Recently, at a wedding reception, I polled some friends about immortality. Suppose you could upload your brain tomorrow and live forever as a human-machine hybrid, I asked an overeducated couple from San Francisco, parents of two young daughters. Would you do it? The husband, a 42-year-old M.D.-Ph.D., didn't hesitate before answering yes. His current research, he said, would likely bear fruit over the next several centuries, and he wanted to see what would come of it. “Plus, I want to see what the world is like 10,000 years from now.” The wife, a 39-year-old with an art history doctorate, was also unequivocal. “No way,” she said. “Death is part of life. I want to know what dying is like.”