Steve Huffman, the thirty-three-year-old co-founder and C.E.O. of Reddit, which is valued at six hundred million dollars, was nearsighted until November, 2015, when he arranged to have laser eye surgery. He underwent the procedure not for the sake of convenience or appearance but, rather, for a reason he doesn’t usually talk much about: he hopes that it will improve his odds of surviving a disaster, whether natural or man-made. “If the world ends—and not even if the world ends, but if we have trouble—getting contacts or glasses is going to be a huge pain in the ass,” he told me recently. “Without them, I’m fucked.”

Huffman, who lives in San Francisco, has large blue eyes, thick, sandy hair, and an air of restless curiosity; at the University of Virginia, he was a competitive ballroom dancer, who hacked his roommate’s Web site as a prank. He is less focussed on a specific threat—a quake on the San Andreas, a pandemic, a dirty bomb—than he is on the aftermath, “the temporary collapse of our government and structures,” as he puts it. “I own a couple of motorcycles. I have a bunch of guns and ammo. Food. I figure that, with that, I can hole up in my house for some amount of time.”

Survivalism, the practice of preparing for a crackup of civilization, tends to evoke a certain picture: the woodsman in the tinfoil hat, the hysteric with the hoard of beans, the religious doomsayer. But in recent years survivalism has expanded to more affluent quarters, taking root in Silicon Valley and New York City, among technology executives, hedge-fund managers, and others in their economic cohort.

Last spring, as the Presidential campaign exposed increasingly toxic divisions in America, Antonio García Martínez, a forty-year-old former Facebook product manager living in San Francisco, bought five wooded acres on an island in the Pacific Northwest and brought in generators, solar panels, and thousands of rounds of ammunition. “When society loses a healthy founding myth, it descends into chaos,” he told me. The author of “Chaos Monkeys,” an acerbic Silicon Valley memoir, García Martínez wanted a refuge that would be far from cities but not entirely isolated. “All these dudes think that one guy alone could somehow withstand the roving mob,” he said. “No, you’re going to need to form a local militia. You just need so many things to actually ride out the apocalypse.” Once he started telling peers in the Bay Area about his “little island project,” they came “out of the woodwork” to describe their own preparations, he said. “I think people who are particularly attuned to the levers by which society actually works understand that we are skating on really thin cultural ice right now.”

In private Facebook groups, wealthy survivalists swap tips on gas masks, bunkers, and locations safe from the effects of climate change. One member, the head of an investment firm, told me, “I keep a helicopter gassed up all the time, and I have an underground bunker with an air-filtration system.” He said that his preparations probably put him at the “extreme” end among his peers. But he added, “A lot of my friends do the guns and the motorcycles and the gold coins. That’s not too rare anymore.”

Tim Chang, a forty-four-year-old managing director at Mayfield Fund, a venture-capital firm, told me, “There’s a bunch of us in the Valley. We meet up and have these financial-hacking dinners and talk about backup plans people are doing. It runs the gamut from a lot of people stocking up on Bitcoin and cryptocurrency, to figuring out how to get second passports if they need it, to having vacation homes in other countries that could be escape havens.” He said, “I’ll be candid: I’m stockpiling now on real estate to generate passive income but also to have havens to go to.” He and his wife, who is in technology, keep a set of bags packed for themselves and their four-year-old daughter. He told me, “I kind of have this terror scenario: ‘Oh, my God, if there is a civil war or a giant earthquake that cleaves off part of California, we want to be ready.’ ”

When Marvin Liao, a former Yahoo executive who is now a partner at 500 Startups, a venture-capital firm, considered his preparations, he decided that his caches of water and food were not enough. “What if someone comes and takes this?” he asked me. To protect his wife and daughter, he said, “I don’t have guns, but I have a lot of other weaponry. I took classes in archery.”

For some, it’s just “brogrammer” entertainment, a kind of real-world sci-fi, with gear; for others, like Huffman, it’s been a concern for years. “Ever since I saw the movie ‘Deep Impact,’ ” he said. The film, released in 1998, depicts a comet striking the Atlantic, and a race to escape the tsunami. “Everybody’s trying to get out, and they’re stuck in traffic. That scene happened to be filmed near my high school. Every time I drove through that stretch of road, I would think, I need to own a motorcycle because everybody else is screwed.”

Huffman has been a frequent attendee at Burning Man, the annual, clothing-optional festival in the Nevada desert, where artists mingle with moguls. He fell in love with one of its core principles, “radical self-reliance,” which he takes to mean “happy to help others, but not wanting to require others.” (Among survivalists, or “preppers,” as some call themselves, FEMA, the Federal Emergency Management Agency, stands for “Foolishly Expecting Meaningful Aid.”) Huffman has calculated that, in the event of a disaster, he would seek out some form of community: “Being around other people is a good thing. I also have this somewhat egotistical view that I’m a pretty good leader. I will probably be in charge, or at least not a slave, when push comes to shove.”

Over the years, Huffman has become increasingly concerned about basic American political stability and the risk of large-scale unrest. He said, “Some sort of institutional collapse, then you just lose shipping—that sort of stuff.” (Prepper blogs call such a scenario W.R.O.L., “without rule of law.”) Huffman has come to believe that contemporary life rests on a fragile consensus. “I think, to some degree, we all collectively take it on faith that our country works, that our currency is valuable, the peaceful transfer of power—that all of these things that we hold dear work because we believe they work. While I do believe they’re quite resilient, and we’ve been through a lot, certainly we’re going to go through a lot more.”

In building Reddit, a community of thousands of discussion threads, into one of the most frequently visited sites in the world, Huffman has grown aware of the way that technology alters our relations with one another, for better and for worse. He has witnessed how social media can magnify public fear. “It’s easier for people to panic when they’re together,” he said, pointing out that “the Internet has made it easier for people to be together,” yet it also alerts people to emerging risks. Long before the financial crisis became front-page news, early signs appeared in user comments on Reddit. “People were starting to whisper about mortgages. They were worried about student debt. They were worried about debt in general. There was a lot of, ‘This is too good to be true. This doesn’t smell right.’ ” He added, “There’s probably some false positives in there as well, but, in general, I think we’re a pretty good gauge of public sentiment. When we’re talking about a faith-based collapse, you’re going to start to see the chips in the foundation on social media first.”

How did a preoccupation with the apocalypse come to flourish in Silicon Valley, a place known, to the point of cliché, for unstinting confidence in its ability to change the world for the better?

Those impulses are not as contradictory as they seem. Technology rewards the ability to imagine wildly different futures, Roy Bahat, the head of Bloomberg Beta, a San Francisco-based venture-capital firm, told me. “When you do that, it’s pretty common that you take things ad infinitum, and that leads you to utopias and dystopias,” he said. It can inspire radical optimism—such as the cryonics movement, which calls for freezing bodies at death in the hope that science will one day revive them—or bleak scenarios. Tim Chang, the venture capitalist who keeps his bags packed, told me, “My current state of mind is oscillating between optimism and sheer terror.”