Jules hits the aisle running at the wrong speed. At the instant he arrives, the Shinkansen with which he was attempting to match velocity is moving at 150 kph, give or take a fraction, but the fraction is significant, and he skids and pratfalls. The lightning flash fades. Re-entry is never pretty, especially in bulky cold-weather gear. It's a known fact that technology improves as time moves on, but to survive being flash-frozen at the skin layer still requires at least a few inches of insulation. He coughs up a lungful of crystallising water vapour. His suit cracks and the thin layer of ice sloughs off in pieces as he stands up, rubbing snow off his nose.
He checks all three of his watches. The timings are good. In his left hand, he's clutching a paper computer. He crumples it up and stuffs it in a pocket. In his right hand, he carries a chunky cylindrical gadget, the latest generation of time machine. Most of it is disposable low-tech battery, now fully expended. He untwists it and throws the two largest pieces in the nearest trash receptacle. Jules keeps a tiny disc-shaped component with a flashing, fluxing Y on one side. That's the reusable section.
"Well, that worked," he remarks to himself. He shrugs the insulated suit off and tucks it under one arm. He straightens his mussed bleached white hair and sincere dark blue tie, and begins to move down the train. Outside, Honshū streaks past, still blurring and accelerating, buildings appearing and disappearing.
As he reaches the door to the next carriage, he looks back and counts a few dozen pairs of Japanese eyes staring at him in astonishment. Nobody's yet figured out if they actually saw what they just saw, but it would be unrealistic to assume otherwise. Jules checks each of his many remaining pockets in turn, eventually finds the memory inducer. He shines it at the passengers' eyes, filling their last few seconds of memories with blank space. That should take care of everything, short of the lightning-burn marks on the seats.
In the vestibule, a ticket inspector asks to see his ticket. The elaborate solution to this problem would have been to buy a used ticket from a businessman just as he got off at Tokyo, and take the ticket back in time, but then there would have been two identical tickets in the system, and one of the two would have been stopped at the gate, possibly introducing a paradox. An even more complex solution would have been to buy the ticket by post from a prior century. A surprising number of businesses in the world, spanning a surprising number of centuries, are, have been, or will be willing to accept a fee and sit on an envelope for fifty years or more before delivering it. Some of these establishments, mostly banks and legal firms, are known to be unreliable, experiencing natural disasters or financial trouble in a majority of timelines, and retroactively receive no business. Others have a proven record, make their way onto the widely-distributed List, and become so overwhelmed that they set up special departments to handle the work. The record for a successful delivery is (for a given value of "is") just over four hundred years.
But it was easiest to just visit the station on the day when the security cameras were down.
Jules bows and smiles and exchanges pleasantries with the inspector before moving down the corridor. His Japanese is excellent.
Picking his father's wild white hair out of the lineup in the next carriage is the work of a moment, even just squinting through the perspex in the door and going by backs of heads. Jules composes himself before walking into the next carriage. When he walks in, with his smart conventional suit and tie, he looks like any professional Western businessman, circa 1980 to 2050, other than the tell-tale whiffs of CO2 still sublimating from the coat under his arm. He strides through, stows the coat overhead, sits down in the spare seat and doesn't even glance at his father's ageless face. "You know, this train isn't even touching the ground?"
"Incredible, isn't it? I remember a time when magnetic levitation was the stuff of science fiction! Of course, I remember a time when horseless vehicles powered by petroleum were the stuff of science fiction. And sanitation. And good teeth. That was only last year, from my perspective. Who are you?"
"If my history's correct, you're sixty-seven and towards the end of your exploration of the 1984-prime-2 outspirals. Which means we've met at least of couple of times already, objective past, so don't give me that. Dad."
"Yes, yes. Jules. It's great to see you. Your mother sends her regards, as ever. But I need to know which you you are."
This is far too complicated to explain. Jules hands over his paper PC. "Check my time sheet."
His father gasps. He flips the paper over a few times, creasing and uncreasing it. Bright, moving, interactive images, on a sheet as thin as a dollar bill. "Unbelievable! What year is this from?"
"Oh, come on, Dad."
"You can tell me. I promise not to invest."
"You'd better not. This is an early-generation model. This model was too robust, if you can believe that. They cost a fortune to grow, and never got popular. The company went bust after making just a couple thousand. The later models tear so easily, they're practically disposable."
"They actually grow these things?"
"Oh God, Dad, don't tell me you don't know about organic computing. You've visited me in the future enough times."
"Not yet, subjectively! Alright, alright. I can't help myself. It's the same when I read fiction. I just can't put a good book down. I'm just ravenous to find out what happens next. Speaking of which. What's the weather like in 2045?"
"This is a hell of a time sheet, son."
