The promise of heaven is one of the most powerful and motivating beliefs in human history.
In a survey by ABC News, nearly nine out of 10 Americans said they believed heaven existed.
But what exactly do people envision when they think of an afterlife, and what do they believe is required to get there?
Is heaven a myth dreamed up to give our lives meaning? Or is it a real place?
Barbara Walters traveled to India, Israel, and throughout the United States, talking to religious leaders of every major faith, believers and nonbelievers, scientists, celebrities … and even terrorists, in search of a better understanding of just what people believe when it comes to the afterlife.
From Valhalla to Nirvana
Every culture has wrestled with the question of an afterlife, and most have come to a similar conclusion: The bad end up in hell, the good go to heaven.
If you were a Viking who died in battle, fierce goddess warriors known as the Valkyries would carry you to Viking Heaven, Valhalla, where you would join an eternal feast. The Romans thought they became immortal and were spirited off to Paradise on a fiery four-horse chariot.
The early Christians and Jews believed that man was not pure enough to enter the Kingdom of Heaven as flesh and blood. They believed all people were transformed into spiritual beings, filling Heaven with angels.
That belief has changed over the centuries, but angels still have an important connection with heaven. In cities all over the world, angels can be seen in watchful poses.
"We believe that they are the ones who take care of us. They are the messengers of God. They are the ones who are God's very special friends and his servants," says Cardinal Theodore McCarrick, former archbishop of Washington, D.C.
"I always think of heaven as being a place where we won't have any troubles anymore. Heaven is a place where there will be peace and tranquility," McCarrick says. As a Catholic, McCarrick believes heaven is more than a spiritual place. Catholics, he explained, believe the body is resurrected. "I'm looking forward to meeting my mom and dad and the rest of my family," he adds.
The Rev. Dr. Calvin Butts, pastor of New York's famed Abyssinian Baptist Church, tells Walters he has had many visions of heaven over the years. He describes heaven as "no tears, no mourning, no suffering. It's eternal joy and happiness because you are at one with God."
Butts is certain of heaven's existence, but says it's in an indescribable dimension. "Heaven is in another dimension. So you don't necessarily have to look up but you can look out and see heaven. Heaven is a fourth dimension if you will."
Walters traveled to India where she met with the Dalai Lama, considered by Buddhists to be the reincarnated Buddha. The Dalai Lama says that the purpose of life is to be happy, and that you can accomplish that by "warm-heartedness." He tells Walters heaven "is [the] best place to further develop the spiritual practice … for Buddhists the final goal is not just to reach there, but to become Buddha. [It's] not the end."
As a Buddhist, he believes in reincarnation and that people can have second lives as animals. "If someone do[es] very bad, badly … kill or steal … [he] could be born in an animal body."
Walters also talks to actor Richard Gere, a longtime follower of Buddhism. "I don't think necessarily heaven and hell happen in some other life. I think it's right now," Gere says.
Imam Feisal Abdul Rauf, founder of the American Society for Muslim Advancement, tells Walters he believes heaven is indeed a physical place, but getting there depends on your behavior in this life. "The real life is the next life … and based upon how we live this life, it determines where we shall be in the next. We are told we will be in comfortable homes, reclining on silk couches … so we're given the delights of sex, the delights of wine, the delights of food with all of their positive things without their negative aspects."
The promise of heaven plays a central role in the life of evangelical Pastor Joel Osteen.
America's evangelicals see themselves as the purist version of the faith, with a God-given mission to save the world.
These days, they are more influential than ever. Osteen's televised sermons attract about 7 million viewers on Sunday mornings, and 36,000 evangelicals pack his Lakewood church in Houston every week, the largest weekly religious gathering in the country.
Evangelicals believe that a person can get to heaven only if he or she believes in Christ and if he or she is born again. So what happens to everyone else?
"I think only God can be the judge of that," Osteen said. "I can't be the judge of other people. … The Christian faith shows us that Christ's forgiveness is available to anybody. All we have to do is call on the name of the Lord. … I don't think there's any guarantee in the Scripture that we [go to heaven] if we do not have a relationship with Christ."
