ALTERNATE HISTORY -- the mix of "what if" and "if only" best exemplified by Philip K. Dick's The Man in the High Castle (in which the U.S. has lost World War II) and Ward Moore's Bring the Jubilee (which has the South winning the Civil War) -- is one of science fiction's more rigorous sub-genres. Few writers, however, attempt to give scientific or philosophical rationales to their alternative worlds, Dick's novel being something of an exception. Robert Anton Wilson, in his trilogy, Schrodinger's Cat, now completed with the publication of The Trick Top Hat and The Homing Pigeons (Pocket Books, $2.50 each) makes a bid to rectify alternative history's lack of explicit philosophical foundations.

Despite Wilson's rather disingenuous prefatory remark that the triloghy's books may be read in any order, they are in fact three parts of an extended novel, and The Universe Next Door (Pocket Books, $2.50) -- published in 1979 -- is best read first (indeed, all three books must be read to make any sense of this quirky novel). Here the reader is introduced to the Wheeler-Everett-Graham model which holds that anything that can happen does happen, each happening forming, as a consequence, its own selfconsistent universe "next door" in superspace.

All the major characters of the triology are also first seen in The Universe Next Door: Dr. Frank Dashwood of Orgasm Research, obsessed with quantifying all aspects of human sexuality; the mad dwarf, Markoff Chaney, enemy of Dashwood and all those who would quantify any aspect of reality; Marvin Gardens, the cocaine-snorting Norman Mailer clone who is convinced that extraterrestrials have taken over everything (especially publishing); Dr. Blake Williams, distinguished neuropsychologist, specializing in primates (i.e., homo sapiens); Furbish Lousewart V, the Ralph Naderesque President of Unistat; Justin Case (an example of the puns committed throughout the trilogy), a post-literate film critic; terrorists of every stripe, intelligence agents, porno actresses, and transvestites, all of whom undergo shifts in role, name, or world-view as they find themselves in each alternate universe. There is even a character named Joe Malik (first seen in Wilson and Robert Shea's Illuminatus series), who retires from editing a magazine to write a novel about a man named Robert Anton Wilson who is writing a comedy about quantum physics called Schrodinger's Cat.

In The Trick Top Hat, which follows the sexual and paranoid adventures of these many characters in a vaguely familiar world, Wilson's narrative becomes frantically madcap as he bombards the reader with puns, jingles, snatches of pseudo-Joycean rhetoric (much of which seems thrown in for pyrotechnic's sake), and some extended passages of brilliant satire.

The "form" of this volume, as Wilson tells us in an appendix titled "A Guide for the Perplexed," is Bell's Theorem, which holds that any two particles once in contact will continue to influence each other, no matter how far apart they may go -- a violation of light's universal speed limit. Wilson labors hard to dramatize this theory -- Dr. Blake Williams lectures throughout the narrative on its implications -- and we see various characters influencing each other in "impossible" ways, but the effort, although it pays satirical dividends, does not succeed in forging a structure for the book.

The Joycean narrative of The Trick Top Hat grows increasingly manic and disjointed in The Homing Pigeons, where Wilson continues to touch on everything from metaphysics and social history to love and man's destiny. He makes yet another attempt to jam the story into a Procrustean quantum model -- in this case, Dr. John A. Wheeler's "non-objectivity" alternative to Bell's Theorem -- but it seems a half-hearted effort.

We are left with a cacophony of puns, in-jokes, kinky sex, and sometimes hilarious, paranoid set pieces. What is not provided is a denouement that convincingly ties the disparate elements of the trilogy together. Instead, the work flies apart like galaxies speeding away from earth at light speed. We are left only with Wilson's optimistic eschatology: "great golden ships sailing . . . into the center of the galazy . . . And the ships, like homing pigeons, were going back where the experiment began, out of space, out of time." The reader is led to expect much more than is delivered by the exuberance and self-proclaimed ambition of Schrodinger's Cat.

In The Affirmation (Scribners, $10.95), Christopher Priest uses parallel worlds to illuminate a man's descent into madness.

Peter Sinclair's father dies, his job is terminated, and his lover, Gracia, leaves him. Living in an isolated cottage, he attempts to find meaning by writing his life story.

His efforts lead nowhere until Peter invents a fictional persona who lives in the imaginary city of Jethra. This parallel world promises to heal him, and he writes about it obsessively, rapidly losing touch with the world he had assumed to be real.

From this point chapters alternate Peter's "real," alienated world with the imaginary Peter's Jethran reality where he has a won an immortality treatment as a lottery prize. Journeying through a sub-tropical paradise called the Dream Archipelago to claim it, he meets Seri, the counterpart of his lost lover. Together they roam through the islands while Peter agaonizes over whether to accept the treatment.

In Peter's other world, he confronts his disintegration. He seeks a reconciliation with Gracia, but she attempts suicide. Peter suspects that he may have driven her to it. The worlds shift, and Peter finds himself back in the healing climes of the Archipelago. There he undergoes the treatment, only to lose his memory as a side effect. Seri, using a parallel manuscript which this alternate Peter has written about himself, attempts to rebuild his personality. She succeeds only in giving him a fabrication of himself, based on her interpretation of a manuscript which has Peter living in "London" with a lover named "Gracia."

Left with this second-hand identity, Peter finds his two worlds intermingling, he inhabits both at once and can find his true self nowhere. Finally, Peter's manuscript and Priets's novel fuse, looping back upon themselves in the book's startling conclusion.

The Affirmation is that rarity: a novel about madness that clarifies the experience rather than reducing it to a jumble of sensation. Reading this book, you must be careful. The Archipelago is seductive; you might want to journey there forever.