I guess I should premise this post with the disclaimer that I'm not a time traveler and have no first hand knowledge of how these things work. I'm also not a theoretical physicist who spends their entire life studying these things. But I have taken a few advanced physics courses during the course of getting my college degree and I have read a number of books written by actual theoretical physicists. I would like to think I can discuss this topic with some sense of knowing what I'm talking about and not completely spewing hot air.
The other day a friend of mine and I were talking the merits of time travel in the movies, how it's depicted and which movie does it best. The main movie he concentrated on was the
Terminator series (movies + television). After thinking on it for a bit I thought I'd post this today. This is mainly the result of my musings, based on my understanding of string theory and the dimensionality of the universe. Before I really get into it though, here's a short video I found based on
a book I read recently that attempts to explain the dimensionality in the universe.
Ok, you're still reading after watching that. Good. Think of our timeline as a single line. Every event in our past is defined. It's happened. There's no changing it. Our future timeline has an infinite number of possibilities. Every event, choice or decision that is made in our future could send us down any number of paths. Every distinct path is its own alternate universe, sharing commonalities with other universes only prior to the events that split them.

In regards to the Terminator series, the more I think about it, the more and more I see that they really didn't have a clue what they were doing in regards to time travel. In the original
Terminator movie,
John Connor sends a man back in time to 1984 to stop a Terminator from killing his own mother before he is born. The fact that John Connor exists in 2029 is evidence enough that in his particular timeline, his mother didn't die. He was in fact born. As soon as the Terminator goes back in time, that timeline is changed at the point he arrives. From that point in time, that timeline is now a distinct, different universe than the one the Terminator left. Nothing that happens there can ever cause that timeline to coincide with the original timeline, because in that timeline, no Terminator existed in 1984. Also, when Kyle Reese is sent back, he can never end up in the same universe the Terminator ended up in, because his time line he is traveling back in, is one in which the Terminator never existed in 1984.
From the perspective of the original John Connor, a Terminator and Kyle Reese both went back in time and nothing changed. Nothing in his universe is affected because their presence in the past branched the timeline down a different path than the one that was his past. Essentially, this means that time travel for the sake of changing your past, in your universe, is impossible. Yes, you could go back to cause changes, but those changes would only present themselves in an alternate universe separate from the one you left. Also, traveling 'back to the future' from a time in the past you visited, would never return you to the universe you left. Instead, it would return you to a possible future of that timeline you created by your presence in the past.
Essentially then, time travel is pointless as a method of changing the present by traveling to the past because you will never affect the current timeline you're in. From the perspective of being the time traveler yourself, you can use time travel to move into a new alternate universe and improve (or degrade) your situation. But from the perspective of staying in your original universe and sending someone else back in time to change things for you, it's totally pointless. Nothing would ever change. In regard to television and movies depicting time travel (or dimension travel, if you will), the only show I think that even came close to grasping this concept was the show
Sliders, where the main character built a device to travel between these infinite parallel universes, neither forward nor backwards in time though. I guess that's why I actually enjoyed watching that show.
Labels: General Geekiness, Random