“I wanted to ask you something. Did you get a chance to read that document yet, that I sent you?”
Philip’s notes. “Yeah, a couple of days ago. It was…it was hard stuff to deal with, and I’m still thinking about it. Alicia, seriously, it’s way too early, can we just—”
“Oh, excellent, that’ll make this much easier. I’d really like to buy you breakfast, Rebecca. This morning. Say, in one hour.”
But they had just gone running together last week, and had planned to go running together again tomorrow! This was a strange conversation, but Rebecca, who was beginning to feel more awake now, reasoned that Alicia probably knew it was strange because Alicia was the one who was making it strange.
“Why don’t we meet at that place where we go sometimes after our little jaunts?” Alicia said.
Marian’s Diner. That greasy spoon on Route 1. “Sure.”
Alicia sounded like she was afraid of someone eavesdropping. Why would she be worried about surveillance?
“A friend of mine you know will be there, too,” Alicia said. “A bunch of old friends, having a reunion. A grand old time.” Nothing anyone would want to observe. The “friend” had to be Carson: who else?
“Okay,” Rebecca said, hoping to God she wasn’t about to get drawn into some stupid love triangle thing. “See you in a bit.”
When Rebecca entered Marian’s Diner a little over an hour later, in faded jeans and an old T-shirt, her hair pinned up in a sloppy topknot, Alicia and Carson were waiting for her, sitting next to each other in a booth whose other side was empty. Carson still looked half asleep—he was wearing a button-down shirt whose pattern of wrinkles indicated that he’d pulled it from the bottom of a laundry hamper. Alicia, on the other hand, looked perky and fresh-faced, in a navy-blue baby-doll T-shirt that read STRATTON UNIVERSITY DEPARTMENT OF PHYSICS. The two of them had an easy familiarity about them, though when Carson looked up and saw Rebecca approaching, he slid a few inches away from Alicia, probably unaware that he was doing so.
At this time of morning the diner was nearly empty, save for a couple of truckers at the counter and a portly character whose three-piece suit with its shiny elbows fit him like a sausage casing. He was speaking loudly into one of those old mobile phones, the kind that flipped open and had a keypad. “I don’t think you know who I am,” he said. “I don’t think you realize that you are wasting the time of a very important man. My time is the greatest gift I can give.”
A waitress sauntered over with a coffeepot and three mugs soon after Rebecca seated herself, taking the desire for caffeine as a given. Rebecca got steak and eggs; Carson opted for French toast with a side of hash browns; Alicia ordered the cricket cinnamon pancakes. “No syrup, please,” she said. Rebecca involuntarily frowned.
“Gotcha,” the waitress said over her shoulder as she left the table. Alicia then reached into her pocket and pulled out some kind of electronic device that was about the size and shape of a USB stick. “I picked this up in London while I was there for a conference last year. Makes moviegoing heaven.” She flicked a slider on the side of the stick with her thumb, and a blue light began to flash at its tip. The Very Important Gentleman at the nearby table took his phone from his ear, squinted at its tiny screen with a frown, and flipped it shut.
“Now,” Alicia said, “we can begin. Rebecca. A question. When you entered the causality violation device. Did you—”
“Oh, come on. I’ve already apologized for that, I’ve already explained, you’ve already deactivated my keycard. How many times are you going to go back to that—”
“This isn’t about that. Well, it is. But not in that way. Think back. Remember when you went inside. Did you observe anything interesting?”
“It was…dark? Pitch black, like you’d expect it to be: it doesn’t have any windows, and the lab was pretty dim anyway. I didn’t see anything out of the ordinary. And I was only in there for a few seconds, anyway. Maybe thirty seconds. I mean, the machine doesn’t work, right?”
Alicia and Carson said nothing and merely looked at each other and back to Rebecca, as if one of them wanted the other to speak. Rebecca sat back in her booth, looking at the two of them incredulously. “The machine doesn’t work,” she said again. “Right?”
“Keep your voice down,” said Alicia, looking over at the Very Important Gentleman, who in turn was staring at the three of them.
“I’d better explain,” said Carson.
“Explain what?” Rebecca hissed.
Carson smiled weakly. “How time travel works,” he said, and though Rebecca got the impression that this was intended to be funny, she also had the feeling that not much of this was funny at all.
“Okay,” Carson said. “Let’s look at this this way. There’s what I guess you’d call a traditional time travel story, that everybody hears as a kid in one form or another. Ray Bradbury wrote one of these, originally. I forget how it goes exactly, but it’s like: It’s the future. And there’s a big game hunter who’s killed one of everything that’s interesting, so he goes back in time to whatever-it-is BC to kill a dinosaur. But while he’s back there he steps on—a butterfly, isn’t it?—and—”
“And when he gets back to the future it’s turned into some god-awful police state,” Rebecca finished. “I had to read that story in school.”
