It’s called the “Mandela Effect” and a lot of people think it’s proof of an alternate universe.
The Mandela Effect is a theory put forth by writer and "paranormal consultant" Fiona Broome that shared false memories are in fact glimpses into parallel worlds with different timelines.
Broome says that the origin of her theory came out of a discussion of whether or not Nelson Mandela died in prison. Naturally, this happened backstage at Dragon*Con.
Many people who believe in the theory insist that the popular children's book series The Berenstain Bears was once known as The Berenstein Bears .
And that there are either 51 or 52 states in the United States, not 50.
Most of the people who believe this happen to be from other countries around the world.