''I love reading novels,'' says a character about midway through Neal Stephenson's 900-plus-page, pixilated picaresque Quicksilver. ''You can understand them without thinking too much.'' This is Stephenson's little joke, a verbal spike buried deep in this warm, loamy novel of ideas, adventure, science, and politics. Are you put off by the notion of plowing through a post-cyberpunk's expansive book about the 17th and 18th centuries, with such real-life figures as scientist-dreamer Sir Isaac Newton and diarist Samuel Pepys commingling with fictional characters like Jack Shaftoe, a London urchin who grows up to be a world-traveling womanizer, and Eliza, a former slave to whom Jack shows the world? So was I.
But the great trick of ''Quicksilver'' is that it makes you ponder concepts and theories you initially think you'll never understand, and its greatest pleasure is that Stephenson is such an enthralling explainer. Alchemy, the I Ching, ''cryptikal'' codes, and the origins of the stock market -- Stephenson's motley crew debates and illuminates these elements and many more. He throws in lots of sex, violence, and puns that are ''funny in a painful way'' -- his appetite for vulgarity is fully equal to his voracious learnedness. All of this enlivens transatlantic voyages of piratical mayhem, ribald plays like ''Once More Into the Breeches'' (the author provides the scripts, of course), and intellectual collisions between members of the real-life Royal Society over ''Natural Philosophy'' (i.e., science) so heated they make ''Crossfire'' sound like ''Sesame Street.''
Stephenson attracted a cult following with his sleek 1992 L.A. sci-fi novel ''Snow Crash,'' and his audience has grown to best-seller-size proportions. Longtime fans will be rewarded in combing ''Quicksilver'' for references to his previous novel, 1999's hefty, exhilarating ''Cryptonomicon,'' with at least one character and numerous themes in common. But you don't have to read that big book as a prelude to this big book. ''Quicksilver'' may remind baby boomers of John Barth's 1960 countercultural bodice ripper ''The Sot-Weed Factor'' or name-your-favorite Thomas Pynchon. But as befits a novel that prides itself on its contradictions, in which magic is as real and important as science, comparisons are both apt and irrelevant.
''Quicksilver'' is just the first part of a trilogy collectively titled ''The Baroque Cycle.'' (The other two, ''The Confusion'' and ''The System of the World,'' are scheduled to be released in six-month intervals.) Stephenson has set himself up as the Lord of the Baroque, and he's going for broke -- risking possible exhaustion of imagination, or a conclusion that fails to tie up all the plot strands he's introduced; it's an immense task. Fortunately, he doesn't seem to view his massive project this way: He's having fun summing up, as one character puts it, ''all human knowledge... To write it down in a vast Encyclopedia that will be a sort of machine, not only for finding old knowledge but for making new...'' Stephenson's new machine is a wonderment to behold.