“And it’s never really explained how that happened,” Carson continued, “but the implication is that without that butterfly doing whatever it did, there would never have been a Declaration of Independence, or the Allies wouldn’t have won World War II, or some other thing like that. But the explanation isn’t important. You don’t need that for the story to work. What’s important is that when the time traveler comes back to that terrible future, he remembers the original future he came from, compares it to the one in which he now exists, sees that this new future is much worse than the old one, and realizes that it’s his own fault. That a bit of carelessness in the past, one that would have been trivial if it were not for time travel, has had some catastrophic consequences.
“But look at it this way. Imagine a time traveler who lives in a fantastic future—replication technology has eliminated scarcity; chocolate candy falls from the sky at four o’clock each afternoon. He goes back in time and he steps on the butterfly. That changes history so that this good future never happened. The time traveler returns not to the good future, but the bad one. Smoke-filled skies blot out the sun; the brains of the poor are being harvested to feed to the rich. But if the good future never happened, how would the time traveler be able to remember it? Because it didn’t happen, right?
“If the future changed, and the time traveler we’re talking about was from that future, and was the product of events that created that future, why wouldn’t the time traveler also change when those events changed?”
“There’s one way around it,” Alicia said, taking over from Carson as their orders came out. “You could consider the idea of the multiverse, and think of it as something like a tree—that is, the universe we live in is one of an uncountable number of branches of possible universes, created by random chance and the decisions of sentient beings. So, for instance, when I rang you up this morning, there was a possible future universe in which you answered the phone, and another in which you did not, and by answering the phone you put us in one universe and not the other. In that instance the time traveler doesn’t just move from the future to the past and back to the future: he moves down one branch of the universe, toward the root that’s back at the beginning of time, and back up another branch.
“And you can see a couple of reasons why that’s appealing. First, the idea of the multiverse is essentially the fantasy of preserving perfect information. One of the hard things to deal with in life is the fact that you destroy potential information whenever you make a decision. You could even say that’s essentially what regret is: a profound problem of incomplete information. If you select one thing on a diner’s menu, you can’t know what it would have been
like to taste other things on it, right then, right there. When you marry one person, you give up the possibility of knowing what it would have been like to have married any number of others. But if the multiverse exists, you can at least imagine there’s another version of you who’s eating that other thing you thought about ordering, or who’s married to that other man you only went on two dates with. Even if you’ll never see all the information for yourself, at least you’ll be able to tell yourself that it’s there.
“The second reason the multiverse seems like such a neat idea is that it gives human beings just an incredible amount of agency, which they can exercise with the least effort. Why, Carson here created an entire alternate universe when he ordered hash browns on the side with his French toast instead of bacon—”
“Ah, I should have gotten bacon, how could I forget,” Carson said, and attempted to hail the waitress.
“But the history of science shows that any theory that covertly panders to the human ego like that, that puts humans at the center of things, is very likely to be found out as wrong, given enough time. So, just for the sake of argument, let’s assume that there’s just this one universe, and we’re stuck with it. What happens to our time traveler then?”
“Alicia let me see some of Philip’s notes,” Carson said after the waitress dropped off a fractured coffee saucer with two strips of fatty bacon hanging off its edge. “Not all of them—I understand there’s some personal stuff in Philip’s comment code that’s not my business. But there are some undeveloped ideas in there that we’ve been kicking around. And we have a theory that fits the facts, and Philip’s comments as well.”
“I don’t like it,” Alicia said, “and I think that any sensible person would be well within their rights to dismiss it as crazy, and for reasons that will soon become self-evident, I would really rather it isn’t true. But it fits the facts, and we have to consider it.”
“What we are proposing,” Alicia said, “is that the laws of physics are such that causality violation is subject to a form of version control, one that prevents a forking of history. That instead of causality violation creating an alternate universe, one version of history is outright overwritten by another. One past is replaced with another past. Which means one future is replaced with another future. Which means that the memories of the past of the people in that future are replaced with memories of a different past.”
Carson interrupted. “Including the memories of any—”
“Purely hypothetical—”
“—time travelers.
“So take our time traveler from the traditional story,” Carson continued. “He leaves his utopian future for the past. He kills the butterfly. The Magna Carta is never written. He returns to the dystopian future that his misstep created. But he doesn’t see it as a dystopia: he sees it as home, the world he grew up in, the world he left to go back in time. Because he doesn’t remember that first future, and has no other world to which he can compare this one. Maybe he even sees it as a utopia. Maybe everyone does. Maybe everyone in this dark place believes that they live in the best of all possible worlds.”
Rebecca said nothing, but ripples appeared on the surface of the coffee in her cup as her hand began to tremble.
“Here’s what we already think or know is true about causality violation,” Alicia said. “We know that if it’s possible, the circumstances under which it can occur are highly restricted. We can’t send an object into the future because we don’t have the necessary information—we can’t predict with sufficient accuracy where the earth will be in space at a given time. And the law of conservation of mass and energy dictates that an object that undergoes a causality violation must return to the exact point in spacetime from which it departs when the violation begins.”
