Is heaven for real? And if so, which heaven? For some, heaven is the Christian kind of afterlife that was described by a 4-year-old boy in the book and movie titled "Heaven Is for Real." For others, it's Islamic rivers of wine and honey, or Buddhist enlightenment, or a Hindu gateway to the eternal.

For those of a purely scientific bent, intimations of heaven might be just the impulses generated by a fading brain, or a physiological defense mechanism triggered by trauma.

In the new book "Visions of Heaven," religion writer Lisa Miller surveys all of those heavens and their centuries-old historical roots. Reflecting on such visions is particularly apt this weekend, as Christians celebrate Easter and Jews celebrate Passover. But Miller says she's also intrigued in heavenly visions that are inspired by cyberspace rather than Scripture.

"There are people who believe in a fourth dimension, where heaven is just on the other side of some wall," Miller told NBC News. "An idea that I'm actually more interested in is that of the Internet as a place like heaven. People gather in worlds that suit them, that are like them, where they meet each other based on similar interests. There's a kind of infiniteness to the Internet that's similar to ideas of heaven, and a kind of democracy. The parallels have definitely been drawn there, and I think they're interesting."

Shifting visions

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Miller noted that the classic vision of heaven, ranging from the Book of Revelation to "Heaven Is for Real," tends to endorse a traditional religious view. "You go to heaven, you look around and it proves that Jesus Christ is on the throne, and the angels are there. 'I saw it with my own eyes and it's true.'"

But recent studies have shown a gradual decline in religious commitment among Americans'

"Because Americans are increasingly so detached from religious traditions, what you get is a similar detachment in visions and images of heaven. ... The images can be so much more anything they want," Miller said.

For these people, a personalized vision of heaven might take the form of a perfect afternoon on the beach, or a dinner party, or a concert — as reflected in such afterlife movies as "Defending Your Life" or "The Lovely Bones."

"What religious traditionalists would say is, 'That's fine, metaphors are always fine. But where's the idea of God in those images?'" she said. "That's a fair critique. Heaven has become increasingly not a place where God lives but much more of a place where we can have everything we want."

The Church of Facebook?

Is there a cybernetic heaven ahead? Some researchers have speculated that virtual personalities, like the one played by Johnny Depp in the movie "Transcendence," could provide a kind of immortality: Even after you die, the family you left behind could interact with your simulated self.

Miller thinks Facebook memorial pages might serve as models for that kind of online afterlife.

"Look, it was a very popular idea in the Middle Ages that the dead are with us ... and we can invoke their spirits, we can refer to them, they live on in our lives," Miller said. "And when the Facebook page of somebody that you love is still up and live, that idea is almost literal. There they are. They're among us. We can talk to them, and we can talk to each other about them. We can post things that may be like prayers, on their Facebook page.

"The idea of the saints being among us is a very powerful Christian idea," she said. "And the Internet makes that possible in a really moving way for a lot of people."