The Rules of Time Travel 3/4

We do not go back in time to kill our grandfathers.

Do Not Create Paradoxes

“All right,” said Font, ambling along the rows of students. “Who can tell me what the various types of paradoxes are?”

A forest of hands shot up.


“You go back in time,” he said, scribbling on the passive screen. “Then you find your grandfather. And you accidentally kill him.” More scribbling. “What happens downstream?”

“You die,” drawled a student from the back row.

“Wrong!” said Font cheerfully, throwing the stylus pen onto his podium. “It can’t be done. Killing your grandfather, I mean.”

It was truly remarkable how much these kids thought they knew.

“Look,” he said, cutting through the whispers, “some of you may know about the Proximity Effect.” He paused and watched the smarter and/or better-read ones eye him. “That effect worsens the further you go up your genetic lineage.”

Font picked up the stylus again and twirled it expertly around his fingers. “The Proximity Effect is what happens when you travel within your own timeline and you approach, physically approach, your past self. Now, this is an introductory course, so I won’t go into the principles of entanglement, but suffice it to say that it becomes far too painful for a Traveler to actually be near his past self.”

“Now,” and he started drawing family trees on the screen, randomly joining circles across from different families until he had about fifteen ‘children’. “You kill your parents, and what you’re doing is wiping out yourself. Kill your grandparents, you wipe out your parents and your aunts and your uncles… and so on.”

The stylus stopped. “Now, the great and wonderful Fabric of Space and Time knows that it’s a huge paradox. It knows that you shouldn’t be contacting yourself or hurting yourself in the past. It knows, therefore, that you must not kill your grandfather.”

Font thumped the stylus against the screen. “And it tells you by increasing the Proximity Effect. Once you go within a fifty mile radius of your grandparents in the future, you need to be hospitalised.” He paused. The class looked suitably impressed. “What, you thought we did genetic screenings because we liked ‘em? No, we need to establish who’s related to whom, if any of the past-people we’re about to visit were related to you.”

He tossed the stylus up and caught it without looking. “Next!”


“The origin’s a little thorny,” said Font, wandering up the rows of students. “It is classified as a paradox, but isn’t actually classified as catastrophe-level.”

He pointed to a thoughtful looking girl. “Why’s that, miss?”

“Um,” she stuttered, “because – well, origin basically means the object is taken out of history, right? And if that object is, er, in isolation from the rest of history… then it doesn’t affect history very much, does it?”

“Yes,” said Font, and leaped down the rows to seize the stylus again. “Now, here’s the future tech,” he said, drawing a line and a point at the end of it. “You bring future tech into the past.” An arrow, and another dot. “Then past starts developing technology from the future tech. By the time you’ve gotten to the ‘original future’” – here he pointed to the first dot – “the tech you brought into the past is gone, it’s obsolete.”

He stepped back from the diagram and squinted at it. “So – where did it originate from?”

The class was kind enough to give him suggestions, but they all thought so linearly still, Font mused. “No, not the future, not the first dot – because it’s not there anymore! That technology is done at that point. It’s gone.”

He waved dismissively at someone else. “Nope, not the past either, it originated from the future, remember?”

The tumult died down after a while and Font spread his arms. “It doesn’t have an origin! We didn’t call it the origin paradox because it was a pretty name – we honestly can’t tell in those cases what happens to them.”

“And really, it’s not a big deal.” Font smirked a bit. “It’s only one object that’s unanchored in time, and the chances of it affecting anything else are miniscule2. They are capable of being positive influences, when we speed up the development of certain technology3.”

There was much desperate copying and recording, and Font let it go on for a few more seconds before he thumped the stylus down on the podium again.



“Now,” said Font, brandishing the stylus. “Let’s have a demonstration of the loop paradox.”

And the screen filled with light.

“No eye cameras existed at the time of this incident,” said Font, standing against the holograph. “This was the very first few years of Travel, where boundaries between historian and coldjumper weren’t precisely defined, and when we didn’t have nearly as many checks and balances.”

The holograph showed a static picture of a man and a woman, both shy but beamingly happy, dressed in clothing from about two generations earlier.

“Let us,” said Font, “call the man Frank and the woman Clare. When they met, Frank told Clare he was on assignment from out of country, which explained his slightly different accent and his rather strange clothing.”

“But Clare noticed also that Frank seemed to perform some actions – such as booting up her desktop computer – not as though he was familiar with them, but as though he had learned them somewhere and was replicating the actions.”

Font flicked to the next slide, a truly awful standard-issue Chron In identification card. The same man, but perhaps slightly younger, a half-smile on his face. It was an ancient card, though – no one carried around facial identification anymore, not when everything was genetic.

“Frank, you notice, was actually a Traveler. This card was issued about fifty years ago, at the dawn of the Traveling age. One of Frank’s assignments was a series of visits to about sixty years earlier than his time… on some kind of mission I am apparently still not at liberty to discuss with you.”

Font arrested an eye-roll. “On one of these scheduled visits, he met Clare. They got along like a house on fire. He kept returning, and on what he knew was his last visit, he gave her an Infused pendant.”

