired by Pynchon's passion for "Mothra" and other Japanese horror movies. The other book involves the Mason-Dixon line, and Pynchon is now in England looking into the lives of Charles Mason and Jeremiah Dixon, the British surveyors who established the Pennsylvania-Maryland boundary in the eighteenth century. As part of his previous research, Pynchon walked the 233-mile length of the Mason-Dixon line." 
Instead, his first publication after Gravity's Rainbow was a collection of stories - containing a mystifying introduction by Pynchon.
Excerpts from Criticism
"If Pynchon took the title Slow Learner from 1984, and if "Introduction" is a confession or revisionist autobiography, its logic is characterized by the post-torture forgetfulnes, non sequiturs and other logical fallacies Winston Smith experiences and learns not to question. [...] Similarly, in "Introduction" —what we might call Pynchon's secret reintegration— Pynchon makes some rather startling comments on his own writing which, on close reading, are either questionable or very doubtful. Of "Entropy" he says, "because the story has been anthologized a couple-three times, people think I know more about the subject than I really do" (12) Such cause-and-effect logic suggest that the more the story is anthologized, the more people will think Pynchon knows about entropy, and conversely, the less the story is anthologized, the less people will think Pynchon knows about entropy. This self-deprecating statement not only parodies Tony Tanner's remark about The Crying of Lot 49 —"The more we think we know, the less we know we know" (56)— but also becomes itself an entropic formula reconfigured —more or less— as proportional relations concerned with anthologization, population, information and knowledge."
Quoted from: Terry Reilly. "A Couple-Three Bonzos: "Introduction," Slow Learner and 1984." Pynchon Notes 44-45, spring-fall 1999: 5-13 (8-9).
- Bill Roeder. "After the Rainbow: Bill Roeder with Bureau Reports." Newsweek (United States edition), August 7, 1978, Section Periscope: 17.
- Terry Reilly refers in this quote to: Thomas Pynchon. "Introduction." Slow Learner, Little, Brown, Boston, 1984, and cites from Tony Tanner. Thomas Pynchon. Methuen, London, 1982.