This article is from the The Terminator FAQ, by Karsten A. Loepelmann firstname.lastname@example.org with numerous contributions by others.
Naturally, any theory of time travel is just that: a theory. For the purposes
of this FAQ, the best we can do is try to apply one or more of these
while still maintaining internal consistency with the info presented in the
films. There are many theories of time travel in science fiction and comics.
However, most discussions of time travel focus on two theories of
physics: classic Newtonian and quantum mechanical physics. For a good
introduction to the application of these theories to time travel, see the
article, "The quantum physics of time travel" in the March, 1994 issue of
The classical theory states that there is one existence, and thus a single
timeline. According to this view, changing an event in the past could
theoretically retroactively change history from the time traveler's POV. This
theory is plagued by problems of "temporal paradoxes". For example, what
happens if you go back in time and prevent your parents from meeting?
(According to the movie "Back to the Future", you will "fade from
The quantum view is that time travel is possible along distortions in
space-time called closed timelike curves; also, reality exists as a
of infinite possibilities. Thus, if you travel back in time and prevent your
parents from meeting, there's no paradox. Your parents still meet and
you in the timeline you came from (after all, you must have come from
somewhere!). However, a "version" of you will *not* be born in the timeline
you traveled to.
Brian Christopher Weaver <email@example.com> writes:
The 'many-universes' interpretation of quantum mechanics solves a lot of
time travel paradoxes. A time traveler can make "any" change in the past
he/she/it wants to without endangering their existence because they came
from a "different" universe whose timeline is untouched by their meddling.
Therefore, there really is no paradox in the Terminator movies. The
Terminators and Kyle Reese came from a universe where the war actually
occurred, but by the end of T2 a universe had been created where John and
Sarah Connor lived with no global thermonuclear war. The original timeline
still exists, however, in a parallel universe."
T2 implies that its world is of one existence and a single timeline.
Certainly, it would seem to be futile to send someone back to change the
past in a multi-universe existence--unless one is very altruistic! Consider
this: T2 implied that Judgment Day never occurred due to manipulation of the
past. But it all depends which timeline one looks at:
1995 2029 -----|----------------|--(existence with nuclear war) (A) \"_____________"|""(alternate peaceful existence) (B)