What Is Time Travel?

Lately, I’ve been on a time-travel kick, enough so that I decided to make a list of time travel stories that I’ve read or watched. Of course, that brings up the question of exactly what is time travel? After all, I have to have some criteria for including or excluding a story in my list!

With that quetion in mind, I read the excellent comprehensive treatise on the fiction and the theory of time travel: Paul J. Nahin’s Time Machines: Time Travel in Physics, Metaphysics, and Science Fiction (second edition). I give it five stars for sure! I don’t think that Nahin gives a concise definition of what he considers to be time travel, although he does give some negative examples and he rejects a quote from H. Bruce Franklin that “when one says time travel, what one really means is an extraordinary dislocation of someone’s consciousness in time.”

So, here’s my attempt at a definition:

Time travel is any backwards or discontinuous occurrence of the usual situation of cause preceding effect.
That’s my definition, and I’ sticking to it. In order to be considered time travel, moving to the future must be discontinuous: I am here and now, then without occupying the intervening time, I am at some future time. Anything going backwards is time travel. So, some examples that are gnerally not time travel:
  1. Viewing the past
  2. Viewing a possible future as in A Christmas Carol, even if that future comes true as in Life-Line
  3. Sending information into the future
  4. Predicting the future, even should your predictions come true without fail
  5. Time dilation via fast travel or gravity
  6. Moving from our world to that of Conan the Barbarian
  7. Dreaming of the past or future
  8. Bringing Benjamin Franklin’s ghost to life
  9. Bizarre physiologically aging, forwards or backwards, while experiencing time in a normal fashion
  10. Experiencing time passage at a faster rate or slower rate than normal
  11. Stopping time
  12. If at any point there is a whole bodice, and at some subsequent (or previous) point there is a bodice that is less than whole, then the story is not time travel.
On the first four items, I'll make exceptions on a whim.

For the most part, if the characters of the story believe that the events in the story actually happened in their own world, then I shall trust the story is not a dream or travel to a separate world&mdashso, yay for Connecticut Yankee in King Arthur’s Court! Oh, and any comic books after 1969 that purport to have time travel are wrong. This is because after that date, everything in comic books was time travel, which is logically equivalent to nothing being time travel.

Please enjoy! —Michael Main (main@colorado.edu)