Changing the Past

I've recently finished the latest book by S. M. Stirling (best known for alternate history SF), a time-travel adventure, TO TURN THE TIDE, first volume in a new series. Partially inspired by L. Sprague DeCamp’s vintage novel LEST DARKNESS FALL (but Stirling's book is better), TO TURN THE TIDE transports a Harvard professor of history and four graduate students to central Europe in 165 A.D., era of the Roman Empire under Marcus Aurelius. They know they've made a one-way trip, since the time machine is stationary instead of a vehicle like the one in H. G. Wells's classic, so they decide to use the literal ton of supplies sent with them as planned by the inventor of the machine (who accidentally fails to come along as he'd meant to). They set out to change history for the better, beginning with simple improvements, e.g, sterile medical procedures and wheelebarrows, and building on their early successes. In this first installment of the series, their innovations consist of “Type A” changes, things the inhabitants of that era and locale can implement with available tools and materials once they’re given the concepts. “Type B” developments, those that require inventing the tools to make the tools to construct the new things, will come later.

In fiction, altering the past in an attempt to improve the future produces a wide range of effects. At one extreme, we have Ray Bradbury's story of a tiny, accidental change with disastrous results, when a visitor to the age of dinosaurs crushes a butterfly, thereby generating a future worse than the one he originally came from (yet unrealistically similar, but, then, it's a short story with no real pretense of scientific rigor). At the other extreme, some of Heinlein's fiction, notably THE DOOR INTO SUMMER, postulates that any alteration you make in the past isn't a real change at all. You're just doing whatever you did in the first place but weren't aware of in hindsight until after you went back and did it. (Is your head spinning yet?) Likewise, in one of the Harry Potter books, the actions of Harry and Hermione when using the time turner simply cause things to happen just as they had all along, previously unknown to the characters. In Diana Gabaldon's "Outlander" series, Claire (the traveler from the 20th century to the mid-18th) and Jamie strive to prevent the 1745 Jacobite rising and Bonnie Prince Charlie's invasion of Scotland. Although not completely powerless, they find their major goals unattainable. After the war unfolds on schedule, culminating in the catastrophic battle of Culloden despite their strenuous efforts to influence the course of events, they realize they can make only minor changes. It's as if the flow of time resists any significant alterations.

Time travel seems to work similarly in Connie Willis's series about mid-21st-century historians from Oxford. The transporting device can't send them anywhere close to a major historical event. If they deliberately or inadvertently aim for a critical nexus point, the traveler is simply bounced to a different nearby location. Thus the timeline corrects itself, smoothing out any ripples the characters create. Or so they believe -- this postulate is tested in the two-volume World War II epic BLACKOUT / ALL CLEAR, in which the historians fear they may have triggered disastrous changes in the original history.

The major theoretical issue with trying to improve the future -- one's own present -- by altering the past is what happens if you succeed. You would have had no reason to go into the past in the first place, and therefore you couldn't have peformed the actions that result / resulted / will or would result in achieving your goal. Many time-travel authors simply ignore this paradox. Some stories work on the premise that the travelers exist in a sort of bubble, in which only they remember both the original timeline and the new one, while everybody else is oblivious that anything has changed. The most logical solution is the outcome Stirling implies: The paradox makes it impossible to reshape one's own original history. Instead, the chrononaut's actions generate a new timeline branching off from the point of intervention. The protagonist of TO TURN THE TIDE can never find out whether that's what happens in the history he and his friends are creating, but the question is moot anyway. In the future they left, every person and thing they knew and loved has almost certainly been wiped out in a nuclear holocaust. Their hope is to spawn a new future without that apocalyptic destruction, even though they'll never know whether they've succeeded.

Although the "branching timelines" model makes the most rigorous sense, I do enjoy stories in which the protagonist achieves positive change by tweaking the past and returns home to enjoy the fruits of his or her efforts.

Margaret L. Carter

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