“In statistics, a problem akin to apophenia is a Type I error, or false positive,” wrote Katy Waldman in a 2014 Slate article about the phenomenon. “It means believing something is real when it isn’t, based on a misleading pattern in the data.”

Truthers, the nickname often used for 9/11 conspiracy theorists, have routinely looked to Hollywood for hints that the terrorist attacks were foretold. Along with Back to the Future, some of the films that conspiracy theorists say contain warnings include: Armageddon (1998), The Matrix (1999), Gremlins 2 (1990), Rugrats in Paris (2000), Godzilla (1998), Terminator 2 (1991), Super Mario Bros. (1993), The Patriot (2000), Traffic (2000), and several others. The so-called clues, in most cases, are not compelling or even particularly eerie. Some of the films are flagged simply for referencing the numbers 9 and 11 in close proximity—on the hands of a watch, for example, or in dialogue about the birth of a 9-pound-11-ounce baby.

The fact that the people looking for conspiracies find them in Hollywood films is a reflection of the people, not the films—or even the larger prevalence of such theories. “There’s also a psychological component that underlies it,” Uscinski said, “an environmental effect that essentially triggers something that’s already there. Some people are just predisposed to view conspiracies lurking behind every corner.

“So everything that happens, I guarantee, you go to the Internet and find people who believe there’s a conspiracy about it,” Uscinski said. “Whether it was Sandy Hook or Aurora or the Deepwater Horizon oil spill. Everything that’s big in the news, people who have a conspiracy viewpoint will view it as the product of a conspiracy.”

When you start looking for conspiracy theories online, they seem to be everywhere. Dave Matthews, Nostradamus, Donald Trump, and the typeface Wingdings all predicted 9/11, according to various websites. Elsewhere, you’ll find reports that America is on the brink of a second civil war, and that Elvis and Michael Jackson are still alive.

Fundamentally, conspiracy theories haven’t actually changed much over the course of hundreds of years. “Ubiquitous access to all sorts of information is making at least some of us seem less, rather than more, rational and tolerant," wrote Carl Jensen and Rom Harré in the book, Beyond Rationality. "The problem, however, is certainly not in the information, which is agnostic. It is more likely a result of the filters we construct and those that are constructed for us.”

To track conspiracy theories over time, Uscinski and his co-author Joseph Parent scoured a century’s worth of letters to the editor of The New York Times. Among some of the themes they found were the beliefs that American scientists were controlling the weather (1958), the Roosevelt administration was secretly communist (1936), England and Canada were conspiring to overthrow portions of the United States (1890), and a bill written to protect sheep was passed with the intention of killing off all domestic dogs (1917).