
So, the wife has me watching Doctor Who. This is not an altogether bad thing. I have enjoyed David Tennant's portrayal of the Time Lord and despite the much maligned writing style of Russel T. Davies, have enjoyed many of the episodes as well. Granted I am not a Who fan per se, just a casual viewer. As such, I am not as invested in the Doctor and therefore less prone to attacks of fandom good or bad.
The adventures of the last of the Time Lords brings up several ideas about the nature of time. I won't go into great detail on the Doctor's treatment of time as I haven't the sufficient background as a fan to do so. Just the same, he will get the occasional mention. So, here is a brief overview of various time paradoxes.
THE GRANDFATHER PARADOX
This one blows my mind. Take into consideration that you are a traveler through time. Back several decades you encounter a woman. You develop a relationship, fall in love, possibly marry, and beget a child. That child grows older, marries, begets a child. That child grows older, becomes a traveler in time and meets the same woman you did.
In other words, you meet your grandmother and with her beget your father. You become your own grandfather. The rub of this paradox is that to be you qua you, that is to be as you have always been you would have had to meet your grandmother before ever being born. The very fact that you were born verifies the fact that you had already gone back in time. If you had not travelled through time, you would have never been born.
Mind blown.
The grandfather paradox was first introduced by fiction writer, Rene Barjavel, in his novel, The Imprudent Traveller. However, in his novel the time traveller kills his grandfather, thus negating the chance he will ever be born. The aspect of becoming one's own grandfather was addressed in an episode of Futurama.
The grandfather paradox appears to be inescapable and theoretically could lead to the destruction of the universe. However, if the traveller kills his grandfather and therefore is never born, then he could never go back in time to kill his grandfather, thus ensuring that he is born. The circle is viscious. Back to the Future confronts the issue of the traveller compromising his own existence. Marty McFly interferes with the meeting between his mother and father. To restore the timeline, he must get his mother and father to fall in love.
TIME LOCKED EVENTS
The nature of time tat Doctor Who seems to keep to is that of Nabikov's Self-Consistency Principle. In this sense time travel is possible provided the time traveller will not drastically alter the timeline. In other words, what happens in the time line is destined to happen. The time traveller may have certain room to move within the timeline provided key events that are "time locked" are not affected. In Waters of Mars, the Doctor comes to the first Mars colony. He realizes everyone there is destined to die. Having grown tired of so much loss, he attempts to save the colony. In the end, the leader of the colony knowing that she was destined to die, takes her own life. When the Doctor went to Pompeii, he instigated events that led up to the eruption of Vesuvius. As the eruption of Pompeii is an historical event, this suggests it has always been so and the Doctor's actions were permissible.
The problem with destiny is that it undermines freedom of choice. If events are destined to take place, then the efforts of man are pointless. What is meant to occur will occur nonetheless despite all efforts to the contrary.
ALTERNATE TIMELINES
Alternate timelines and parallel universes are favored by science-fiction and comic books. This allows the time traveller full reign over the timeline with little consequences. Any change to the timeline creates an alternate reality. Events taking place at and after the change splinter from the true timeline, that is, the time line from which the traveller originated. What If? comic book scenarios and various Star Trek episodes explore this aspect of time travel. The new Star Trek movie addresses this issue in depth, developing a time line far removed from that of the original series.
Other series such as Red Dwarf have fun with this concept, taking into account that there is a different timeline for each choice made by each individual. This suggests a near infinite amount of parallel universes. Rimmer meets his alternate self, who happens to be brave, charming, handsome, and confident. This extreme departure from Rimmer's jealousy, awkwardness, and self hatred stems from one event. In one timeline Rimmer is held back a year in school. As such, he applies himself, becoming a more upstanding person in the long run. The Jet Li vehicle, The One, suggests a more limited number of alternate timelines. Were one to kill off all the alternate versions of oneself, one would gain their power. This culminates in a showdown between two alternate selves with the equal amount of power absorbed from the destroyed selves.