Some of the girls in the class were looking distinctly dreamy.

“Infused pendants, as you know, glow in a rather lovely way when they touch the skin. But that technology was developed only about a year before Frank left for his series of assignments. So, first of all, he has behaved anachronistically. Of course, no one had any idea. But Frank was the reason Chron In introduced organic camera eyes.”

Font flipped to the next picture, which was of two houses side by side – the first, looking brand-new, dated around the time of Clare, and the other, older and nobler looking, dated around Frank’s time.

“Clare kept that pendant. She showed it to only one person – her granddaughter – but never wore it in public. When she died her house -” Font’s stylus hovered over the new-looking house on the left “ – became a museum of antiquities. Her granddaughter didn’t know what happened to the pendant.”

Font brought up the next holo, a video this time. The pendant in question reposed in dark silk, its opal-like surface glowing against the background. A hand reached into the silk, scooped out the pendant, and held it in hands covered by thin surgical gloves. In a few seconds, the opal was shining brightly, a small friendly flame against the hand.

“One of our authenticators came over to value the materials after they went on public display. She verified that the pendant wasn’t ‘antique’ but was quite definitely contemporary. It was, in fact, an Infused pendant.”

Font leaned against the podium and allowed himself a small, grim smile. “The pendant was taken off display but was put somewhere in reserve after that, in a place only historians would really want to venture. As I’ve mentioned, job titles were fluid then – Frank was a historian as well as a Traveler.”

The next video had certainly been taken by a small security camera. The class watched, still puzzled, as the camera showed Frank pausing by the pendant, inspecting it for a good five minutes, as though confused about how it came to be in a section for antiques, and then absentmindedly pocket it as he walked out.

“Frank certainly didn’t know about the controversy regarding the pendant, because he’d been away training recently. He thought it was simply a cheap but nice Infused pendant. He picked it up, walked out, and of course, proceeded to give it to Clare at the end of his assignment.”

Font paused. Some of the students were sitting back in their chairs with slightly dazed looks, comprehension slowly dawning.

“Many paradoxes are variations on circular logic – we don’t know where the beginnings are.” Font drew in a breath and whooshed it out. “Loop paradoxes are particularly insidious because we actually don’t know how they happen.”

Font had to speak over the rising babble of astonishment. “It’s – just imagine a natural disaster – except in time, all right? Somehow a loop is created. You can argue however much you’d like that it’s pre-destiny or whatever – loop paradoxes are possible, but we’re still learning why.”

He pointed randomly. “Now, you – tell me, why didn’t Chron In do anything about it?”

“They… couldn’t?” said the girl, hesitantly. “Because… if they interrupted him before he gave her that pendant, then… how would he even have it?”

“Precisely,” said Font crisply. “And that is where our problem lies.”

“Any paradox creates problems within space-time.”

Font grabbed a loose thread in his tunic. He always seemed to have one of those hanging around. “Imagine it’s like one of those retro cotton outfits where you take a thread that’s sticking out and you start pulling… but it begins to unravel the whole outfit. The paradox is that thread, and for us to tamper with anything to do with it will begin to unravel our own space-time continuum.”

“The only thing to do is to secure the time zones before and after the area of the incident – essentially making the fifty years before and after completely unavailable for further Traveling. And fifty years…” Font paused and stared around at the class. “Fifty years is a long, long time for the Chronological Institute.”


“I am reluctant,” said Font, “to discuss the omission paradox with you. As you know, it’s an ill-defined area, both when it comes to identifying it, and rectifying it.”

He paused. Several of the students looked mutinous, but most of the class simply looked resigned. The omission paradox was like… a black hole, perhaps, Font thought. It did have a proper definition, but that description was so difficult to get across to people that it was sometimes easier not to try. And very few attempts had even been made.

A majority of the recruits simply knew the official ChronIn definition: “That a lack of person, thing, or circumstance would prevent some significant event in history from happening.” A few of them were smart enough to figure it out, to be sure, but a majority had accepted the definition because it was, after all, official.

And there was, of course, a reason why it was so vaguely defined. Font had to walk a thin line between respecting that reason, and actually teaching these youngsters.

Thankfully, he’d have help this year.

Font sighed. “All right, let’s try it this way. Say that a coldjumping team traveled back around 500 BCE, and that he met Siddhartha Gautama. Perhaps he realized that Gautama never left his palace, never saw the sights of the aged and deceased – unless someone specifically led him to do so. The Traveler then realizes that he is probably the most convenient person for the job.”

For nearly a minute, the class was silent, digesting the most concrete example of the omission paradox they’d ever heard. Then Font heard the whispering start as they began to think about the implications.

A voice cut through it, clear and sharp with suspicion. “That’s… writing yourself into history, isn’t it? Whoever did it would be part of history – what else could a Traveler ask for?”

“Precisely,” Font agreed mildly. The girl who’d spoken leaned forward across her crossed legs, looking eager.

“So there have been cases, then? How purely theoretical is this?”

The quicker students were already flicking through newsfeeds on their tablets, trying to see if they could spot anything from the ChronIn spokespersons.

Font smiled tightly. “Three documented cases. None of them public.”

