For 9_demon_bag, who asked that I refer to him by his screen name, the experience of learning that C-3PO wasn’t completely gold was disturbing. Had he been wrong for all those years about a character from Star Wars, or was something stranger at work? Searching online, he discovered that he was not alone.

“My very first Mandela Effect was C-3PO’s leg. I didn’t recall any silver in it. In the months afterwards I went looking for evidence, for some proof of what had happened.”

Belief in the Mandela Effect goes beyond simply noticing we’ve remembered something incorrectly. It entails a search for more complex explanations for our collective false memories, proof that the world has malfunctioned, rather than the human mind. But while most of r/MandelaEffect agrees something is going on, no one can agree for certain why it’s happening. One believer, writing on Reddit , turns to the metaphysical for an explanation:

The effect takes its name from the late Nelson Mandela, who, as some people remember, died in the 1980s, in prison in South Africa, rather than in 2013 as recorded history shows. Another popular Mandela Effect concerns the children’s book series The Berenstain Bears—yes, it’s Berenst_a_in, not Berenst_e_in. There’s also an ongoing search for a film titled Shazaam, starring the comedian Sinbad , which does not exist even though legions of people remember it. Other effects are more trivial: It’s Froot (not Fruit) Loops cereal, Jif (not Jiffy) peanut butter, and the Fruit of the Loom clothing logo (does not feature a cornucopia).

The Mandela Effect is the name given to the phenomenon of remembering something differently from how it actually is, and 9_demon_bag is now a moderator of the biggest community on Reddit dedicated to discussing it. r/MandelaEffect was founded in 2014, and currently hosts more than 120,000 subscribers.

What is it, then? A cultural meme? A bona fide psychological “condition”? To define the Mandela Effect is to explain it, and, so far, no one really can.

“I think one of the reasons we have one of the larger [subreddits] on this subject is that we invite everyone to participate,” 9_demon_bag told me. “We’re not only looking for positive confirmation that people remember things differently. We’d like to hear the other side.” Controversy is inevitable, because each post can be read as an invitation to debate whether the author is correct or is possibly going mad. Even the question of what a Mandela Effect actually is or isn’t remains unsettled. Links to conspiracy sites are banned on r/MandelaEffect, and figures like Fiona Brome, a paranormal researcher who coined the term in 2009 and who runs MandelaEffect.com, are adamant that the phenomenon is not a conspiracy theory.

On r/MandelaEffect, small inconsistencies become life altering. Noticing an effect sets people on a mission, seeking out further effects, studying them, and questioning the very nature of reality. Their explanations are by turns mundane and metaphysical; some are skeptics, believing that the mind is playing tricks on itself. Others link the Mandela Effect to conspiracies involving the Large Hadron Collider and the rupture of the space-time continuum, or to flat-earth theories. Some argue that we’re currently living inside a simulation controlled by a quantum computer, and are suspended in a glitching, digital afterlife.

The most dedicated keep written diaries and collect evidence, both digital and physical. During the first two years, after noticing C-3PO’s leg, 9_demon_bag said he amassed as much information as possible. “Honestly,” he told me, “it’s interesting in that some of the things you first remember when you’ve ‘downloaded’ this whole idea and looked at it are not necessarily the same things you see when you open it back up.”

“When you discover that this is real to you, that it’s a genuine effect, and that your memories are different to what you see, it hits everyone a little bit differently,” 9_demon_bag said. “For the first few days you’re looking for direction, you’re trying to figure out what just happened.” Confusion is a running theme, “but everyone tries to stay grounded, and the community helps with that.” Commenters turn to each other for reassurance, and to document potential “flip-flops”: things that change in the blink of an eye.

For all the talk of scientific theories and evidence-based analysis, there is a mysticism to the Mandela Effect. It functions as a philosophical prompt, confronting the _unheimlich—_the familiar yet eerily different—and finding in it proof of an afterlife (“Heaven is just like Earth except with Froot Loops instead of Fruit Loops,” one post proposes ), or evidence of an earthly conspiracy (another claims “90% Of The Main Sub Is Either AI Or Government Trying To Cover Up The fact that ME Is Real”). It becomes a canvas for further theorizing; explanations can be science-based, religious, as broad as the imagination itself.

“It has an existential aspect to it,” the neuroscientist Ylva Østby told me, “because if you can’t remember, can you trust yourself anymore?” Together with her sister, Hilde, Østby wrote Adventures in Memory: The Science and Secrets of Remembering and Forgetting , a book about landmark scientific studies of memory that considers the role of art, popular culture, community, and self-image in how memory functions, depicting it as complex, unpredictable, and social. Stories are repeated, the past is deconstructed and reassembled with every telling, and it is natural, Østby stressed, that we forget far more than we remember. “It’s actually more normal to not remember than it is to remember your experiences,” Østby explained. “All the details of your everyday life are filtered away immediately so that you don’t have to hold on to them. When you think about that, it leads to a feeling of loss, of losing control, and that is scary. But we simply have to live with that.”

