Time Travel as a concept in science fiction films

The film, Terminator Salvation while being an action film has a central theme in it-that of time travel. Many films, especially Hollywood films had explored the concept of time travel. Good ones that really put some thoughts on the concept are "The Terminator" series, the "Back To The Future" trilogy, "12 Monkeys" and the "Star Trek" series and films. The bad ones are Van Damme's "Time Cop", the remake of "Planet of the Apes" (the only thing that makes it passable is perhaps Scarlett Johansson); and Jet Li's "The One" with its non-sensical depiction of multiple universes (multiverse or many parallel universe).

The concept of time travel in the Terminator's film 'universe' is different than the ones in the Back To The Future's (bttf) film universe.

The first film of the 'Back to the Future' trilogy does bring back some fond memories. First shown in the year 1985. i remember it was the last day of school just before the school holiday. A group of classmates, quite a large group of us, went to watch the film. Those days, there were no cineplexes. There was only purpose-built one-screen cinema, and the screen was huge, much larger than the current cineplex's screen. It was the first and last time that a large group of us sat and watch a film together. We had a really good time, sharing jokes and laughter before the show. The film was so good that-it was funny and thought-provoking at the same time. And the song which played during the end-rolls was jsut fitting-Huey Lewis and The News "The Power of Love". After it was over, we talked about it and all of us went home with a smile. I never forgot those moments after all these years.

The concept used in the film is just one of many postulated in science fiction about time travel. It is the "ripple effect" in a single timeline (or space-time continuum) universe. No multiple universes or parallel universe. Multiple alternate realities existing at the same time just does not seem plausible although it may be possible. Incidentally, the quite watchable tv series "Sliders" uses the parallel universe theory in a 'responsible' way.

Time travel brings with it certain contradiction in logical sense or the universal concept of 'cause and effect'. The most common is what is term the "Grandfather (or Grandmother) Paradox". It is how a time traveller's action when travelling back in time alters the time traveller's future creating a paradox. A violation of the most fundamental law of nature - law of cause and effect.

The Grandfather paradox could be shown using a Mobius Strip.


Original link here

A time traveller returns to a time before the time traveller's mother is born and accidently (or purposely) caused the death of his grandmother, thereby creating a paradox. If the time traveller killed his grandmother then he would not be born, therefore he cannot travel back in time and kill his grandmother. So his grandmother is still alive and accordingly he would be born. If he was born, then he could travel back in time and kill his grandmother. Cause and effect breakdown in a paradox, which does not make logical sense. A later event could not affect an earlier event. Causality, simple law of cause and effect. Events could only progress forward in time. If events that happened in the past did not include the time traveler killing his grandmother, then he could not possibly create another event in the past that does. The laws of physics would prevent this from happening. This makes sense looking from an external view of time. An observer point of view. Consistency of physics and logic remains.

Strangely, looking at the event from a personal time view, the view of the time traveller's perspective, it seems posible and even consistent. The time travller travels back to the past and killed his grandmother. If the time traveller succeeds in killing his grandmother, then at that moment his universe "branch" into another universe in which he is still around. And the story of his life goes on from there. He's still the same person but probably don't have an identity in this 'new' world. Multiple universe. A parallel universe existing at the same time as the "original" universe from where the time traveller came.

Then, there is the causal loop or predestination paradox. A causal loop is "a chain of causes that closes back on itself. Event A causes event B, which causes event C,...which causes X, whcih causes A, which causes B and so on ad infinitum." In a loop. There's no certain cause which can be pin-pointed to an effect.

An example of a causal loop story:

A: Jennifer (teenager) is visited in her bedroom by Jennifer (old woman)
B: teenage and old Jennifer talk about tennis.
C1: teenage Jennifer says goodbye. C2: old Jennifer says goodbye.
D1: teenage Jennifer matures and has a succesful tennis career. D2: old Jennifer returns to her original time.
E: Jennifer obtains a time machine
F: Jennifer uses the time machine to travel to the past.
A: Jennifer (teenager) is visited in her bedroom by Jennifer (old woman)

"At event C, the story splits into C1 and C2. The causal loop continues along C1. At C2, the worldline of Jennifer continues outside the causal loop events. Events along the causal loop have no beginning and no end." There's causation and reverse causation at play.
(source: Time Travel Encyclopedia).

This paradox was chillingly and effectively used in the excellent film "12 Monkeys" with Bruce Willis and Brad Pitt.

But according to Prof.Stephen Hawking, again the laws of physics would prevent this from happening. "If a time traveller could travel to the past, whether or not the past included their younger self, they are prevented from interacting with the events of the past."

Most time travel stories are based on logical consistency, especially Hollywood films. Single time-line films like bttf contains a lot of paradoxes that is difficult to grasp. But the time travel concepts used in a good film like bttf (part 1) somehow still manage to make sense with minimal inconsistency. Films that alludes to multiple timelines (parallel world/universe) like the new Star Trek, are easier to follow. The new Terminator film could possibly go along this parallel universe route or maybe the "time-loop" direction as hinted by its current director McG (that is, if he continues to direct the remaining films in this franchise in the future, which depends on the franchise still having a future).

An entertaining film about time travel should not have too many illogical paradoxes such as those mentioned. Or should be able to explain away in the plot or keep these ambiguous for the general audience not to notice (and debate among themselves, for those who are too free with their time!). Majority of film-goers care more for the consistency of logic of time-travel films otherwise they would be seen as an insult on their intelligence. And perhaps most important the entertainment value of these films. The other type of time-travel film concerned itself more with known laws of physics. They're often difficult to understand but thought-provoking. The bttf, Terminator films are the former types. Fun to watch and not too taxing on the mind. The latter category are films like "12 Monkeys" and "Primer".

As Doc Brown would say in the bttf films, "The future isn't written. Your future is whatever you make it". So there.

HUEY LEWIS &THE NEWS : POWER OF LOVE

The "Back to the Future" time travel concept and its paradoxes explained:
Back to the Future (Part 1)
Back to the Future (Part 2)
Back to the Future (Part 3)