"The ‘Mandela Effect’ is a curious, mysterious and fascinating phenomenon whose term was coined by Fiona Broome. It is the where masses of people clearly recall either a specific event in history or the name or spelling of an item as being a particular way, however all public historical records and other people contradict what you remember as being a fact.
It is like what all these people remember never actually happened, yet you are so sure that it did and you have clear memories of it. This leaves the people experiencing the anomalies as feeling completely perplexed, puzzled and even weirded out, like reality has changed.
What is interesting about this is that it is not just the odd person. In some cases it is thousands of people who share the same memory that contrasts current historical data or timelines.
There are literally people all over the world who are not related or connected to each other at all, that are collectively recalling the exact same historical information – yet all written information whether in books , newspapers or online sources of information contradict this. So it is not a sole, subjective experience – making it harder to disprove and debunk."
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http://www.nataliakuna.com/the-mandela-effect--alternate-universes.html