13 August 2022

"Hey guys, I don't---*guys!* Over here, quick!"

Mason reluctantly pried his eyes away from his computer screen. Ada undid a wrist strap and stood up from the soldering desk. They both made their way over to J.D.'s workstation. He was fairly vibrating with excitement.

"You know how we've been trying to find a way to preserve fidelity in the uplink chipset?"

Mason yawned and rubbed his eyes. They'd been in the lab since yesterday afternoon, and the pale dawn light beginning to intrude through the blinds was an unwelcome sight. "You mean we were trying. Dude, we've been over this. There's no way to clean up the signal degradation. It's a dead end."

J.D.'s normally sober expression was replaced by a goofy grin. "You mean it was a dead end. We've got another chunk of the transmission, and this one had a complete algorithm for boosting signal cohesion by a lot. We're talking like three or four orders of magnitude, easy."

This got Mason's attention, and he stared dumbly at J.D. They'd spent weeks trying to coax a little more efficiency out of the chipset, and now J.D. was talking about an unconscionable thousand-fold improvement. If it were true, it would make all of their hard problems easy, and their easy problems trivial.

He shook his head. "Three or four... you're shitting me, right? You've gotta be shitting me." J.D. cackled with delight and pointed to the screen. Mason leaned closer and saw a comment block by J.D.'s finger, a small island of text nestled among reams of code:

    //      -future mason

Mason couldn't help laughing too. The first time they'd read one of these prescient messages from Future Them, they'd been shocked and humbled, and sat for a long time in a silence pregnant with metaphysical implication. But by this point they'd stumbled onto a half dozen more, and it had become good clean fun. Besides, seeing as mucking around with time would probably end up transforming every aspect of human existence sooner or later, Mason found it comforting to know he'd still be taking pleasure in the little things a few months down the road.

Meanwhile, Ada was completely absorbed. Her dark, serious eyes were scanning through the program, a perplexed look building on her delicate features. "J.D., hold up. Have you actually tried running this yet? Because this is completely impossible. We tried everything. It'd have to be some radically different approach, and---well, nothing here looks new. All I see is a bunch of Mason's garbage code."

"Aww, you're just jealous that I'm the one who figures it out," Mason said cheerfully, giving her a playful punch in the arm. "Garbage code my ass. Twenty bucks says this thing runs flawlessly out of the box."

J.D. shrugged. "I know one way to find out."

They'd picked up the transmission some months back, but soon discovered that because of some unexplained glitch---they weren't even sure whether it was on the sending or receiving side---large swaths of data had been corrupted. Fortunately, a few sections here and there seemed to be intact; it was enough, just barely, to determine from whom and when it had been sent.

As for the corrupt data, they'd found most of it padded with enough redundancy to be theoretically recoverable; in practice, this required a large and unpredictable number of CPU cycles. As a result, the summer had consisted of long stretches spent beating their heads against some intractable problem, punctuated by intense flurries of activity whenever a chunk finished processing.

But the waiting was worth it. Every time the Oracle---J.D.'s tongue-in-cheek name for the recovery software he'd written---spat out something new, they learned something ranging from fascinating to invaluable.

Whenever they ran into a particularly stubborn problem and were ready to chalk it up as a loss, the Oracle would offer up some key insight or bit of code that would propel them further along. Future Them seemed to have no compunction about reaching back with a helping hand to guide them forward.

There were exceptions. Part of what they recovered turned out to be plaintext messages from themselves. Sometimes they were jokes ("time humor" as J.D. took to calling it), and occasionally they bordered on the inane ("you'll never guess who Mason's sister hooks up with.")

That last one had put Mason in a foul mood. He'd stormed around the lab and complained bitterly: "What's the deal?? Where the fuck are all the lotto numbers and stock tips?"

J.D. patiently reminded him that they wouldn't be able to send anything back that would change how things played out this time through. Mason grabbed a worn tennis ball from the floor and flopped back in his chair. He started bouncing it off a nearby wall and continued to grumble. "Hell with that. When it's my turn, I'm sending back all the cheats I can."

J.D. sighed. Mason was a top-shelf coder, but he didn't have the same instinct for the knotty science of it that he and Ada had developed. "I'm sure you will," he replied. "Hey, you know what? That's probably what sets off the glitch that nukes half our data."

"Wait, what? What's that mean?" Just then, a door slammed shut behind them, and they both turned around to see Ada walking in, balancing a tall cup of something Starbucks on a stack of binders. "Hey, Ade, impeccable timing. I think J.D.'s accusing me of sabotage. Or intent to sabotage." She cocked an eyebrow at him from across the lab.

"Come on, you're supposed to know this stuff by now," implored J.D. "One of the most fundamental tenets of modern physics is that causality is always preserved. If someone seems like they're about to violate it---say, by sending back lottery numbers that we know you never actually receive---then something is going to stop him.

"That much we know for sure. The speculative part is what exactly the 'something' would be, but our best guess is that in the absence of any other selection effect, it tends to be some confluence of high-entropy events. Like your flash drive cuts out at the exact right instant to make sure your lotto numbers are wiped---and who knows what else gets fried as collateral damage.

"It's good not to think of your intended action as 'causing' something to step in and stop it, though. Whatever happens was going to happen all along, precisely because events couldn't have played out any other way." He paused, looking for any sign of recognition on Mason's face. "You seriously don't remember how this works? Dr. Abel and I spent all last fall fleshing it out, and you were cc'd on everything."

Mason stopped bouncing the ball as Ada pulled up a chair. "Yeah, now that you mention it, that rings a bell. Problem is, haven't we already violated causality? The Oracle has been dropping hints since day one. We never would have figured out half this shit on our own."

Ada jumped in: "Never? There's a huge difference between 'not ever' and 'not quickly.' All the problems we've had help with so far strike me as the sorts of things we'd be able to crack on our own, sooner or later..." She trailed off, looking confused. "But J.D., I've got to admit that I don't see why sending back code is okay, but lotto numbers isn't."

Mason was clearly delighted. He did a fist pump and shouted, "HA! See? I knew Ade had my back."

J.D. shrugged indifferently, and said, "Look, if nothing else, we know that's how it works because that's what happened---will happen. We have code. We don't have stock tips. I'll admit I was surprised myself when the answers started coming in, but the bottom line is that they did, so it must not be breaking the rules."

This still seemed like a contradiction, but Mason knew he wouldn't get anywhere by arguing it, so he decided to stick with being an ass. "If you're right, and I was the problem, isn't it kind of a good thing? I mean if it was 'cause of me trying to send sensitive shit backwards, I just won't do it this time. Then we get our complete transmission."

J.D. started to laugh. Ada turned to him in mock exasperation. "He is kidding, right? He realizes that if it is his fault, there's nothing he could 'do differently this time,' right?"

"I get what you kids are saying, but hang on, hear me out," insisted Mason. "The past is the past and there's nothing anyone can do about it, even with time travel. I get that, I really do. But now you're trying to tell me the future is the past, too? If what's done is done, and what will happen must happen, seems to me like past and future are kind of munging together. I mean, what the hell happened to self-determinism?"

"It is so too early for this conversation," muttered Ada, standing up and grabbing her coffee. J.D. appeared lost in thought; Mason looked on expectantly. After about a minute, he spoke.

"Well, it's complicated," he began...

>> Chapter 3