In particular, the community is marked by a distrust of technology, of media, and of figures of authority (in one proposed explanation, Donald Trump is a time traveler linked to CERN , the Manhattan Project, and mass mind control). Posts made to r/MandelaEffect attempt to assemble a communal memory and, perhaps inadvertently, a picture of American childhood, because many of the effects relate to English-language films, foods, and various pop culture that came from the States in the 1990s. This, coupled with a spike in online mentions of the phrase “Mandela Effect” in late 2016, shows a predominantly US phenomenon surfacing around the same time as the term “fake news,” and encompassing the fear, confusion, and distrust that has come to characterize life online.

This is the problem with the Mandela Effect: efforts to write down effects when they first happen, and to subsequently track them (with diaries, material evidence, or using cryptography, as some have attempted) are drafted into the phenomenon and are liable to change, too. Notes disappear, web links mysteriously rot, computers develop bad sectors and magically delete files, and the believer is left questioning everything except their faith in the Mandela Effect itself.

There’s also a linguistic aspect to some Mandela Effects, which I can comment on from a lifetime of people bungling my last name as “Kilberd” (it’s Kiberd). For whatever reason, many people expect an “l” in there, similar to the way some expect to see “Beren stein.”

Given the level of news coverage he received in the 80s and 90s, it might also be easy enough to picture Nelson Mandela dying in prison, although it’s unlikely anyone from South Africa would make that mistake. “This is related to how prone we are to using our imagination,” Østby said. “People who are more prone to fantasy, and to using visual imagery, are also more prone to having false memories. That’s not because there’s something wrong with them, it’s just that the memory system we have interacts so much with imagery.”

The news, especially, can impact our visual memories, and incomplete, “alleged” stories can lead to conclusions that get sealed in memory as truths. In a 2015 study published by the University of California, Irvine, 33 percent of test subjects described watching nonexistent footage of news stories, including images of United Flight 93 on 9/11. The results make sense—air crashes are rich in visual horror, frequently depicted in films and on TV, and easy to imagine despite the absence of footage of that specific event from 2001.

This provisionally takes care of other “lesser” Mandela Effects like “Chic-fil-a” (it’s Chick-fil-A) and “Oscar Meyer” (it’s Oscar Mayer), but leaves more baffling ones unresolved, including celebrities who seemingly come back from the dead, or the people who report that New Zealand is located west of Australia rather than southeast. A recurring theme on r/MandelaEffect is the question of whether people are “really” experiencing the effect. New to the idea, it’s something even Østby picked up on.

“I found a web page showcasing different examples of Mandela Effects, and some of them are not the same as the Mandela Effect,” she said. “They’re people simply misremembering things. For instance, someone ‘remembered’ that Sri Lanka used to be somewhere other than where it is. That is just lack of geography. Failing to correct your own memory, or attributing it to some paranormal explanation with CERN, is disturbing.”

Certain words and phrases appear again and again in the Mandela Effect community: “Occam’s Razor,” “confabulation,” and the “many-worlds theory,” an idea taken from quantum mechanics, used to explain a common argument made by believers that they have skipped across dimensions, arriving somewhere familiar but not entirely the same. Those who disagree are said to be native to this “timeline,” having never known things to be different.

Rick and Morty, Black Mirror’s “Bandersnatch,” and more recently Netflix’s Russian Doll have popularized talk of many-worlds theory, but does the idea actually hold water in the scientific community? “Yes, there are definitely plenty of physicists who believe in the many-worlds interpretation of quantum mechanics,” Adam Becker, the author of What Is Real? The Unfinished Quest for the Meaning of Quantum Physics, told me. “There are also plenty of physicists who don’t, and even some physicists who believe that the many-worlds interpretation is unscientific nonsense. I’m in the middle: I think the many-worlds interpretation is a pretty reasonable scientific theory. But I’m not convinced it’s correct.”

The Mandela Effect interpretation of the many-worlds theory, however, wears thin when it comes to application. “It’s impossible to travel from one universe to another in the many-worlds interpretation of quantum mechanics, intentionally or otherwise,” Becker said. “There may be other universes, but nobody in this universe has ever been to those other universes.” A possible explanation for the effect, he added, lies in psychology, rather than in his own field of physics. “The brain is a remarkable and complex thing,” Becker said, “but it does not possess the capacity to physically hop between universes. Nor does the Large Hadron Collider have that power. To the best of our knowledge, nothing does. And in fact, other universes may not even exist.”

If those experiencing the effect have jumped between dimensions, what does that mean for the rest of us? That our lives are somehow less authentic? That we’re all programmed “sheeple,” or that we come from a replacement universe? This is what makes the Mandela Effect debate so intriguing: It branches into places the internet cannot reach, like the recesses of the human brain, or other dimensions, prompting theories that are unverifiable without mind-scanning technology, or perhaps a portal gun. It pits the human mind against the internet, but neither is infallible.

One thing that differentiates the Mandela Effect from conspiracy theory, however, is that it doesn’t claim to have found an answer. Instead, there are only more questions. “What makes this the biggest thing since sliced bread, for me at least, is all the possibilities,” 9_demon_bag said. “There’s so much potential, if you could just find the forces behind it.”