I was watching Terminator: Salvation this weekend and it got me thinking about some time travel issues that might arise as a result of Skynet's mission to kill John Connor. Basically, Skynet has tried to kill John Connor on multiple occasions during various stages of his life. In the first Terminator, they actually tried to kill his mother, Sarah, to prevent him from being born. This led to John sending Kyle Reese back in time to protect his mom, which actually resulted in his conception, since Kyle Reese ended up being his father. Another result of this original time travel venture was the Terminator that was sent back by Skynet. At the end of the film, Cyberdine Systems ends up with the Terminator arm and microchip, which leads them to develop the technology that would become Skynet. Therefore, it is imperative that John Connor of the future be allowed to send Kyle Reese to the past forcing Skynet to send the Terminator after it. If that doesn't happen then Skynet may never exist. So the attempts to kill John Connor at later times in his life could in fact be destroying Skynet's entire existence. Unless of course, the sentiment that was introduced in Terminator 3 was to be believed, that you can't change the future, you can only postpone. By that theory, Skynet would eventually be created and the discovery of the arm and microchip only hastened that creation.
Or you could subscribe to the Back to the Future theory of alternate futures. If you remember from Back to the Future II, old Biff went back to the past to give young Biff the Sports Almanac causing an alternate future to be created in which Biff is rich and murders George McFly. In this alternate future old Biff would not have traveled back to 1955 to give young Biff the almanac creating the question of how this future could ever exist if that event never happens. The same could be said about Connor sending Reese to the past leading to Skynet's creation. If Connor is killed before this happens, how does Skynet get created? But if an alternate future is created with Connor's death after Reese has been sent to the past, then that has already happened. It's enough to make your head spin.
If you're still confused after reading this, I apologize, but I'm convinced that there is no clear way to explain this. If anybody else has thoughts, please share. Until then, be wary of time travel, for you may end up in an alternate future.