The Mandella Effect

This seems to be a phenomenon, if you've been on the planet more than a few times around the sun you may remember certain things differently than what we are told.  Could just be a memeory glitch, or is it something else?  It all started with Nelson Mandella and some people believing he died in prison and never went on to become the president of South Africa.  I don't recall  him dying in prison, but there are some things that I am almost 100 percent sure were something different than what we are told now.  Is it possible we have slipped into an alternative universe?  If so, how did that happen?  What could have caused that?  Feel free to share your own experiences if you want.  tj2@up.net