I’ve known conspiracy theorists my entire life. In fact, there’s probably a little bit of conspiracy theorist in each of us, myself included. (Don’t get me started on Game 6 of the 2002 N.B.A. Western Conference Finals.) We’re naturally drawn to mysteries, rumors of secret backroom deals and tales of intrigue. Some dive in more deeply and recklessly than others, but showing an interest in the story behind a story isn’t just human nature, it can also be a sign of healthy skepticism, and an unwillingness to take official or conventional explanations at face value.

When I was growing up, the father of one of my friends was fascinated by the J.F.K. assassination. Another friend’s dad devoured accounts of U.F.O. encounters. They weren’t weird or worrisome or dangerous men, just quirky and interesting. Under no circumstance were they a threat to American democracy.

But in recent years I’ve encountered, both in person and online, a phenomenon that is different from the belief or interest in any given conspiracy theory. People don’t just have strange or quirky ideas on confined subjects. They have entire worldviews rooted in a comprehensive network of misunderstandings and false beliefs.

And these aren’t what you’d call low-information voters. They’re some of the most politically engaged people I know. They consume news voraciously. They’re perpetually online. For them, politics isn’t just a hobby; in many ways, it’s a purpose.

There is a fundamental difference between, on the one hand, someone who lives in the real world but also has questions about the moon landing, and on the other, a person who believes the Covid vaccine is responsible for a vast number of American deaths and Jan. 6 was an inside job and the American elite is trying to replace the electorate with new immigrant voters and the 2020 election was rigged and Donald Trump is God’s divine choice to save America.

Such individuals don’t simply believe in a conspiracy theory, or theories. They live in a “bespoke reality.” That brilliant term comes from my friend Renée DiResta, the technical research manager at the Stanford Internet Observatory, and it refers to the effects of what DiResta calls a “Cambrian explosion of bubble realities,” communities “that operate with their own norms, media, trusted authorities and frameworks of facts.”