å Kurt Sanders: Time Travel Paradox

Sunday, February 22, 2009

Time Travel Paradox

Time travel is a immensely fascinating topic and can be discussed with friends & family for an infinite amount of time. For purposes of this blog, I will introduce "Time Branches"

Suppose a person travels to a historical time before they were born and breaks the event that led to the traveler's birth. This problem has been commonly explored by asking 'What if one kills their own father's mother before she first conceived your father?' The apparent paradox is then of a logical sort:
  • X forces NOT X and NOT X forces X.
If one kills their father's mother then one would not be born, which in turn would bring it about that one not travel into the past, thus one would not kill ones' father's mother, thus one would be born causing one to again travel into the past to kill ones' father's mother....
  • Thus the "Ad Infinitum" endless loop.
The presupposition of almost all time travel stories is that each point along a time line is in some sense existent now, even the future points. This provides a conceptual basis for allowing us to visit a time point in the same way that we might visit a space point in ordinary experience. Einstein may have reinforced our comfort with this view by taking seriously the notion of time as another dimension very much like the spatial dimensions we are already familiar with.

Some stories entertain the notion that you can go back and change things, but not those things that would lead to paradox. I would like to put forth the view that there is something wrong with all of these approaches and that the only view which is successful at resolving the paradox is an alternate universe theory of time travel which we shall explore momentarily. Such a view was expressed in "The Terminator" in which a character from the "future" confesses that maybe he just comes from a "possible future " not the actual future of this time.

When a time travel event occurs, it is helpful to see that it may be one of two kinds. Take, for instance, a "traveling" from time point c to time point b, where c is later than b. Either we are sending an object to a time and place where it already was and it is the same object in every respect as that object in that time and place or we are sending it to a place that it wasn't or at least wasn't in that exact state. Let us consider the second possibility first.

Supposing that the object wasn't at b but we intend to send it there anyway. If we are successful then we have created a contradiction, for it becomes clear that when the time travel event occurs it becomes true that the object was at time point b and yet it was false that the object was at b. This is an impossibility if we take any standard linear view of time. The most minimal means to accommodate this contradiction is to allow a timeline where the statement that the object exists at b is true and another timeline where the statement that the object exists there is false (the 'original' timeline.). In other words a timeline branching event has occurred. Any story that holds that the object was not on the timeline and now it is, is minimally committed to this branching universe concept. See Figure A...


Nancy Sanders said...

I don't believe in time travel and I wish you and Kj didn't either.

Nancy Sanders said...

Okay I read your blog and it is like reading a software manual to me. Let me say this about time travel, it would be a nice concept if one could go back in time and view someone that is no longer alive, as an example, I would enjoy seeing my mother again. The only way I could ever consider the notion of time travel is providing the future or the past can not be altered only visited.