All the leading immortalists started out in tech, and all had a father who died young (as Ray Kurzweil’s did when he was twenty-two), or absconded early (as Aubrey de Grey’s did before he was born). They share an early loss of innocence and a profound faith that the human mind can perfect even the human body. Larry Ellison, the co-founder of Oracle, lost his adoptive mother to cancer when he was in college—and later donated three hundred and seventy million dollars to aging research. “Death has never made any sense to me,” he told a biographer. “How can a person be there and then just vanish?” Bill Maris, who conceived of Calico, said that, when he pondered the inevitability of death, “I felt it was maybe our mission here to transcend that, and to preserve consciousness indefinitely.”

Immortalists fall into two camps. Those who might be called the Meat Puppets, led by de Grey, believe that we can retool our biology and remain in our bodies. The RoboCops, led by Kurzweil, believe that we’ll eventually merge with mechanical bodies and/or with the cloud. Kurzweil is a lifelong fixer and optimizer: early in his career, he invented the flatbed scanner and a machine that reads books aloud to the blind. Those inventions have improved dramatically in subsequent iterations, and now he’s positive that what he calls “the law of accelerating returns” for human longevity is about to kick in.

I met with Kurzweil at Google, where he is a director of engineering, but he emphasized that he was speaking in his private capacity as a futurist. Though a few days short of his sixty-ninth birthday, he looked much younger. After discovering, in his thirties, that he had Type 2 diabetes, he changed his life style radically and began taking supplements. He swallows some ninety pills a day, including metformin; Basis; a coenzyme called Q10, for muscle strength; and phosphatidylcholine, to keep his skin supple. “How does it look?” he asked me, plucking at his forearm. “Supple!” I said.

Kurzweil thinks of such efforts, which attempt to slow aging by using current technology, as Bridge One to indefinite longevity. But he also subscribes to the belief that the body is essentially a computer made up of overwritable data and updatable apps. Therefore, we’ll soon be in the midst of a biotech revolution, which will offer personally tailored immune therapies for cancer as well as organs grown from our own DNA. This is Bridge Two, which he believes will bring us to longevity escape velocity within about fifteen years. “I’m actually a little more optimistic than Aubrey,” he said. Bridge Three, which he expects us to cross by the two-thousand-thirties, is nanobots—blood-cell-size devices that will roam the body and the brain, cleaning up all the damage that de Grey wants to fix with medical interventions. “I used to call it the killer app of health technology,” Kurzweil said, “but that’s not a good name.”

When we cross Bridge Four, those same nanobots will connect our brains to a neocortical annex in the cloud, and our intelligence will quickly expand a billionfold. Once that transformation happens, in 2045, the Singularity occurs and we become like gods. “For a time, we’ll be a hybrid of biological and nonbiological thinking, but, as the cloud keeps doubling, the nonbiological intelligence will predominate,” Kurzweil said. “And it will be anachronistic, then, to have one body.” He raised his arms slightly and squinted at them, a carpenter troubled by a burl in the wood.

Kurzweil acknowledges that he was profoundly affected by the early death of his father, Fredric. Fredric was a brilliant conductor and pianist, but he worked incessantly to make ends meet and was often absent from the family. Kurzweil’s mother once observed, “It was hard on Raymond. He needed a father—and his father was never around.” Kurzweil has preserved fifty boxes of his father’s effects, everything from his letters and photographs to his electric bills, all pack-ratted into a storage facility in Newton, Massachusetts. He hopes to someday create a virtual avatar of his father and then populate the doppelgänger’s mind with all this information, as well as with his own memories of and dreams about his father, exhuming a Fredric Kurzweil 2.0.

“We have spent millennia rationalizing the tragedy of death—‘Oh, it’s natural, it’s the goal of life,’ ” Kurzweil told me. “But that’s not really how we feel when we hear that someone we love has died.” He fell silent, then reverted to the question of how realistic his father’s avatar would be, how consoling. “Passing a Fredric Kurzweil Turing test is getting easier and easier,” he said, smiling wryly, “because the people who knew him, like me, are getting older and older.”

The Meat Puppets, fighting off old age, must contend with evolutionary contingency. Jan Vijg, who co-authored a recent paper arguing that our life span is basically capped at a hundred and fifteen, told me, “Yes, our bodies are information-processing systems. But to fix the body-as-computer requires an in-depth understanding of what’s going on in your cells at a molecular level. And we don’t even know how many types of cells there are! Creating a human is not nearly as easy as creating an A.I., because we’re so very confusingly and unintelligently designed by random changes acted upon by natural selection.”

The RoboCops must contend with the boundaries of the human terrain. Osman Kibar, the C.E.O. of a biotech company called Samumed, told me, “We humans are very creative. When we hit a biological limit, we cheat—like Kurzweil, who’s saying, ‘Let’s change the definition of human.’ As each of our functions is uploaded or replaced, at some point you stop calling that a human and start calling it an A.I.” We already have technologies that work inside the body, such as pacemakers and cochlear implants. A paralyzed man recently typed eight words a minute by using a brain-computer interface inserted in his motor cortex. How long will it be before the advantages of scaling and precision manufacture can be applied to the whole body?

The 2045 Institute, started by a wealthy Russian inspired by Kurzweil’s time line, believes that we can at least begin making down payments on that moment. The institute’s Web site has an “immortality button,” which you click “to start the development of your own personalized immortal avatar.” You can select from among a remote-controlled robotic copy, a full-body prosthesis topped off by your transplanted head, and a top-of-the-line, wholly artificial body containing your uploaded essence, which will “achieve perfection of form and be no less attractive than the human body.”

The sticking point seems to be what to do about our heads, specifically our brains. The futurist Juan Enriquez told me, “We’ll be able to transplant a mouse head within five years. And then it gets really interesting—does Mickey remember Minnie?” At the moment, however, no one has figured out how to refresh Mickey’s brain biology, no matter which body it’s attached to. Neurons don’t regenerate, and we don’t grow new ones, except in the hippocampus. Stem cells imported into the brain don’t help; they just sit there, then die.

Benjamin Rapoport, a neurosurgery resident at Weill Cornell Brain and Spine Center who’s working on a project that would directly connect brains to A.I.s, said, “The question is, What is the fundamental you that is you? Most people feel it’s the mind. But can your mind exist only in a biological substrate that weighs 1.5 kilograms, is very wet, and floats like a jellyfish? Or could it conceivably exist someplace else?” In a computer, say. A two-way, high-bandwidth interface with the brain could be available within a decade, and scientists are already trying to map the hundred billion neurons in the brain and the hundred-trillion-plus connections between them—the “connectome,” as it’s infelicitously called. Currently, you can model someone’s brain at the synapse level only by slicing it up after the person is dead. Eventually, however, it seems possible that we could achieve “whole-brain emulation” with live subjects. There would then be permanent copies of our brains that would—we hope—themselves have consciousness.