This is the fifth post in a ten-part series about my ongoing workshop “Creating Consistent SF-Worlds” for the Game Design department at the Mediadesign Hochschule in Düsseldorf, Germany.
Part I | Part II | Part III | Part IV | Part VI
Time Travel and Time Machines
After focusing on the design of consistent star systems and star drives, we started the fifth session with our third major topic, time travel and time machines. As with star drives, “objective” consistency—as opposed to “subjective” or “narrative” consistency—had to be checked. In this case, it yielded a rather asymmetric picture. Interestingly enough, the most formidable obstacle to practical time travel into the future turns out to be the lack of suitable starflight technology, while traveling into the past seems all but impossible except on levels that are screamingly abstract.
Before we jumped into our topic of the day, though, we embarked on a digression on “free will” and why we’d get along perfectly fine without this powerful illusion while still retaining our moral compass and our ability to act ethically. Certainly, we didn’t neglect to outline the sociological and psychological challenges attached to liberate oneself from these age-old clutches of the “free will” illusion, namely our strong urge for retributive justice, punishment, and even personal vengeance—as opposed to concepts that, especially for those who were victimized, are often deeply unsatisfying, namely concepts of justice that focus on protection & safety, rehabilitation, and reintegration. All this, as we will see, has implications for time travel; implications that became visible later when we proceeded to discussing the possibility or impossibility of changing the past.
But first, we started with differentiating distinct modes of time travel: classical time machines (H. G. Wells, DeLoreans etc.), starflight technology (warp drives, wormholes, slingshots etc.), and different kinds of traveling with the mind (meditation, paranormal activity, drugs). Then, we discussed the various means of time travel into the future, followed by certain possible and impossible means of time travel into the past. Finally, we considered the question of paradoxes any change of the past might engender.
To sum up the most important aspects: most of the consistent modes of time travel, i. e., science fiction time travel, not fantasy time travel, are strongly connected with certain modes of starflight technology which we covered two weeks ago. (Some concepts of which we expanded upon later that day after our session, thereby touching on black holes, event horizons, and Hawking radiation, over great bowls of
liquid nitrogen ice cream and iced coffee). Given advanced star drives, time travel into the future is actually a piece of cake. To start with, there is no rule that restricts wormholes, for example, to transport a traveler through time as well as through space. (Remember, time and space are not really that distinct when we approach the very big and the very small.) The easiest road into the future, though, would be time dilation, whereby gravitational time dilation is particularly useful: given a kick-ass starflight engine that can keep up constant acceleration, a traveler could in principle make a round-trip through the observable universe in her (subjective) lifetime, but she wouldn’t exactly be back for dinner. (Think of several billion years that will have passed on Earth.) Also, we briefly touched upon the problem that superluminal speeds, depending on an observer’s frame of reference, allow information to travel forward in time, with disturbing consequences for FTL settings.
Now, how about traveling back in time? Thanks to wormholes (see above) and general relativity, this should be possible in principle. Kurt Gödel found a solution to Einstein’s field equations which describes a universe very similar to ours, except that it rotates and is composed of a perfect fluid under constant pressure. (Okay maybe not that similar, but close enough to worry.) In this universe, travelers in rocket ships (yes, you need proper starflight technology again) can move, within their regular timeline, along loop-shaped “world lines” and arrive in their own past, and they can do so easily and at any point in this universe. Actually, travelers could navigate to any point in their past or future as easily as we can move to any point in space in our universe. So there is at least one universe, perfectly consistent with natural laws, where time travel is a natural phenomenon. And according to Gödel, there’s nothing that would prevent these travelers from changing their own past as they see fit.
Which led us to our final problem: time travel paradoxes, the most famous of which is certainly the Grandfather Paradox. Among physicists, there is a certain tendency to support two seemingly incompatible premises: 1) the possibility of time travel into the past cannot be ruled out completely; 2) changing the past is impossible. Of course, there are scenarios that would satisfy both premises. Three of which we came up with were:
1. The Oedipus Tyrannos Principle
Any change I make in the past would inevitably turn out to have taken part in establishing what happened in the first place. It’s like what all the characters do in Oedipus Tyrannos: the harder they work toward changing the inevitable, the harder they work toward making the inevitable happen.
2. Split Timelines
If we leave the Copenhagen Interpretation and postulate a “real” wavefunction for the universe toward the many-worlds interpretation, we can weasel our way out of any paradox if we assume that every change in the past opens up a new timeline that “branches” away from the one we came from.
3. Dominant vs. Fading Timelines
Again connected to the many-worlds interpretation but focusing on probabilities, the “split timeline” scenario can be tweaked to the effect that the changed past becomes “more probable” over time while that branch of the past we came from, and which we remember, becomes less and less probable and finally fades away.
But none of these solutions actually allow for an actual change of the past. Which is fine for consistency but where does that leave us in the light of our initial digression?
All seems well when we ourselves are the ones who travel into the past. But what if a time traveler from the future comes back to her subjective past, which is our present? What would it mean if this traveler “couldn’t possibly change anything” with respect to her past which is our very future? Now, even if our actions are not “free” in the sense the free-will illusion suggests, we are still free to act. In Free Will(y) I wrote:
Which doesn’t mean that this “me” isn’t real, of course it is real, but it’s not real the way we think it’s real.
Or, as Sam Harris puts it in The Moral Landscape:
To see this is to realize that you are not the author of your thoughts and actions in the way that people generally suppose. This insight does not make social and political freedom any less important, however. The freedom to do what one intends, and not to do otherwise, is no less valuable than it ever was.
So how can we have intentions and, more importantly, act on these intentions within a context of social and political freedom, when a time traveler from the future wouldn’t be able to change anything that, for us, hasn’t happened yet? Would we be “more free” than the time traveler? That, of course, would hardly be a practical solution; if we were free to act, we could inflict changes that would prevent the time traveler from visiting us in the first place, and we’d be thrown back to square one: the Grandfather Paradox.
I could imagine some possibilities to weasel our way out of this through philosophy, but I’d rather weasel my way out of this through physics. Have your say!
Anyways. One thing I liked about Terminator and Terminator 2: Judgment Day were the clever screenplays (Cameron, as suggested by Avatar, must have forgotten all about that). They mostly rely on the Oedipus Tyrannos scenario but break out of it eventually with Sarah Connor’s voice-over when they approach the Cyberdyne compound, a voice-over I found essentially soothing:
The future, always so clear to me, has become like a black highway at night. We were in uncharted territory now… making up history as we went along.
Neurons in the cerebral cortex
The Time Machine
Screenshot Terminator 2: Judgment Day