(UNDATED) When neuroscientist and author David Eagleman described himself as a “Possibilian” during a National Public Radio interview earlier this year, he said he thought he was the only one.

But now, fans of his new book “Sum: Forty Tales From the Afterlives” are flocking to his so-called movement, forming online communities that forge a new middle ground between belief and unbelief.

“It’s not being an agnostic, which I find to be a weak term,” explained Eagleman, 38, a professor at Baylor College of Medicine in Houston. “Agnosticism is not knowing whether the guy with the beard in the cloud is real or not. “Possibilianism’ is going out and making up a bunch of new stories, because we know so much more now than those people who came up with those stories thousands of years ago.”

In contrast to traditional religious descriptions of heaven, hell, reincarnation and the like, the inventive scenarios in “Sum” range from afterlives that resemble airport lounges to failed utopian experiments. In one vignette, humans who die simply resume their laborious jobs maintaining the cosmos (Earth, it seems, was a rare vacation); in another, they end up in a somewhat mundane eternity, joined only by those they had met while alive.

In the possibilities that include a creator, he (or she) is generally frustrated, despairing or indifferent.

Raised a secular Jew, Eagleman said he dabbled in atheism as a young scientist before concluding that claiming any kind of certainty about what happens after we die — whether based on faith or science –was ultimately illogical.

“Sum,” which is being published in 16 languages, has become especially popular with Unitarians, mainline Protestants and liberal Jews, at least based on his speaking engagements and readers who approach him at signings, he said.

His newfound disciples include John Veneruso, 44, an engineer who lives in Portland, Ore. Raised a Catholic but now just an occasional Unitarian, Veneruso formed a “Possibilian” Facebook group after Eagleman’s NPR interview struck a chord during his commute.

“A number of my friends and I had tossed around these ideas for quite a while; even my mother and I had talked about this stuff over the years,” he said, adding that he has invented his own afterlife stories over the years with his three children, now ages 10 to 15. “I just didn’t have a name for it.”

In Veneruso’s experience, similar to other accounts shared in online Possibilian groups, the journey from faith to uncertainty happened sometime around college, when young adults become exposed to more in-depth religious history — warts and all — along with new philosophies and beliefs.

“I had been brought up thinking that ethics and morals and religious teachings of the church should be consistent, and yet I was seeing inconsistency,” he said. “I didn’t believe they had a lock on the truth any more so than any other religion.”

While young adults have had similar revelations for generations, their ubiquitous use of Facebook and other social networking sites may set Possibilianism apart, said Darren Sherkat, a sociologist at Southern Illinois University at Carbondale who wrote “Beyond Belief: Atheism, Agnosticism, and Theistic Certainty in the United States,” in the journal Sociological Spectrum, as well as the upcoming book, “Religious Change in America.”

“We don’t know what the Internet can really do yet, in terms of religion,” he said. “Eighteen percent of Americans don’t believe in God, so this movement has the power to reach this untapped market, cheaply, through the power of the Internet.”

But unlike, say, Scientology, which also began as a scientist’s faith-based musings, Sherkat doubts that Possibilianism will spawn its own religion — which Eagleman firmly states is not his intention. Still, he is rushing to put out a second book, “Why I Am A Possibilian,” to clarify his philosophy before it spirals out of control online.

“It would be ironic if someone started a Church of Possibilianism, because in real movements, people bang on a podium and say, `This it what to believe,’ but Possibilianism is just the opposite,” he said, adding that he hopes the movement helps prompt more interfaith dialogue. “There are 2,000 religions and everyone believes just as fervently in theirs as you do in yours.”

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Of the 40 afterlife scenarios chronicled in “Sum,” and the hundreds more he has imagined over the years, Eagleman insists that none of them stand out for him as a personal favorite.

“Being a Possibilian, you can hold all these possibilities in your head and 4,000 more — they’re all equally improbable,” Eagleman said. “I’ve tapped into the pulse of something that’s been missing, that’s what people want. It doesn’t require anyone to be polarized, to fight and die for their particular version of the story.”