What is the Mandela Effect and what causes it?

The Mandela Effect is a phenomenon in which a large group of people collectively misremember something. Writer Fiona Broome coined the term "Mandela effect" on her website of the same name.

"Nelson Mandela died in prison, long before his loss on December 5th, 2013," Broome wrote. "Many people-perhaps thousands-seem to believe that. ...I thought I remembered it clearly, complete with news clips of his funeral, the mourning in South Africa, some rioting in cities, and the heartfelt speech by his widow. Then, I found out he was still alive."

Broome began investigating the phenomenon, and she quickly discovered other popular misconceptions. For example, some people vehemently insist that they grew up reading about The Berenstein Bears (they're actually The Berenstain Bears). Some people insist that they watched actor Sinbad play a genie in the 1990s film Shazaam, but that film doesn't actually exist (although Shaquille O'Neal played a genie in the 1996 film Kazaam).

In most cases, the Mandela Effect is easily explained-people forget a few details when recounting some widely discussed cultural phenomenon, and a certain percentage of them share the same misconception.

However, there's an alternate explanation: At some point, we shifted into a parallel universe. People who suffer from the Mandela Effect aren't actually misremembering anything, they're just accurately remembering what life was like before two similar (but different) realities collided.

That's just one possibility. On Broome's site, readers post various supernatural explanations:

"Someone is changing the past for financial gain or altering the past and causing rifts in other areas by happenstance," one user wrote.

"It has occurred to me that we could have all died/passed on, and we are all in denial," another wrote. "Fiona [Broome], as a ghost catcher, lures us to the site and presides over this construct of simulated earth to ease us into truth and guide us in the proper direction."

Those are fairly compelling theories, but the simplest explanation usually makes the most sense-our memories are imperfect, and because our brains work similarly, some misconceptions are more likely than others.

Granted, that's not quite as fun as a theory involving ghost catchers and parallel universes, but it's the most likely explanation for the Mandela Effect.