'Fringe' has really been delivering the goods this season and a recent episode - "White Tulip" - was a fascinating look at time travel; made even better with the guest performance by Peter Weller as Alistair Peck, an astrophysicist specializing in bio-temporal travel. Basically, he was a home-grown quantum leaper.
But as good as the episode was, there was still a problem with its use of time travel.
Here's what happened: back in 2009, Peck's fiancee died in a horrible car accident. And since then Professor Peck worked on realizing his time travel theories so that he could go back to the accident. (We were led to believe that he wanted to change history by saving her life.) But every time he tried, Peck could only go back to a moment on board a "Mass Transit" train. (Not sure on the actual name of the train system, but I think it was a commuter service like a lower level Amtrak, more like NJ Transit.)
This ended up killing everybody in that train car - his "quantum leap" needed to drain all of the energy in the immediate area upon Peck's arrival and that included the bio-electrical energy in human bodies. With an assist by Walter Bishop, Peck was finally able to get back to before the accident - in time to join his fiancee in the car before the crash and so he died with her.
But here's the thing - what happened to the Alistair Peck of 2009?
On that date, at the time of the crash, Peck was standing in a field looking at a hot-air balloon. He chose to go back to that field so that the energy drain would only kill the surrounding vegetation - the grass and the trees. (No idea where the guy was who was supposed to be tending that hot-air balloon.)
But if he was already there, he would have been killed as well. And that would have negated his whole future, which would have rewritten history or created a parallel timeline. By rights, Peck should have faded from existence as soon as he reached the past if this happened.
Now, let's suppose the 2009 Peck didn't reach that field before the 2010 Peck arrived from the future. He was a genius so it wouldn't be long before he realized that he'd have to change his identity while he continued his research. But the plan of action would alter history as well since he no longer would be following his original timeline. In the 'Doctor Who' episode "The Idiot's Lantern", the Doctor and Rose Tyler were enjoying the neighborhood block party celebration of Queen Elizabeth II's coronation on June 2, 1953 at the end of their current adventure....
Out on the street, 50's music is playing, people are out on the street dancing and talking. Trestle tables line the centre of the road covered in pastries, cakes, drinks, etc. The Doctor and Rose walk down the street.
We could go down the mall, join in with the crowd.
Nah, that's just pomp and circumstance.
This is history right here.
The domestic approach.
[courtesy of the Doctor Who (2005+) Transcripts site]
History isn't just the big events; it's the result of the small interactions we have with other ordinary people. Change just one of those encounters, and history could be affected. It brings to mind that classic example of Chaos Theory - kill a butterfly in the primordial past and you could alter the future timeline.
So if 2009 Peck had to abandon his previous life, that means he could no longer have any interaction with the people he should have met in his previously played-out future - family members, business associates, friends, neighbors, grocery clerks, his doctor and dentist, etc. And those lost encounters would remove the ripple effects which could have led to other "historical" events. Small they may have been, but ultimately they could have led to something of greater impact.
We could use such an alteration to the timeline to splain away any discrepancy in a TV show episode that took place between May 18, 2009, and whenever "White Tulip" took place. (That's a project I have not yet looked into. I was hoping it could be used to wipe out the appearances of Governor Shalvoy from 'Law & Order', but Tom Everett Scott began playing that role in 2008.) So if you think of anything that causes a discrepancy in a TV show after May 19, 2009 (in the Toobworld timeline), let me know. Maybe we can bring that show back into the fold using this rewrite of history.