During the period in which he wrote Cryptonomicon, Stephenson read George Dyson's Darwin Amongst the Machines, which led him to Gottfried Leibniz's interest in a computing machine, the Leibniz–Newton feud, and Newton's work at the Royal Treasury. He considered this "striking when [he] was already working on a book about money and a book about computers," and became inspired to write about the period. Originally intended to be included in Cryptonomicon, Stephenson instead used the material as the foundation for Quicksilver, the first volume of the Baroque Cycle. The research for the sprawling historical novel created what Stephenson called "data management problems", and he resorted to a system of notebooks to record research, track characters, and find material during the writing process.
In Quicksilver, Stephenson places the ancestors of the Cryptonomicon's characters in Enlightenment Europe alongside a cast of historical individuals from Restoration England and the Enlightenment. Amongst the cast are some of the most prominent natural philosophers, mathematicians and scientists (Newton and Leibniz), and politicians (William of Orange and Nassau) of the age. In an interview, Stephenson explained he deliberately depicted both the historical and fictional characters as authentic representatives of historical classes of people, such as the Vagabonds as personified by Jack, and the Barbary slaves as personified by Eliza. In his research for the characters, he explored the major scholarship about the period.
Stephenson did extensive research on the Age of Enlightenment, noting that it is accessible for English speaking researchers because of the many well documented figures such as Leibniz, Newton and Samuel Pepys. In the course of his research he noted historiographic inconsistencies regarding characters of the period which he had to reconcile. Especially prominent was the deification of Newton, Locke and Boyle and their scientific method by Enlightenment and Victorian scholars. He considers the scientific work done during the Baroque period as crucial to the Enlightenment. From his research he concluded that the Enlightenment in general "is and should be a controversial event because although it led to the flourishing of the sciences and political liberties and a lot of good stuff like that, one can also argue that it played a role in the French Revolution and some of the negative events of the time as well." The portrayal of a confusing and uncertain era develops throughout the book.
Some reviewers commented that Stephenson seems to carry his understanding of the period a little too far at times, delving into too much detail. Nick Hasted of The Independent wrote that this research made "descriptions of Restoration London feel leaden, and intellectual discourses between Newton and his contemporaries textbook-dry." Despite the thorough examination of the period, however, Stephenson does take liberty in depicting the Enlightenment. Both main and secondary fictional characters become prominent members of society who advise the most important figures of the period and affect everything from politics to economics and science. For example, he repopulates the real Cabal Ministry with fictional characters.