On Dec. 11, 2002, 42-year-old Deb Foster checked into Scripps Memorial Hospital in San Diego to give birth. Her doctors performed a successful Caesarean section, delivering her second child -- a healthy baby girl named Bryce. Her family was thrilled, especially her husband, Andy, and their one and a half-year-old son, Christopher. Within hours, however, Foster was fighting for her life.
"It was as if my breath was knocked out of me, and I couldn't breathe. I said: 'I'm dying. I'm dying. Help me,'" Foster recalled.
She had suffered an amniotic fluid embolism -- a life-threatening condition. "It [the embolism] went in through my heart into my lungs and shut everything down. I was flat-lined. There wasn't a pulse. I was dead," Foster said. The doctors later confirmed that Foster was clinically dead for about four minutes. As they struggled to bring her back to life, she says she took an unforgettable journey.
"I immediately went to a different place. I was on a staircase, and the staircase went as high up into the sky as you can imagine and the sky was the most incredible color of blue that does not exist in this life. It's not on any color palette. I've tried to find it after this experience. It doesn't exist."
Foster said she had company during her journey. "There were dogs and cats going up and down the staircase, and they were very gleeful. And you could just tell they were so intensely happy. ... I was in this place of incredible peace. There wasn't any pain. It was serene. It was the perfect moment," she said.
Foster believes she saw a glimpse of heaven.
British psychologist Dr. Susan Blackmore spent decades searching for a scientific explanation for the near-death experience. She developed a theory that these experiences can be explained as the product of a dying brain. "We know that when the oxygen levels fall in the brain, the inhibitory systems start to fail first and you get massive overactivity in the brain. It's kind of going wild in there. I think there is a true transformation but not because you've been to heaven," she said.
Many scientists and doctors believe that the near-death experience is simply the function of a dying brain, but Foster -- and thousands of others who have had similar experiences -- believe otherwise.
"I know what I experienced, and no scientist can deny the near-death experience. There is no proof that it doesn't exist. It exists, and I was there," she said.
What's behind these visions of an afterlife, the human craving for eternity, the sense that another world awaits us when we die? Is it innate? Is it something we learn?
Walters talks with both scientists and religious leaders to examine the question.
Dean Hamer, a geneticist at the National Institutes of Health, tells Walters he thinks he has figured out why faith comes easily to some, but eludes others. His research suggests that some people may have a genetic predisposition toward faith. "This particular gene controls certain chemicals in the brain. And those chemicals affect how consciousness works. They affect the way that our feelings react to the events around us," he said.
Walters also traveled to the Himalayas in northern India and spoke with Buddhism's most esteemed believer, his holiness, the Dalai Lama, who does not believe in God but does believe in a form of heaven.
In spite of the continuing inhumanity, war, suffering and disease that still plague the Earth, the Dalai Lama said he believed the world today was closer to heaven than to hell.
Walters also met with Palestinian terrorists at a high-security prison in Israel to ask about their concept of heaven that underlies their willingness to kill others in order to martyr themselves.
When asked whether he wanted non-Muslims to go to hell, Jihad Jarrar, one of the terrorists, responded: "No, it's not what I want. It's what God wants. It's not what I want. You should follow Mohammed."
And those who don't, "will go to hell, of course," he added.
Prominent Christian leaders explained their own perceptions of heaven.
The Rev. Dr. Calvin Butts, pastor of New York's famed Abyssinian Baptist Church in Harlem, N.Y., told Walters he too had seen heaven. He described heaven as "eternal joy and happiness because you are at one with God" -- and a place where he'll have his hair back.
But who will be allowed to enter heaven is a matter of debate for religious leaders of different faiths. Pastor Ted Haggard believes only those who accept Jesus Christ as their personal savior will enter heaven. Those who don't will go to hell, Haggard believes. "I don't want to communicate a bad attitude or anything like that. But the issue is this is a guarantee for eternal life," he told Walters.
In addition to these religious figures, Walters talks with ordinary people about their beliefs and how those beliefs make a difference in their daily lives.