Station Clock (Credit: SusanMcM)
Use a number two pencil, draw a line on a piece of paper, erase it, and then draw a new line.
What do you see?
In most cases you see evidence that a first line was made, erased, and a new line was made. Essentially, the first line never completely goes away.
Backwards Time Travel
Your past is set in what can be called “Primary History.” Primary History is the original history; the original chain of events in your life that has become your past.
Science Fiction writers deal with time travel in different ways. The most popular time travel story has to be the Back to the Future trilogy.
Michael J. Fox stars as Marty McFly who travels back in time and almost changes his Primary History by preventing his parents from meeting. And actually he does change some aspects of his Primary History.
Backwards Time Travel Ain’t Possible
One thought is that backwards time travel is not possible, because it could erase Primary History. But if Primary History has already occurred, how could it be erased? If it is erased, will there still be evidence that it was erased?
McFly who travels back in time still has memories of his Primary History but when he returns back to his future he recognizes that his Primary History has changed: his parents are rich, Biff works for Marty’s dad, etc.
How could that be? Some would argue that time travel is impossible for this very reason–Primary History could be erased or altered.
Backwards Time Travel Creates an Alternate History
Another line of thought, which was used in the 2009 Star Trek movie, is that one can travel back in time but that creates a Secondary History–an alternate reality.
So once a person leaves Primary History s/he travels back into an Alternate History and cannot return to the Primary History. That person is stuck in the Alternate Reality, unless he or she leaves that History and travels to a Third History or another Alternate Reality.
In this case Spock Prime travels from the 24th century back in time to the 23rd century in an alternate reality. Spock Prime has disappeared from his Primary History.
Using that concept, consider Star Trek IV: The Voyage Home when the crew of the Enterprise travels back in time to find a humpback whale to bring back to the future to save Earth. The crew left Primary History, entered a Secondary History, got the whale, and traveled forward in time in Second History.
Who knows if either is possible?
Either way, Primary History remains protected. Or does it?