The problem with alternate timelines is that they lack credibility. As they veer from the original time line, what happens seems to matter less and less as whatever the traveller does has no repercussions in his own time line. This may be why I didn't care much for the new Star Trek movie. That and I seem to be allergic to JJ Abrams.
THE BUTTERFLY EFFECT
The grandfather paradox is but example of the butterfly effect. The butterfly effect is a concept introduced in chaos theory that suggests, metaphorically, that the beating of a butterfly's wings in one part of the word can build over time to a hurricane on the other side of the globe. In short, any simple alteration to the timeline will incur drastic effects over time. A misspoken word, delayed travel, a moved object may instigate a series of misadventures leading up to a completely altered timeline.
The classic example is the tale of time traveller tourists observes dinosaurs. As long as they remain on the established path, the timeline is ensured. However, in trying to take a photo, one tourists steps off the path and crushes an insect. In returning to the present, he finds the alphabet and spoken language to have altered drastically. The events between are unclear, even illogical, suggesting that there is a fragile bond between all things that we not completely understand. Chaos theory suggests that events follow mathematical patterns. However, when a change occurs in the pattern, that change is compounded over time ultimately developing into a different result.
Left Turn in the Doctor Who series explores this aspect of time. Donna Noble is prevented from turning right, thus determining that she never meets the Doctor. As their paths never cross, events from that moment forward also take a different turn leading to the possible extinction of the human race. Only in returning to the moment of diversion can the original timeline be restored.
A Halloween Simpsons episode played with this concept, displaying different results for each different event that takes place back in time. Results varied from raining doughnuts to serpent tongued people.
RUBBER BAND EFFECT - TEMPORAL MODIFICATION NEGATION
If time can be viewed as a flowing river, then it's course can be diverted, blocked, slowed, or quickened, but the flow remains. Eventually the river will claim its original course. So, too, with time. At least that is what this theory suggests.
What ever alteration is made to the timeline is restored over time. The time traveller can do whatever in the past, even killing his own grandfather. However, when returned to his present timeline he will find that the actions he had taken have been negated as though he had never gone back in time. It is like pressing your palm down on a foal rubber mattress. At first it makes and impression. Eventually, though, the impression is restored to the point where no trace of a handprint remains.
Again there appears to be no repercussions, rendering this theory meaningless in a literary sense. What aims at nothing achieves nothing.
RESTRICTED TIMELINES
In a restricted timelines, any attempt to alter the timeline will either fail or ironically contribute to the historical effect. Let us say you go back in time to assassinate Adolf Hitler. As you take aim with your period rifle and fire, another assassin steps in the path of the bullet. You kill the would be assassin, in turn saving Hitler's life.
This fatalist attitude towards time travel makes for a good story. In HG Well's The Time Machine, our hero attempts to save the life of his lover. However, each attempt only leads to her demise in some other fashion. Murdered, drowned, struck by a cart. Similarly, in The Crow television series, Eric is given the opportunity to go back in time. He attempts to prevent the murder of his love only to find her dying by some other means. Having to continually witness the death of your love would become a living hell. Eventually one must accept the event and move on.
This basically is a more limited version of the time locked scenario.
AFTERTHOUGHT
So that is a brief sampling of various time paradoxes. A few more words on time is Nietsche's theory of eternal recurrence. Time is a spiral, like a coil or spring. Though it moves forward, it circles above past events. It follows the same valleys and peaks of decades past. In this sense, certain periods of war and peace repeat. Periods of wealth are followed by economic crashes. Classical art is followed by periods of romanticism.
In Eastern philosophy, time is regarded in less linear terms. Past, present, and future are regarded as coexisting side by side. Just as events in the present color the future, they also color the past. Look to how the discovery of Troy has changed how we look at the Iliad and the Odyssey. Events that have yet to take place, such as the birth of one's child, may influence who we are today. This more semiotic view of history is one of the major cultural gaps between the East and the West.