“So the omission paradox isn’t purely an academic exercise, then,” the girl stated flatly.

“Why, no,” said Font pleasantly. “And what are you planning to do with the knowledge, miss?”

The girl looked slightly incredulous. “You don’t honestly think that, given a chance to do something really important, some of us won’t take it. Not all of us are interested in just being time-detectives.”

There was an odd tightening of the tension around the room. Someone had come out and said it – but now it was out in the open. Font could almost hear them wondering about the details of the three cases.

“What I am interested in,” said Font thoughtfully, “is how you intend to take that chance. When do you know you’re going to encounter an omission, exactly?”

The girl shrugged. “We’ll just have to be extra good then, won’t we? Keep our eyes peeled, keep doing research.”

“And what will you do when you can’t find an omission?” said Font, quietly. “Will you create one?”

The class fell silent.

“It’s a slippery slope, isn’t it?” Font continued inexorably. “Perhaps one day you’re idly speculating on the chances of an omission; the next week you’re searching actively, the month after that you manage to get onto a team that’s going to a time period you’re interested in. What then?”

“Will you, perhaps, kill Gautama’s assistants so that you can have the pleasure of assisting him yourself? Or would you kill Gautama himself and be the Buddha?”

The girl looked slightly sick.

“If we want to consider the entire spectrum of the omission paradox,” Font continued, “then we need to consider both the positive – that is, the preservation of history – and the negative – the sabotage of history.”

He leaned back against the podium and let his gaze sweep around the room. “We can only be prepared for an omission paradox. We cannot know history, or its characters, so intimately that we know exactly when to step in. But when it happens, we need to be ready.”

Font smiled humorlessly. “Which brings me to the next rule of time travel – the unofficial rule for anyone who wants to be a Traveler: do your research.”

“It’s not simply to find a neat little omission paradox,” said Font, stalking around the classroom. “It’s so you can get personally acclimatized to the century. Of course, the only reason we have Travelers now and not coldjumpers is because our geochronohistorians have become so good at keeping track of history that we can arrive at our historical locations without too much trouble.”

“But quite recently, one of our GCHs made a tiny mistake.” Font stopped at the back of the classroom, watching the students crane their heads towards him as he walked down the stairs. “He sent a highly qualified Traveler into the past – the American 1800s – with almost entirely adequate preparation.” Font paused at the foot of the stairs and swiveled to face his students. “Except, of course, that the Traveler was dark-skinned.”

Most of the students looked confused, although some were catching on, to judge from their apprehensive looks. “In America in the 1800s, slavery still existed. And most of those who were dark-skinned were African-Americans, who were the slaves themselves. The Traveler was nearly sold off to a household as part of a human auction.”

The class looked horrified, and deeply disgusted.

“It was an almost acceptable mistake to make, considering that none of these prejudices are present in our current century. Until fairly recently, not many departments kept track of the cultural and ethnic backgrounds of their travelers, or passed them on to the GCH.”

Font had reached the podium now, and he rested his arms across it. “So who is ultimately responsible for their own welfare?”

The class murmured variations of “the Traveler is”.

“So,” Font continued, “it behooves you to do some of your own research, to put yourselves in the shoes of the time-location that you will be traveling to. Realize that GCHs may not even be attached to the department you are in, that our records may not contain enough personal information to let the GCH know how much danger you may or may not be in.”

Font gave them all a sardonic smile. “So this lady here has brought up an important point, despite the circumstances which the point arose from – if you intend to be Travelers, whether you want to be an omission hero or, you know, someone who survives and gets back to our time – doing your own research is crucial. I cannot stress this enough.”

The bell rang, with uncannily perfect timing. Font thought of it as his reward for carrying this lecture off fairly well.

“I expect you all to have finished the optional readings as well, by next week. You may leave. Why don’t you walk with me, miss?” he added, giving the troublemaker a quick grin. She stood, somewhat haughtily, and marched to his side.



1.The Big Red Alarm of Doom, or Brad, as it was affectionately called, was Font’s idea. Brad beeped when the historical inaccuracies (noted by those huge servers, which stood in a time-static room) ratcheted up past a predetermined level. But those inaccuracies didn’t usually spring from one cause – they were the results of a miasma of jumps that each resulted in a minute change. Individually, those changes meant nothing, but history made a strange synergy out of them that meant that the early death of a cloth merchant in the 1600s resulted in no plastics being produced in the 20th century. The job of a first-cause detective was to root out the cause of those catastrophes that plagued Brad and its faithful assistants.

2. Font is not being entirely truthful. Any paradox hurts time, stitches it up in a way that makes those few years before and after the event dangerous to traverse. Origin paradoxes are not nearly as dangerous, certainly, but the five years before and after the event need to be cordoned off whenever they occur – meaning, no Traveler can visit those times anymore.

3. When the first developers of true AI created their final product, they tampered a bit, going back in time to influence future tech so that they could speed up the process. It’s a bit like cheating, but hey – they were on a budget that was even more shoestring than Chron In’s! And it wasn’t as though the Board of Global Controllers specified five years in linear time or five years with added time jumps



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