The relationship between free-spirited Sofi (Astrid Bergès-Frisbey) and Ian (Michael Pitt) comes to a gruesome end in “I Origins.” (Fox Searchlight)

The thesis of Mike Cahill’s new film “I Origins” — that reincarnated souls can be identified through iris biometrics, or high-tech eye scans — is certainly no more outlandish than the premise of “Another Earth,” Cahill’s 2011 entry into the world of sci-fi philosophizing. The filmmaker’s narrative-film debut, which he wrote with fellow Georgetown University graduate Brit Marling, postulated the existence of a parallel world just a short rocket trip away, and was as notable for its physical impossibility as for its intriguing existential implications.

But where “Another Earth” could be read as a giant metaphor for second chances, “I Origins” is a more straightforward thriller, the sort that can’t really be digested without swallowing its suppositions whole. What prevents them from landing in your stomach with a thud is the fact that its protagonists — a married couple played by Michael Pitt and Marling — are scientists who find the eye theory, at least initially, a load of hogwash.

The fact that their skepticism mirrors ours helps immensely.

Pitt and Marling play Ian and Karen, eye researchers who accidentally discover, via a global database of eye scans, that there’s a child in India, played by newcomer Kashish, whose eyes exactly match those of a former girlfriend of Ian’s, a free spirit named Sofi (Astrid Bergès-Frisbey).

Much of the film’s first half is devoted to Sofi, who is killed in a freak — and unnecessarily gruesome — elevator accident on their wedding day. Yet even if Sofi hadn’t died, Ian later notes, their relationship was probably doomed. Sofi believed in a world of spirits, and Ian trusts only what he can see with his eyes. Like her husband, Karen is an empiricist. But when this eye-scan anomaly crops up, Karen encourages Ian to fly to India and investigate.

What he finds there is a mystery both open-ended and suggestive. The girl, Salomina, does indeed have Sofi’s eyes, which were an otherworldly combination of blue, hazel and other stray flecks of color. What seems, on one level, pure — if unlikely — coincidence, eventually gathers more weighty overtones when Ian tests Salomina with a game of pictorial association meant to determine whether she has, in some part of her unconscious mind, memories of a former life.

The film ends with an ambiguous, yet powerful conclusion. It doesn’t answer the question it raises, yet the way it’s asked keeps it echoing in your head.

Except that Cahill can’t seem to leave well enough alone. What follows that perfectly good — even perfectly beautiful — ending is a post-credits sequence that comes close to ruining the delicious uncertainty left hanging in the air. It’s the kind self-sabotage that has, oddly enough, become a hallmark of his films with Marling, who also starred in and produced “Another Earth.”

It’s not just Cahill. Marling also frequently collaborates with Zal Batmanglij, another Georgetown alum, whose film projects with her include “Sound of My Voice” and “The East.” To some degree, the problem with all four of these films (the last two of which deal with time travel and violent eco-radicalism) is the same. All too often, they begin in an intriguing direction but then run off the rails. They’re like late-night, dorm-room conversations that get taken too far when one of the participants — possibly fueled by a mind-altering substance — starts insisting that he or she has all the answers, when all that’s really needed is to ask the right questions.

★ ★ ½

R. At area theaters. Contains obscenity, nudity and sensuality. 113 minutes.