In this and future time travel posts, I’m going to “think out loud” (e.g. do exactly what I always do on this blog) about some possible ways in which time travel might work, were it possible, and resulting implications.

When I think about time travel, I consider two potential timeline scenarios – immutable and mutable.  In the immutable scenario, there is only one timeline – that is, One True Time.  Imagine I go back in time and kill someone (like, e.g., my grandfather).  Since there is only one timeline, it must be true that I didn’t change anything – it was always the case that I arrived at that moment in time and killed that person. “How is this possible,” one might ask, since killing my own grandfather would seem rather paradoxical.  Well, in One True Time, if I did actually kill someone, it can’t have been my actual grandfather – events will have seemed to have conspired to make that true.

This version of time is fatalistic, in a similar sense to the biomachine-free-will argument: although people believe that they are making meaningful choices, they are really just acting out the programming, which in this case is the way Time “ought to be”.  An interesting conundrum with this sort of timeline is — who determined what the fixed timeline looked like, once time travelers were added to the mix (or what, or why, or at least how)?  The term “closed causal loop” stems from this conundrum: events that seem fated to happen don’t really have a cause, since their cause and their effect become blurred.  If I find a time machine, deconstruct it and make detailed instructions on how to build one, go back and give the plans to an inventor, and that inventor creates a time machine and leaves it for me to find, who created the time machine?

Immutable time is tidy, but not particularly interesting to me.  It can make for very dramatic science fiction – since conflicts can easily be railroaded via time travel to terrible, tragic conclusions (or beautiful, “serendipitous” conclusions), it works quite well.  But in terms of usefulness, I think it falls short.  Just as I don’t like considering lack of free will, I also don’t like considering predetermination of events.  Although… I suppose it’s still an open question as to whether events are predetermined BEFORE time travel is possible!