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Documentarian Roger Nygard investigated the mindset of “Star Trek” true believers in “Trekkies” and “Trekkies 2,” and now he casts his net more widely in this film, which strings together excerpts of interviews he conducted with people of widely divergent backgrounds and faith systems (or in some cases, non-faith systems) on the “big issues” of reality and religion.

The breadth of coverage is impressive; those included range from arch-atheist Richard Dawkins on the one side to fire-and-brimstone campus preacher Jed Smock on the other. But while scientists and religious figures get their say, so too do performers like Julia Sweeney, movie directors like Irvin Kershner and just regular folk, including a young acquaintance of Nygard’s, one Chloe Revery, who dismisses the afterlife as bunk with absolute certitude.

Throughout Nygard maintains a cheerfully accommodating attitude, playing a Michael Moore figure without the better-known man’s anger (or bulk). He’s relentlessly good-natured, refusing to react with scorn at even the most absurd statements (and maintaining a bemused air even in a “Roger & Me” moment when he tries unsuccessfully to get access to Pope Benedict XVI). He does, however, set up a sort of mini-debate between Smock and chum Stevie Ray Fromstein, a session that resembles the Drummond-Brady courtroom confrontation from “Inherit the Wind.” But even it is conducted without rancor. And most of the interviewees respond in kind, though a few get a mite hot at times.

The Smock-Fromstein exchange is also one of the longest segments in the film (apart from an excursus on Dallas’ Cathedral of Hope), which is edited mostly in quick cuts designed to set off opposing viewpoints. The technique keeps the viewer on his toes (and since the interlocutors are generally enjoyable types, amused), but it also makes you wish that some speakers might be heard at greater length.

It also means that in the final analysis “The Nature of Existence” doesn’t dig very deep, and anyone looking for it to provide answers will be severely disappointed. But it’s a journey that prizes intellectual search over simplistic solutions, and if you come to it with a similar attitude you should enjoy ambling along with Nygard as he tours the world and engages almost anyone willing to talk to him, from Druids to New Age swamis, in conversation about what “here” is and why we’re in it.