The Grandfather Paradox and other Paradoxen

There is a thing in time travel theory called the Grandfather Paradox. It goes like this: A time traveler goes back in time and kills his grandfather as a baby. Killing his grandfather means that his father will never be born meaning the time traveler will never be born. The paradox being that if he wasn't born, then he couldn't go back in time and kill his grandfather? Thus, a paradox arises of if he couldn't be, then how could he?

But I don't think it's a paradox. It's just a jerk thing to do to a baby. The time traveler merely created another universe where he will never exist. That's okay because he was a jerk anyway. There's an infinite number of those universes. The time traveler's universe, where he was born, must still exist as the time traveler also exists. But still a jerk thing to do to a baby.

If Retrospective Determinism has an evil twin, it's the Grandfather Paradox. Retrospective Determinism states that because it happened, it was always going to happen. The Grandfather Paradox states how did it happen if it was never going to happen? Both are very confusing and also found a lot in the Back to the Future film series. The creators merely glazed over such occurrences (or used them out of context) to weave their story. All this does is half open and half shut doors on the space/time continuum.

In fact, the entire first part of the series is one big Grandfather Paradox. Marty must get his parents together so that he has a future. Marty, obviously the time traveler, has metaphorically killed the event that leads to his conception and birth. Therefore he will cease to exist. But if he ceases to exist, how will he be able to go back in time to stop the event? But he did. What? Boom! Paradox in yo face!

Then, in Part 2 of the series, Old Biff goes back in time to give Biff the almanac. The Grandfather Paradox here being: how can Old Biff still be Old Biff if giving young Biff the almanac changes the future? Young Biff now lives in a universe where he gains rapid wealth and power. There is, at the least, a 1985 in this universe that Old Biff creates. Assuming there is also a 2015, this is where Old Biff would arrive when he time traveled to this year. But...this means that there is no longer an originating 2015 from whence Old Biff had original access to the DeLorean and the almanac. Only the alternative 2015 (2015A) is the current year now. Any point in the past is the history of this universe. One point in the past is Old Biff getting in the DeLorean, but that doesn't happen in this universe. So neither would Old Biff giving the young Biff the almanac. Thus it wouldn't create this universe. But it did. What? Boom! Paradox in yo face again!

Doc Brown describes the strange solutions of such paradoxes as a "ripple effect." The effect of actions made creates a ripple of changes through time. Doc doesn't seem to believe or acknowledge the existence of the multiverse. He seems to believe that it is one universe with different timelines. If an event is altered, it creates a new timeline. It does not create a new universe. Some things, like Marty's birth in Part 1, simply do not happen. That timeline no longer exists. The physics of this hypothesis are experienced by Marty as he begins to disappear while playing guitar. Other affects of altered pasts lead me to believe in the multiverse. Too many paradoxes result from a single universe/multiple timelines logic. Most paradoxes in Back to the Future can be solved with the multiple universe/single timeline logic.

Aside from the two mentioned above, here are a couple more paradoxes the Back to the Future film series leaves in its wake:

In Part 2, Doc and Marty go to the year 2015 to stop Marty Jr. from going to jail. Having accomplished this task, there would be no reason for Doc to go back in time to get Marty to stop his son, Marty Jr., from going to jail. But if Doc never brings Marty to 2015, how could they stop the events that lead to Marty Jr.'s arrest?

In Part 2, Jennifer goes to the home of Old Marty and Old Jennifer. They seem to have no idea that they once traveled forward in time to this day in this year (October 21, 2015.) Wouldn't Old Jennifer remember all the memories that young Jennifer is making?

In Part 3, Marty goes back in time to 1885 to stop Doc from getting shot. He prevents Doc from getting shot, meaning there should be no reason for Marty to go back in time if Doc never gets shot. But if Marty doesn't go to 1885 to stop Doc's shooting, Doc gets shot anyway.

It's also worth noting that on November 12, 1955, young Doc and old Doc meet briefly. Old Doc offers to correct young Doc with a 3/4 wrench instead of a 5/8. Although not a paradox, there was a pair o' Doc's.

Thank you.