Rabbi Neil Gillman, a professor of philosophy at New York's Jewish Theological Seminary, expresses Judaism's perspective on the afterlife. "For the past 2,000 years, most Jews believed that at death, the body and the soul separate, the body is interred and disintegrates in the earth, the soul goes off to be with God," he tells Walters. But that's not the end of the story. "At the end of days, God will resurrect bodies, will reunite body and soul, and the individual will come before God to account for his or her life," Gillman says.
The Skeptics and Non-Believers
Walters also speaks with scientists who say they're beginning to understand why so many people believe in heaven. Still, they have yet to come up with any proof that it exists.
For most people, proof of heaven's existence is not necessary. Faith is all they need. Dr. Dean Hamer, a geneticist at the National Institutes of Health, thinks he has figured out why this faith comes easily to some, but eludes others. "Whether a person is spiritual or not is not necessarily a matter of their will. It may be something innate about their personality," Hamer says.
Hamer suspects spirituality might be a personality trait encoded in our genes. He began his research by asking more than 1,000 people to answer a series of questions about faith and spirituality. He then tested DNA from the study participants and found that those who scored highest on his survey had a mutation of at least one gene that seemed to affect their level of spirituality. He named it "the God gene."
"It's a gene that's called VMAT2 and we can isolate it, and we can study it in detail. … 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 says.
Hamer also notes that researchers have been able to detect changes in the brain when people are in the midst of intense prayer or meditation.
Dr. Andrew Newberg, a neuroradiologist at the University of Pennsylvania, is one of those researchers. Newberg says his research shows a marked increase in activity in the frontal regions of the brain while people meditate. "At the same time," he adds, "the parts of the brain that monitor our sense of time and space became less active."
Newberg says this contributes to an individual's feeling of "losing that sense of self." The feeling, he says, is "attributed to God, for example. And then they feel that God is providing them that energy, that feeling."
But for Ellen Johnson, president of the American Atheists, science or no science, heaven is a myth.
"Heaven doesn't exist, hell doesn't exist. We weren't alive before we were born and we're not going to exist after we die. I'm not happy about the fact that that's the end of life, but I can accept that and make my life more fulfilling now, because this is the only chance I have," she says.
'Death Trips' to Heaven
Walters also talks with people who feel certain of heaven's existence, apart from their faith, because they believe they've had a glimpse of it in near-death experiences.
A U.S. News & World Report from the late 1990s says as many as 18 million Americans believe they have had near-death experiences that gave them a glimpse of the afterlife.
Dianne Morrissey tells Walters she felt the "white light of God" when she was electrocuted. "My near-death experience changed everything about me … There is not a single experience on Earth that could ever be as good as being dead," she said.
British psychologist Susan Blackmore has spent decades searching for a scientific explanation. "When the oxygen levels fall in the brain … you get massive over-activity in the brain. … I think there is a true transformation, but not because you've been to heaven."
Family, Children and Heaven
Walters talks with California's first lady, Maria Shriver, whose early experiences with loss as a member of the Kennedy family prompted her to write a book about heaven for children. "I had, growing up, a lot of questions about these deaths that occurred in my family with no person to really talk to them about it," she says.
"My daughter, who was about 6 or 7 at the time, started asking me a lot of the same questions that I had had as a child, really basic questions: 'Why do you put somebody in a coffin? Where does she go now? Is she scared in the box? Can she breathe in the box?' And what was interesting," Shriver adds, "was that she started answering the questions for herself. So I started writing down her answers."
Walters also talks with Mitch Albom, author of "The Five People You Meet in Heaven," to get his personal take on the afterlife.
Albom tells Walters, "There's one thing I would say about heaven. If you believe that there's a heaven, your life here on Earth here is different. You may believe that you're gonna see your loved ones again. So the grief that you had after they're gone isn't as strong. You may believe that you'll have to answer for your actions. So the way you behave here on Earth is changed. So in a certain way, just believing in the idea of heaven is heavenly in and of itself," he says.