“For instance,” Carson continued, “we have this robot, Arachne, that we’ve been sending into the causality violation chamber for experiments. The idea is that we send it back into the past. But it can’t stay there, because the raw materials that constitute Arachne already exist in the past in another form: maybe they haven’t been excavated from a quarry yet, or maybe they’re in some kid’s gaming console, but they’re there. The rule is simple: in a closed system, mass cannot be created or destroyed, and the universe is the largest closed system there is. So you can’t duplicate a mass by sending it back in time: the law of conservation would be violated. Causality violation is only feasible because it exploits a loophole in the law: it cheats it temporarily, but not permanently.”
“For certain contingent values of ‘temporarily’ and ‘permanently,’ ” Alicia clarified. “By the way, our explanation is going to get a little weird now.”
“But the point is that if Arachne returns to the exact point in spacetime that she left, then there’s still a contiguous history in which mass is constant, so physics lets us off the hook.”
“This would be true not just for an object, but for a person,” Alicia said. “And when we talk about that, that’s when things will get really weird.”
“I’m not sure I’m going to enjoy your idea of what ‘really weird’ is,” said Rebecca.
“So look at the experiment we’re doing,” Carson said. “We have this robot. It has a clock attached to it that syncs to the atomic clock in Boulder, Colorado, before it enters the causality violation chamber. If it works as we believe it should, and it never has, it should go back to Point Zero, the place in spacetime from which we measure the relative movement of the chamber through space as it moves forward in time. It should remain there for one hour, then reenter the chamber and return to the present. From the point of view of the observer, all this should occur instantaneously. So when the robot emerges from the chamber, its clock should be one hour behind the clock in Colorado.
“You can think of the robot’s clock as analogous to the memory of the time traveler in the traditional version of the time travel story. He carries his old memories with him into the new world, compares the two, and has his evidence that he has traveled through time. Similarly, a one-hour discrepancy between Arachne’s clock and the clock in Boulder would be evidence of a successful causality violation.
“But it may be—and we think this is what Philip may have been working his way toward—that this isn’t how it would work. The consequence of the causality violation might not be as neatly localized and observable as we expect. It’s possible, say, that if we send Arachne into the chamber at four o’clock, and it remains in the past for an hour and then returns to the present, it might return to an altered version of the present in which the robot was sent into the chamber not at four o’clock, but at five o’clock. The robot would not record the discrepancy in its clock; we would not notice it, because this new version of history would have no record of the old one. From our perspective the experiment would appear to have failed. There would be no evidence.”
“I don’t like where this is going,” said Rebecca. “Because I went into that chamber. And, to be honest, I was kind of drunk when I did.”
“I’ve been in there, too,” Alicia said. “Several times.”
“Me, too,” said Carson. “And Philip entered it a number of times as well.”
“Representatives from that creepy quasi-military organization that funds us—DAPAS—they’ve been in there. They were footing the bill for the research, so even though they wouldn’t know a causality violation device from a Star Trek transporter and had no business going near the thing, I wasn’t going to keep them out.”
“How many times do you think someone’s gone inside that machine?” Rebecca said. “That you’re now speculating wouldn’t look to you like it would work, even if it did.”
“When our measurements said it was operating, even though there was no observable effect?” Carson said. “A few dozen? More?”
“That guy from DAPAS brought his kid along, remember that?” Alicia said. “ ‘Hey, Oscar, come here. Wanna play in the time machine?’ I think he was six.”
“Wait a secon
d,” Rebecca said.
“I have to repeat that this is all highly, highly speculative,” Alicia said. “I’m not going to have a clean explanation for all of this. We’ve only been working on this idea for a few days.”
“Well, I’ve got some questions anyway. Like, a bunch.”
“That’s reasonable.”
“First of all. You’re saying that the robot is analogous to the time traveler in the story. In the story, this time traveler makes this horrible future because of something he does in the past. What does the robot do in the past? To make a new future? Surely she’s not going to step on a butterfly, or reset her clock, or something.”
Alicia and Carson sat there for a moment, and then Carson said, “Maybe the action that creates the new future isn’t the one that takes place in the past. Maybe the act of creating the causality violation in the first place by sending the robot back in time is what creates the new future, and the rest of what happens in the past is—”
“Don’t you say it!” Alicia interrupted.
“—predestined,” Carson finished.
“I told you not to say that! I really do not want to go there.”
“But we’ve got a ton of free will problems to deal with anyway,” Carson said. “Why not pile more on top?”
“So we might as well head in that direction now,” Rebecca said. “Because there are some serious issues of free will here. My dad’s a minister: his head would explode, thinking about this.”
“I told you this would get weird,” Alicia said.
“First of all—okay. This conservation of mass thing. If the robot goes back in time it has to return to the same place it left. Fine. Did you try sending it back and telling it to stay back there?”
“Sure we did. Before we figured out the problem, we tried a few runs where we programmed it to go back to Point Zero, move a couple of hundred feet away from the chamber, and shut down, thinking that time’s natural course would carry it forward to us in the lab, where we could download its data and see our results. We thought we could send Arachne into the chamber and she’d appear outside it, like a magic trick. But it never worked. The robot just wouldn’t leave.”