Disclaimer: I just recently started researching "The Mandela Effect" so I might have something wrong in this post. If I do let me know in the comments below.
What is the Mandela Effect?
Simply put it is the Past Changing. Some believe that the past is "not fixed" and can change "after the fact". Some believe it is Alternate Dimensions bleeding over into ours causing the past to change and differ from our "recollections". A popular Mandela Effect (IMO) is the "Berenstain Bears" that pretty much the entire damn planet remembers as "Berenstein Bears".
Time Travel Causing the Mandela Effect?
For a minute let's assume that at some point in Humanities future the ability to Travel to any point in the Past is developed. Just the shear presence of someone or something Out-Of-Time can and most likely will cause small changes in the Past. For example: let's say I travel back to the year 5,000 BC and am standing in the middle of a field in Kansas for 5 minutes. My presence in that field will change the Wind pattern (ever so slightly), birds, animals, butterflies, etc. will alter their course to avoid me. Those minute changes could have major effects on the future from that point on, my past. 7,000 years later when I return to 2018 everything seems more or less right, but when I really start looking I discover that The Woolly Mammoth never went extinct, Butterflies vanished 6,000 years earlier and Native American's kicked Europeans Ass and forced the young United States of America to be a more tolerant and accepting country where Slavery never happened. Now what if I only went back in time to Watch the "Gettysburg Address" and I was standing between Abraham Lincoln and John Wilkes Booth who was in the audience to "stalk" Lincoln. Because I was there, in the way, John Wilkes Booth "listened" and "heard" things he wouldn't have heard otherwise, or understood things differently and as a result never Assassinated Lincoln? Or what if my presence pissed off John Wilkes Booth and he took out his frustrations by Killing Lincoln?
Is there another Explanation for the Mandela Effect?
Well here are a couple I can think of:
1.) Alternate Dimensions bleeding into each other, as mentioned earlier!
2.) Time Travel, as mentioned earlier!
3.) Time is not fixed or linear but instead is fluid and circular.....meaning that time overlaps itself in a giant loop and as one point in time touches another point in time anything happening in the present can alter the past. Who remembers the Spirograph from the 1970's. It was a brilliantly simple tool that consisted of plastic outer rings and smaller inner pieces that you put a pencil in and moved around to draw intricate patterns, that all overlapped and touched, sometimes in millions of places. Think of Time like one of those drawings and everywhere the lines touch is where the past and future cross paths.
