In “The City on the Edge of Forever”, the crew of the Enterprise are faced with the task of intercepting a delusional Dr. McCoy from the war-bound, 1930’s America. By sending McCoy to the past, the concept of time travel is brought into question in the episode, and the method suggested by the show’s writers is highly questionable. When McCoy jumps through the portal, the future is instantly changed so that the Enterprise no longer exists. Therefore, in theory, the remaining voyagers from the Enterprise should have no longer been on the planet’s surface. One cannot clearly say whether or not the crew would exist in this altered future, but if there was no feasible way for them to have traveled to the planet, how could they have been there?
If this initial point is ignored and the episode continued unaltered, then Kirk and Spock would have traveled back in time to New York in the Great Depression. The pair would have arrived at a point a few days before McCoy’s arrival in order to intercept him, which is what happens in the episode. However, again in theory, this plan should have only worked if Spock and Kirk traveled in time and didn’t have any interactions with anyone or anything on Earth. This was obviously not the case in the episode and this duo had multiple interactions with several people. These interactions should have also altered the future just as McCoy saving Edith changed it. Therefore, even though the duo did catch McCoy and stop him from saving Edith, their presence should have had effects on people in New York: a homeless man ran off with one of McCoy’s devices that appeared to beam him somewhere, Spock and Kirk paid their tenant $2 a week for their room, and Jim Kirk’s relationship with Edith was actually the factor that inadvertently led to her death. Given all of these occurrences, why was it implied that the world returned to its original state? Shouldn’t at least one of the many changes affected someone’s life in a way that it wasn’t affected before and therefore changed Kirk’s present?
I’d suggest that this approach to time travel is slightly flawed, but highly convenient. By having a relatively simple solution to an unimaginably complex problem, “The City on the Edge of Forever” was able to create a conflict, show some rising action, climax at a dramatic point, and then allow a little bit of time for falling action without making any lasting changes to the franchise’s storyline. Did the writers create this scheme for time travel because they thought it to be the most logical or simply because it was the most convenient to squeeze into 50 minutes? While only they truly know, what do you think?