Our memory is imperfect. We can recall some things differently from how they happened, even remember things that never happened. Sometimes, however, larger groups of people can misremember something the same way.
Psychologists call these collective false memories -- or just 'false memories' for individuals. It's also commonly known as the 'Mandela effect', so christened by "paranormal consultant" Fiona Broome around 2010.
Needless to say, they have enough of a 'spooky factor' to capture public interest. Examples of and explanations for the false memories abound on the internet. It's even been proposed that those people remember alternate universes, which they've lived in before somehow switching to our own.
Definitely an interesting story. But the origin of this phenomenon is more likely produced by an interplay between how our memories are formed, how they are stored, and our innate drive to fit in with the group.
Table of contents
How it got the name
In 2009, Broome attended a conference and talked with other people about how she remembered Nelson Mandela dying in a South African prison in the 1980s. They seemed to agree with her.
His death in the 1980s makes Mandela's term as President of South Africa between 1994 and 1999 all the more impressive.
Broome eventually realized her mistake and shared the story with her friends for a laugh, but soon realized that they too misremembered the dates. They even shared having memories of news coverage of Mandela's death and a speech by his widow. Others she asked said they remembered his death in the 80's as well.
Encouraged by her book publisher, Broome would launch a website to discuss this Mandela Effect and other similar incidents. Presumably of the paranormal kind.
What we know about it so far
Whether Mrs. Broome was being genuine or just working on establishing her new audience, we can't know. But she is right in pointing out that collective false memories are a real phenomenon.
If you're a fan of sci-fi or movies, you probably know this phrase: "___, I am your father". It's one of Darth Vader's lines from The Empire Strikes Back and one of the most iconic phrases to come out of the cinema. But it's not how you remember it; it's actually "No, I am your father" (Youtube link).
The line stuck around as "Luke, I am your father" in public memory. It's not clear exactly why. Vader's previous line starts with "Luke", so people may have conflated the two. It's arguably cooler than the original quote -- maybe someone in marketing figured that out and tweaked it for appeal.
There are a few factors that could lead to the creation of such memories. First of all is suggestibility, our inclination to take information from others as true. Memory can shift to better suit information we're presented with, especially if we're repeatedly exposed to it. Secondly, the way our memories are encoded and recalled can alter them over time, either as far as the contents of that memory go or its source (misattribution of memory).
Memory formation and recall
Our memories reside in groups of neurons. Their position in our brains, the little network where this memory is physically housed, is that memory's 'engram'. As we grow and learn, our experience helps create a framework where engrams of similar memories are housed close to each other -- this structure is the 'schema'.
There are a few key steps memories go through that can disrupt them, leading to false memories. First, information must coalesce into short-term memory. Our perception of events, along with phenomena such as priming will shape what we remember.
This data must then get transcribed into long-term memory as we sleep. It can suffer a change until it is thus imprinted as it makes its way through the brain's different storage sites -- especially under states of heightened emotion.
Furthermore, whenever we access and recall a memory, it temporarily becomes unstable in the brain while it's being read. New connections form between the neurons. It does re-consolidate afterward, and repetition leads to better memories due to this process. However, there's also a chance something can go wrong and the memory changes as its engram activates.
If two memories are close together in the brain and activated at the same time, they can even start blending together -- this could be why we remember Vader's phrase the way we do.
Psychological priming is a process through which our perception of an event is influenced by the events or stimuli leading up to it. This process largely works in the subconscious and can alter our memories to fit in with our priming. It largely overlaps with suggestibility.
Asking someone "how fast the car was speeding?" can prime them to remember a higher value than "what speed was the car moving with?".
Eyewitness testimonies are notoriously unreliable because of phenomena such as priming. Memory can change -- without a witness being aware of this -- to suit new information, the questions they receive and their wording, or simply due to their emotional state at the time and while testifying.
Our brains will fill in the gaps in our information to make it make sense in a process called confabulation. Through this, we can remember details that never happened because they help our memory make better sense. Combined with our inborn desire to be part of the group and/or priming, our memories can thus shift to suit the collective narrative we're presented. Any new information we receive that's tied to the memory also alters it to some extent.
Memory inaccuracy can also come from "source monitoring errors", when people fail to distinguish between real and imagined events. And, naturally, how old a memory is, and how often we access it, further impacts its quality.
Our memories are a large part of who we are. It can be quite scary to understand that they change, without our knowledge, often to a great extent. Or, even worse, that whole groups of people can live with the same false memory.
Human memory isn't perfect, but it was never meant to be perfect. It was meant to keep us alive. We're still around, so it seems to be doing its job.
Modern life places very different pressures on our minds and bodies than the environments where they evolved. In a way, the Mandela effect is a by-product of our brains' efforts to be more efficient. Keeping every memory ever in perfect shape isn't efficient, or particularly useful. If something is important then you'll probably interact with and think about it repeatedly, and the memory will always be refreshed and reinforced in your brain. That's why calendars are helpful.
You don't need to remember your fridge perfectly the first time you see it, just roughly where it is. And your brains know that. The Mandela effect lives in the memories of things we don't check often. Something we kind of half-heard someone say once, maybe. A line in a movie 40 years ago.
Through a combination of our innate drive to fit in with the pack, the way we prime each other when we interact, and our brain's tendency to fill in memories, false memories can spread among a group -- as long as nobody there bothers to check on Wikipedia.