Seated at the head of a table for 12 with a view of the city's soaring skyline, Peter Thiel was deep in conversation with his guests, scientists whose research was considered radical, even heretical.

It was 2004, and Thiel had recently made a tidy fortune selling PayPal, which he co-founded, to eBay. He had spent what he wanted on himself — a posh penthouse suite at the Four Seasons Hotel and a silver Ferrari — and was now soliciting ideas to do good with his money.

Among the guests was Cynthia Kenyon, a molecular biologist and biogerontologist who had garnered attention for doubling the life span of a roundworm by disabling a single gene. Aubrey de Grey, a British computer scientist turned theoretician who prophesied that medical advances would stop aging, was also there. As was Larry Page, co-founder of Internet search darling Google. The focus kept returning to one subject: Was death an inevitability — or a solvable problem?

A number of guests were skeptical about achieving immortality. But could science and technology help us live longer, to, say, 150 years? Now that, they agreed, was a worthy goal.

Within a few months, Thiel had written checks to Kenyon and De Grey to accelerate their work. Since then he has doled out millions to other researchers with what he calls "breakout" ideas that defy conventional wisdom.

"If you think you can only do very little and be very incremental, then you'll work only on very incremental things. It's self-fulfilling," said Thiel, 47. "It's those who have an optimism about what can be done that will shape the future."

He and the tech titans who founded Google, Facebook, eBay, Napster and Netscape are using their billions to rewrite the nation's science agenda and transform biomedical research. Their objective is to use the tools of technology — the chips, software programs, algorithms and big data they used in creating an information revolution — to understand and upgrade what they consider to be the most complicated piece of machinery in existence: the human body.

The entrepreneurs are driven by a certitude that rebuilding, regenerating and reprogramming patients' organs, limbs, cells and DNA will enable people to live longer and better. The work they are funding includes hunting for the secrets of living organisms with insanely long lives, engineering microscopic nanobots that can fix your body from the inside out, figuring out how to reprogram the DNA you were born with, and exploring ways to digitize your brain based on the theory that your mind could live after your body expires. "I believe that evolution is a true account of nature," as Thiel put it. "But I think we should try to escape it or transcend it in our society."

Oracle founder Larry Ellison has proclaimed his wish to live forever and donated more than $430 million to anti-aging research. "Death has never made any sense to me," he told his biographer, Mike Wilson. "How can a person be there and then just vanish, just not be there?"

During the first stage of their careers, the technologists spent their time solving problems in an industry that might seem glamorous but that in the grand scheme of things has been built on automating mundane tasks: how to pay for a book online, stream a TV episode onto a phone and keep tabs on friends. In contrast, they describe their biomedical research ventures in heroic terms reminiscent of science-fiction plots, where the protagonist saves humanity from destruction through technological wizardry.

Their confidence in that wizardry and their own ideas may lead them to underestimate the downsides and even dangers of the work they are funding, say some science philosophers, historians and economists. Their research in stem cells, neuroscience, genetically modified organisms and viruses, for example, tinkers with nature in big ways that easily could go awry — and operates in a largely unregulated space.

Their work to slow or stop aging, if successful, is also likely to lead to broader societal upheaval, increasing pressure on natural resources and on the economy, as people live longer, work longer and imperil already strained entitlements such as Social Security. Life extension also would radically change the most important building block of society: the family. No one seems able to predict what life might be like when half a dozen or more generations are alive simultaneously.

Laurie Zoloth, a bioethicist at Northwestern University, worries that some of the billionaires' obsession with longevity may be driven as much by hubris as a desire to do public good.

"It's incredibly exciting and wonderful to be part of a species that dreams in a big way," she said. "But I also want to be part of a species that takes care of the poor and the dying, and I'm worried that our attention is being drawn away to a glittery future world that is fantasy and not the world we live in."

The way that entrepreneur-philanthropists are transforming American society is reminiscent of the turn of the 20th century, when Andrew Carnegie and John D. Rockefeller led a handful of wealthy industrialists to shape real change in the world. They set up schools, art museums and public libraries that institutionalized their ideals of democracy and equality.

But the philanthropists of today's Gilded Age are more numerous and became rich faster and younger than their predecessors of a century ago.

Hospitals and research centers have long been preferred beneficiaries of philanthropists. But instead of just writing checks to existing institutions, many of the technologists are pioneering new approaches for how the work should be done and how to measure success.

For many of the tech entrepreneurs, interest in medical science is personal. Sean Parker, 34, the Napster co-founder, suffers from life-threatening food allergies and has family members with severe autoimmune disorders. He has donated millions to finding a cure for allergies and to new cancer therapies.

Google's Sergey Brin, 41, has proposed a new kind of science that starts with masses of DNA and a community of people with certain genes. Brin has a mutation of the LRRK2 gene that is associated with a higher risk of Parkinson's disease, and has said he thinks the new approach could be "transformational." He has donated $150 million to the effort.

America remains deeply ambivalent about using new medical treatments to live radically longer lives. In a 2013 survey conducted by the Pew Research Center, 51 percent said they believed treatments to slow, stop or reverse aging would have a negative impact on society. Fifty-eight percent said treatments that would allow people to live decades longer would be "fundamentally unnatural."

Leon Kass, a physician and ethicist, poses a philosophical question: "Could life be serious or meaningful without the limit of mortality?"