On the evening of October 30, 1938, a seventy-six-year-old millworker in Grover’s Mill, New Jersey, named Bill Dock heard something terrifying on the radio. Aliens had landed just down the road, a newscaster announced, and were rampaging through the countryside. Dock grabbed his double-barrelled shotgun and went out into the night, prepared to face down the invaders. But, after investigating, as a newspaper later reported, he “didn’t see anybody he thought needed shooting.” In fact, he’d been duped by Orson Welles’s radio adaptation of “The War of the Worlds.” Structured as a breaking-news report that detailed the invasion in real time, the broadcast adhered faithfully to the conventions of news radio, complete with elaborate sound effects and impersonations of government officials, with only a few brief warnings through the program that it was fiction.

The next day, newspapers were full of stories like Dock’s. “Thirty men and women rushed into the West 123rd Street police station,” ready to evacuate, according to the Times. Two people suffered heart attacks from shock, the Washington Post reported. One caller from Pittsburgh claimed that he had barely prevented his wife from taking her own life by swallowing poison. The panic was the biggest story for weeks; a photograph of Bill Dock and his shotgun, taken the next day, by a Daily News reporter, went “the 1930s equivalent of viral,” A. Brad Schwartz writes in his recent history, “Broadcast Hysteria: Orson Welles’s War of the Worlds and the Art of Fake News.”

This early fake-news panic lives on in legend, but Schwartz is the latest of a number of researchers to argue that it wasn’t all it was cracked up to be. As Schwartz tells it, there was no mass hysteria, only small pockets of concern that quickly burned out. He casts doubt on whether Dock had even heard the broadcast. Schwartz argues that newspapers exaggerated the panic to better control the upstart medium of radio, which was becoming the dominant source of breaking news in the thirties. Newspapers wanted to show that radio was irresponsible and needed guidance from its older, more respectable siblings in the print media, such “guidance” mostly taking the form of lucrative licensing deals and increased ownership of local radio stations. Columnists and editorialists weighed in. Soon, the Columbia education professor and broadcaster Lyman Bryson declared that unrestrained radio was “one of the most dangerous elements in modern culture.”

The argument turned on the role of the Federal Communications Commission, the regulators charged with insuring that the radio system served the “public interest, convenience and necessity.” Unlike today’s F.C.C., which is known mainly as a referee for media mergers, the F.C.C. of the thirties was deeply concerned with the particulars of what broadcasters put in listeners’ ears—it had recently issued a reprimand after a racy Mae West sketch that so alarmed NBC it banned West from its stations. To some, the lesson of the panic was that the F.C.C. needed to take an even more active role to protect people from malicious tricksters like Welles. “Programs of that kind are an excellent indication of the inadequacy of our present control over a marvellous facility,” the Iowa senator Clyde Herring, a Democrat, declared. He announced a bill that would require broadcasters to submit shows to the F.C.C. for review before airing. Yet Schwartz says that the people calling for a government crackdown were far outnumbered by those who warned against one. “Far from blaming Mr. Orson Welles, he ought to be given a Congressional medal and a national prize,” the renowned columnist Dorothy Thompson wrote.

Thompson was concerned with a threat far greater than rogue thespians. Everywhere you looked in the thirties, authoritarian leaders were being swept to power with the help of radio. The Nazi Ministry for Public Enlightenment and Propaganda deployed a force called the Funkwarte, or Radio Guard, that went block by block to insure that citizens tuned in to Hitler’s major broadcast speeches, as Tim Wu details in his new book, “The Attention Merchants.” Meanwhile, homegrown radio demagogues like Father Charles Coughlin and the charismatic Huey Long made some people wonder about a radio-aided Fascist takeover in America. For Thompson, Welles had made an “admirable demonstration” about the power of radio. It showed the danger of handing control of the airwaves over to the state. “No political body must ever, under any circumstances, obtain a monopoly of radio,” she wrote. “The greatest organizers of mass hysterias and the mass delusions today are states using the radio to excite terrors, incite hatreds, inflame masses.”

Donald Trump’s victory has been a demonstration, for many people, of how the Internet can be used to achieve those very ends. Trump used Twitter less as a communication device than as a weapon of information warfare, rallying his supporters and attacking opponents with hundred-and-forty-character barrages. “I wouldn’t be here without Twitter,” he declared on Fox News in March. Yet the Internet didn’t just give him a megaphone. It also helped him peddle his lies through a profusion of unreliable media sources that undermined the old providers of established fact. Throughout the campaign, fake-news stories, conspiracy theories, and other forms of propaganda were reported to be flooding social networks. The stories were overwhelmingly pro-Trump, and the spread of whoppers like “Pope Francis Shocks World, Endorses Donald Trump for President”—hardly more believable than a Martian invasion—seemed to suggest that huge numbers of Trump supporters were being duped by online lies. This was not the first campaign to be marred by misinformation, of course. But the sheer outlandishness of the claims being made, and believed, suggested to many that the Internet had brought about a fundamental devaluing of the truth. Many pundits argued that the “hyper-democratizing” force of the Internet had helped usher in a “post-truth” world, where people based their opinions not on facts or reason but on passion and prejudice.

Yet, even among this information anarchy, there remains an authority of sorts. Facebook and Google now define the experience of the Internet for most people, and in many ways they play the role of regulators. In the weeks after the election, they faced enormous criticism for their failure to halt the spread of fake news and misinformation on their services. The problem was not simply that people had been able to spread lies but that the digital platforms were set up in ways that made them especially potent. The “share” button sends lies flying around the Web faster than fact checkers can debunk them. The supposedly neutral platforms use personalized algorithms to feed us information based on precise data models of our preferences, trapping us in “filter bubbles” that cripple critical thinking and increase polarization. The threat of fake news was compounded by this sense that the role of the press had been ceded to an arcane algorithmic system created by private companies that care only about the bottom line.

Not so very long ago, it was thought that the tension between commercial pressure and the public interest would be one of the many things made obsolete by the Internet. In the mid-aughts, during the height of the Web 2.0 boom, the pundit Henry Jenkins declared that the Internet was creating a “participatory culture” where the top-down hegemony of greedy media corporations would be replaced by a horizontal network of amateur “prosumers” engaged in a wonderfully democratic exchange of information in cyberspace—an epistemic agora that would allow the whole globe to come together on a level playing field. Google, Facebook, Twitter, and the rest attained their paradoxical gatekeeper status by positioning themselves as neutral platforms that unlocked the Internet’s democratic potential by empowering users. It was on a private platform, Twitter, where pro-democracy protesters organized, and on another private platform, Google, where the knowledge of a million public libraries could be accessed for free. These companies would develop into what the tech guru Jeff Jarvis termed “radically public companies,” which operate more like public utilities than like businesses.