The catastrophe wasn’t what it seemed. It was an inside job, people whispered. Rome didn’t have to burn to the ground.

Nearly 2,000 years ago, after the Great Fire of Rome leveled most of the city, Romans questioned whether the emperor Nero had ordered his guards to start the inferno so he could rebuild Rome the way he wanted. They said the emperor had watched the blaze from the the summit of Palatine Hill, the centermost of the seven hills of Rome, plucking his lyre in celebration as countless people died. There’s no evidence of this maniacal lyre-playing, but historians today still debate whether Nero orchestrated the disaster.

What we do know is this: Conspiracy theories flourish when people feel vulnerable. They thrive on paranoia. It has always been this way.

So it’s understandable that, at this chaotic moment in global politics, conspiracy theories seem to have seeped out from the edges of society and flooded into mainstream political discourse. They’re everywhere.

That’s partly because of the richness of today’s informational environment. In Nero’s day, conspiracy theories were local. Today, they’re global. The web has made it easier than ever for people to watch events unfold in real time. Any person with a web connection can participate in news coverage, follow contradicting reports, sift through blurry photos, and pick out (or publish) bad information. The democratization of internet publishing and the ceaseless news cycle work together to provide a never-ending deluge of raw material that feeds conspiracy theories of all stripes.

From all over the world, likeminded people congregate around the same comforting lies, explanations that validate their ideas. “Things seem a whole lot simpler in the world according to conspiracy theories,” writes Rob Brotherton, in his book, Suspicious Minds: Why We Believe Conspiracy Theories. “The prototypical conspiracy theory is an unanswered question; it assumes nothing is as it seems; it portrays the conspirators as preternaturally competent; and as unusually evil.”

But there’s a difference between people talking about outlandish theories and actually believing them to be true. “Those are two very different things,” says Joseph Uscinski, a political science professor at the University of Miami and the co-author of the book American Conspiracy Theories. “There’s a lot of elite discussion of conspiracy theories, but that doesn’t mean that anyone’s believing them any more than they did in the past. People understand what conspiracy theories are. They can understand these theories as political signals when they don’t in fact believe them.” ...