One of the great things about science fiction is how it allows an author to explore the human condition in contexts that ordinary fiction cannot. For example, it can explore the idea of immortality. Is boredom a problem? If you are immortal, but others aren’t, what is it like to see everyone you know age and die? Is it as desirable as it seems?
Some themes occur repeatedly in science fiction. Immortality is just one. A very common one is the idea of alien races — or even intelligent machines. Such stories view humanity through new eyes.
Another common one is time travel, and that is the subject of today’s Sci-Fi Saturday!
The problem with time travel is that (unlike aliens or immortality) it’s almost certainly impossible. The idea of going into our own past seems inherently contradictory. On the other hand, we all are traveling into the future at the rate of one year per year.
Of course, that’s not what people usually mean by time travel. Just that we’re all doing it together at the same pace without any special machinery or magic makes it mundane and ordinary.
It turns out that, because of Special Relativity, if you board a fast spaceship, travel away from your start point really fast, and then come back (again really fast, or it would take forever), you “time travel” into the future of the people you left behind.
For example, if your spaceship flies at merely half the speed of light (something we can today foresee accomplishing), and you take a trip to a star six light years away, immediately turn around and come back, upon your return you will have aged 20.8 years.
But everyone on Earth will have aged 24! You have effectively traveled almost four years into the future. At higher speeds, this effect becomes pronounced — you can effectively travel many hundreds of years into the future.
The catch is: you can’t come back. It’s a bit like being in suspended animation for those years (assuming you age more slowly) and then being woken up (this, too, is a science fiction theme that traces back to Sleeping Beauty and Rip Van Winkle).
Why is time travel into the past problematic?
A common scenario involves traveling back into the past and killing your father before he marries your mother. (Or less violently, just preventing that marriage.) That action prevents you from being born — it prevents you from existing!
So who came back to prevent the marriage? This is another form of the Liar’s Paradox. (“This statement is false.”) Various authors (and some scientists!) have devised answers to this problem. I’ll explore some below.
The logic paradox I like even better is this: Suppose future Wyrd Smythe comes back and gives me the plans to a time machine. I spend years building the machine so that I can come back and give myself the plans.
Where did the plans come from?
It’s almost a version of the Fermi Paradox: If time travel was possible, where are the time travelers?
I have time travel on the brain because I’ve just finished re-reading a bunch of Poul Anderson’s Time Patrol stories.
Anderson’s approach is a fairly common one: the past can be changed, and this does change the future. Time travel was given to us by a version of humanity far into the future (and far evolved above us). They establish the Time Patrol to protect the timeline — in fact, to protect themselves.
But the timeline has a kind of inertia — actually affecting the future requires the right effort at the right time. Anderson often uses the analogy of a mesh of rubber bands. Stretch one part of the mesh, and it snaps back.
Here, if you do manage to affect the future, your future may vanish. The circumstances that created you may cease to exist. But because you’re in the past, you still exist — you don’t suddenly vanish. You can even travel back to the future to a world that no longer contains your parents.
In that new future, if you do and see things, then go fix the past to restore the original timeline, that new future vanishes, but you still remember what you did and saw. Your personal timeline is consistent.
A plot tension point is that, if Time Patrol people in the past innocently return to the future — a future that’s been altered by the past — they, too, can vanish along with that new future if other agents fix the past and restore the timeline.
Some scientists have floated the idea that time travel into the past might be possible, but doing so puts you into a different timeline. If you prevent “your” parents from marrying, you prevent the “you” in that timeline. This is somewhat similar to the Many-Worlds Interpretation of quantum physics. This idea does away with all the paradoxes of time travel.
Another way authors have dealt with the problem is to invoke a form of “cosmic censorship.” The Superman stories used this idea. Superman sometimes traveled into the past (because he’s super) and tried to change events to create a better, or at least different, future.
But something always happens to prevent those attempts. (Ultimately he stops trying.) The universe finds some way of thwarting his effort.
A variation on this is that a time traveler ends up causing the very event they tried to prevent. Upon returning to their present and taking a closer look, they find they were always there and always caused that event.
Time travel also has the interesting idea that we can know we did a certain thing in the past before we go back and do it. (Many authors mention the difficulty of tenses when talking about time travel! The Time Patrol has its own language designed to deal with that.) This invokes the idea of having to actually go back and do it. Or not!
There is also the idea of what is sometimes called the “block universe” — that the past, present, and future, all exist. Time travel just allows you to move around in the block. If you change the past, it turns out you always did.
One of the more intriguing short SF stories I’ve read involves a race that perceives time as a dimension. They know the future as well as the past. An analogy is made to the telling of a known story. The beauty lies in the telling, not the knowing. (There is, perhaps, a hint of Stoicism there.) The other analogy is of how little children can watch a favorite movie over and over. They can know every word of dialog and still revel in the re-telling.
I really enjoyed the film Looper, which has time travel at its center. One of these days I plan a whole post about it, so I won’t describe it here — see the linked Wiki page if you want details now.
One element I found interesting is how, if an older version of you is in the past, and someone damages (or kills) your younger self, the change works its way up your timeline and ultimately affects you.
It is not the case that you were always damaged and always knew you were; you suddenly become aware that you are now damaged. This is not a new idea — that changes in the past propagate forwards at some pace is just one more take on time travel that authors have used.
If I recall correctly, Gordon Dickerson’s Time-Storm uses that idea. Or maybe I’m thinking of another novel. I do believe the series finale of Star Trek: The Next Generation also used it.
A film widely acknowledged as almost a tutorial on time travel is the rather inaccessible (and hard to find) Primer. I’ve seen this film twice and been utterly lost both times. Even the diagrams I’ve found that try to explain the film are complex and confusing!
Time travel, unlike immortality, or aliens, or even warp drive (which is also probably impossible), is rife with paradox and built-in contradiction. And that just makes it a fun mine field to explore!
I’ll leave you with a quote from Poul Anderson’s The Shield of Time. It comes from a Danellian — one of our highly evolved distant future selves — to comfort two agents who’ve twice restored the prime timeline from disastrous, future destroying, changes. But that also means they’ve vanished two entire timelines filled with billions, some of whom they’ve come to like.
“Some evolutions are, on balance, better than others. This is simply a fact, like the fact that some stars shine brighter than others. You have seen a Western civilization in which the Church engulfed the state, and one in which the state engulfed the Church.
What you have rescued is that fruitful tension between Church and state out of which, despite every pettiness, blunder, corruption, farce, and tragedy — out of which grew the first real knowledge of the universe and the first strong ideal of liberty.
For what you did, be neither arrogant nor guilt-laden; be glad.”
Stay timely, my friends!