The concept of time travel has been used in fiction forever, but parallel time probably is a newer idea.
I did some research at one time into Borges' concept of timelines branching off in alternate directions in his 1948 "The Garden of Forking Paths," a story I have been studying (in Spanish and English) since I first encountered it in college Spanish. I'm not sure if that's exactly the same idea, but it would seem to be a related concept.
On January 7, 2009, MagnusTrask posted:
"As far as Trek, in the early days it was very much based on the kinds of ideas in printed science-fiction, and yes, they thought that at least some of these inventions would happen one day. They just had little way of knowing which ones. They put a lot of thought into what future technology might actually be like. That's one thing that made Trek so special. Networks just wanted "entertainment".... "
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What I was thinking of though was a more detailed post or article that may have talked about a specific author, story, and publication.
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On September 08, 2010, MagnusTrask wrote:
"The "Many Worlds" idea of human choices actually creating splinter-realities is not something that would have been in the minds of DS writers then, or anyone making alternate-reality episodes of any other program. The idea probably did not exist yet. It didn't make its way into TV till the '90s.
DS confuses things a bit by referring to PT 1970 as "another time" (to sound more romantic, even though it's the same time), and this can lead to both PT1970 and RT1995 being thought of as "alternate timelines" in some vaguely similar way. A "timeline" is the one and only way history has gone. The thing is, with time travel you can change that one and only way history has ever gone, so that that one single course of history is a different one "now"!
While PT is an alternate reality to ours, though, 1995 is our future. When we see 1995, it is the one and only timeline. Unless one wants to introduce the very alien and (I think) disruptive, modern "Many Worlds" idea that the writers didn't have in mind, Gerard might think he can safely let Barnjulia go, but he's wrong. [spoiler]Once they (somehow) acheive all their objectives, the one and only timeline that exists changes, so that Gerard's ghost's 1995 never happened. Not only does Gerard not proceed into an alternate 1995, 1996, etc, still in control of Collinwood as a ghost, but the 1995 we saw has never happened, not in an alternate "timeline" or in any kind of reality.
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Given the Borges story first published back in 1948, I don't know that I would agree entirely with MagnusTrask when he wrote:
"The "Many Worlds" idea of human choices actually creating splinter-realities is not something that would have been in the minds of DS writers then, or anyone making alternate-reality episodes of any other program. The idea probably did not exist yet. It didn't make its way into TV till the '90s."
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Here are some quotations from the Yates translation of Borges' story:
"In all fictional works, each time a man is confronted with several alternatives, he chooses one and eliminates the others; in the fiction of Ts'ui Pên, he chooses-- simultaneously--all of them. He creates, in this way, diverse futures, diverse times which themselves also proliferate and fork. . . . In the work of Ts'ui Pên, all possible outcomes occur; each one is the point of departure for other forkings. Sometimes, the paths of this labyrinth converge: for example, you arrive at this house, but in one of the possible pasts you are my enemy, in another, my friend."
and:
"He believed in an infinite series of times, in a growing, dizzying net of divergent, convergent and parallel times. This network of times which approached one another, forked, broke off, or were unaware of one another for centuries, embraces all possibilities of time. We do not exist in the majority of these times; in some you exist, and not I; in others I, and not you; in others, both of us. In the present one, which a favorable fate has granted me, you have arrived at my house; in another, while crossing the garden, you found me dead; in still another, I utter these same words, but I am a mistake, a ghost."
[Jorge Luis Borges, "The Garden of Forking Paths," translated by Donald Yates]