Jules takes it back and stuffs it guiltily in his pocket again. "I know. What can I say? What did you always say? You can never simplify your life through time travel, only other people's."
"Indeed so. Now, if I were a betting man, which I most assuredly am not, I'd bet that you've met future mes a fair number of times. Which is interesting, because it means you deliberately came back to meet me when I was younger. Why is that, I wonder?"
They stare out of the window at the rushing scenery for a long familial moment, while the train covers two miles. On the horizon, a skyscraper wavers in the air, shifts to the left slightly, and then vanishes. Jules' eyes widen and he hopes his father hasn't noticed. But he has.
"Did you see that? The ripple effect."
Jules' face falls into a rictus of guilt. "Yeah."
"And there! Did you see? That suburb all but vanished while we were travelling! If much more of this happens the train itself could drop out of existence!"
"We're fine on the train," Jules explains. "The train is inviolate. I've learned that much from experience. While we're above eighty-eight miles per hour, we should be safe. On an airplane would have been ideal, but I needed you to see the scenery."
"Someone must be changing history. But who? And why? And where, and when?"
"Would I be here if I knew?"
"Jules... What have you done?"
"I don't know! I don't think I've done it yet! I should have destroyed your work, Dad. You shouldn't have even told us who you really were, or where you were really from. If two guys in a garage can build a time machine, what could... I don't know, one of the big Japanese or Nigerian corporations do? They could figure out how to exploit causal loops to get research done faster. They could import plutonium from the future. My home town started changing size, and changing Mayor. I visited the town square, and the statue of Franklin was back there in one piece. My house disappeared, then some other family was living there. Then it came back. I hit the historical logs and tried to catch up with a major change as it was happening, but by the time I got close to any firm point of inflection, something else had happened before it and the ripple effect had already moved that whole timeline out of joint and erased it. It was like chasing a ghost."
"Of course..." The older man, "Doc" to his friends but always "Dad" to his sons, has a distant look in his eyes. A slight gleam. "Whether or not my work is destroyed is irrelevant! You can't blame yourself for not destroying my work, or me. You can't destroy science. You see, time travel is built into the fabric of the spacetime continuum. There was always a chance that someone would independently rediscover the same thing I discovered."
"But what about all that stuff about the galaxies unravelling? None of that has happened!"
"Of course it hasn't happened! Why would anybody intentionally destroy the entire Milky Way? If a corporation of some sort were at the root of the problem then it would be very obvious which one, because after each ripple the corporation would have become more and more powerful and profitable. What have you seen in your logs? What did you see on your street corner every day? New corporate logos? Advertisements and franchises?" Jules shakes his head. "What about political groups? Religious groups? Did you ever find yourself not living in the United States? Was the country ever at war?"
"Nothing like that happened, Dad," says Jules, shuffling through data in his computer looking for evidence of the patterns his father is suggesting. "It was all just... variations on a theme. Different buildings here, different shops there, different faces, different jobs and news stories. One day I didn't have any kids, the next day they were back. I've had a rough couple of weeks, subjective."
"Then it must be an individual. I believe that you're dealing with somebody highly intelligent and purposeful, with a strong understanding of the laws of time travel and a very specific goal in mind. They must be taking a methodical approach to engineering a perfect stable universe."
"...Not a Tannen," Jules remarks.
His father says, "No Tannen across all of spacetime was ever smart enough to manipulate time like that."
"And it's not me. You know I was never the scientist you were. I just push buttons on the interface like a common monkey. If you're right... within known spacetime, that narrows the field to just two people. You, and Harry Dyne."
Jules blinks. "Harold Thaddeus Dyne. You know who Harry Dyne was. Your mentor."
Jules' father stares blankly back at him.
"...He helped you build the first time machine. And... you said that there is no stable universe with time travel. You and Harry proved that mathematically. Continuous change is the inescapable nature of reality. You taught me that when I was six years old!"
"I built the first time machine by myself. I thought I misheard you earlier. Did you say nineteen eighty-four?"
"It's personal," realises Jules. He stands up and looks in each direction along the train. Outside, the curve of the track wavers among multiple possibilities, collapsing just in time as the train passes over it. Hills which would have been cut away to make room for the track disappear and reappear in different configurations—
"It's personal. There is no stable universe with time travellers. Only chaos."
Jules grabs his snow gear from the overhead compartment and hurriedly puts it on and zips it up. He pulls two more power cells out of side pockets and begins screwing his time machine back together. "I knew it. I've been followed. We'll be decelerating into Tokyo in a few minutes. We have to get you... Dad... Oh, shit!"
The seat's empty. Not even warm.
Jules zips up his hood, but he doesn't have time to start jogging to match pace with his re-entry vehicle before the train drops back below 142 kph. There's a lightning flash, and all that's left is a pair of flaming rubber footprints.