Okay, so the geek in me cannot resist the temptation ...
The most famous time-travel paradox is probably the Grandfather Paradox, but I think the scenario described in Robert Heinlein's By His Bootstraps is closer to what transpired in SPN 5.04. In this story, the present and future versions of the protagonist all interact with each other to produce the events, leading him to conclude these events must all exist in a closed temporal loop and are therefore non-causal.
There are many attempts to resolve these paradoxes. The multiverse (parallel universe) depicted in Trek is only one of the hypotheses on how to get around the problem, but I don't think SPN - with God and Devil - will use that particular solution.
There is a hypothesize that says the only possible timelines are those that are entirely self-consistent, i.e., a timeline where a man who travels back in time to kill his own grandpa (before the grandpa met the grandma) has probability of zero. In an important sense, this supports the concept of destiny, and I think it makes some sense for SPN to take this route.
The irony, to me, is that this second theory was proposed by a physicist. Who says one cannot prove the existence of God? ;)
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The most famous time-travel paradox is probably the Grandfather Paradox, but I think the scenario described in Robert Heinlein's By His Bootstraps is closer to what transpired in SPN 5.04. In this story, the present and future versions of the protagonist all interact with each other to produce the events, leading him to conclude these events must all exist in a closed temporal loop and are therefore non-causal.
There are many attempts to resolve these paradoxes. The multiverse (parallel universe) depicted in Trek is only one of the hypotheses on how to get around the problem, but I don't think SPN - with God and Devil - will use that particular solution.
There is a hypothesize that says the only possible timelines are those that are entirely self-consistent, i.e., a timeline where a man who travels back in time to kill his own grandpa (before the grandpa met the grandma) has probability of zero. In an important sense, this supports the concept of destiny, and I think it makes some sense for SPN to take this route.
The irony, to me, is that this second theory was proposed by a physicist. Who says one cannot prove the existence of God? ;)