She had been lovely twenty years hence; surely, though, she was even lovelier now. Surely—

Yes, yes, there was still anticipation, still wonder, still tension.

Of course, she'd seen him naked, too, twenty years further down the road. He knew what she looked like — her chestnut hair color was natural, or at least dyed in both places; wine-colored nipples; those same enchanting freckles painting constellations across her chest. But him? What did he look like twenty years hence? He was no athlete even now. What if he'd put on weight? What if his chest hair had gone gray?

Maybe her present reluctance was based on what she'd seen of the future him. He couldn't promise he'd work out, couldn't promise he'd keep trim, couldn't promise anything — she knew what he'd be like in 2030, even if he himself did not.

"It's good to see you again," said Jake, trying to sound calm, trying to sound warm.

"You, too," said Carly. And then she smiled.

"What?"

"Nothing."

"No, come on. Tell me."

She smiled again, then lowered her eyes. "I was just picturing us naked," she said.

He felt his features stretching into a grin. "Me, too."

"This is strange," she said. And then: "Look, I never go to bed with anyone on the first date. I mean — "

Jake lifted his hands off the tabletop. "Me neither," he said.

She smiled at that. Maybe she was as beautiful as he remembered after all.

The Mosaic Project didn't just reveal the futures of individual human beings. It also had a lot to say about the future of governments, companies, and organizations — including CERN itself.

It seemed that in 2022, a team at CERN — Theo and Lloyd were on it — would developed a whole new kind of physics tool: the Tachyon-Tardyon Collider. Tachyons were particles that traveled faster than the speed of light; the more energy they carried, the closer to light-speed they traveled. As their energy went down, their speed went up — to almost infinite velocities.

Tardyons, on the other hand, were ordinary matter: they traveled at speeds below that of light. The more energy you pumped into a tardyon, the faster it would go. But, as old Einstein had said, the faster it goes, the more massive a tardyon gets. Particle accelerators, such as CERN's Large Hadron Collider, worked by imparting great energies to tardyons, thereby boosting them to high speeds, and hurtling them togethe r, releasing all that energy when the particles collide. Such machines were huge.

But imagine taking a stationary tardyon — a proton, say, held in place by a magnetic field — and getting a tachyon to collide with it. You wouldn't need huge accelerator rings to get the tachyon up to speed — it was naturally whipping along at superluminal velocities. All you needed to do was make sure that it hit the tardyon.

And so the TT Collider was born.

It did not require a tunnel twenty-seven kilometers in circumference, as the LHC did.

It did not cost billions of dollars to build.

It did not demand thousands of people to maintain and operate it.

A TTC was about the size of a large microwave oven. The early models — the ones available in 2030 — cost about forty million American dollars, and there were only nine in the world. But it was predicted that they'd eventually be cheap enough that every university would have its own.

The effect on CERN was devastating; more than twenty-eight hundred people were laid off. The impact on the towns of St. Genis and Thoiry was also great — suddenly over a thousand homes and apartments became available as people moved away. The LHC would apparently be left operational, but would rarely be used; it was so much easier to do, and redo, experiments using a TTC.

"You know this is crazy," said Carly Tompkins, after taking a sip of her Ethiopian coffee.

Jake Horowitz looked at her, eyebrows raised.

"What happened in that vision," said Carly, lowering her eyes, "that was passionate. It wasn't two people who had been together for twenty years."

Jake lifted his shoulders. "I never want it to get stale, to get old. People can have a good love life for decades on end."

"Not like that. Not ripping each other's clothes off in the workplace."

Jake frowned. "You never know."

Carly was quiet for a moment, then: "You want to come back to my place? You know, just for coffee… "

They were sitting in a coffee shop, of course, so the offer made little sense. Jake's heart was pounding. "Sure," he said. "That would be nice."

Another night at Lloyd's apartment, Lloyd and Michiko sitting on the couch, no words passing between them.

Lloyd pursed his lips, thinking. Why couldn't he just go ahead and commit to this woman? He did love her. Why couldn't he just ignore what he'd seen? Millions of people were doing just that, after all — for most of the world, the idea of a fixed future was ridiculous. They'd seen it a hundred times in TV shows and movies: Jimmy Stewart realizes that it's a wonderful life after watching the world unfold without him. Superman, incensed at the death of Lois Lane, flies around the Earth so quickly that it spins backwards, letting him return to a time before her demise, saving her. Caesar, son of the chimpanzee scientists Zira and Cornelius, sets the world on a path of interspecies brotherhood, hoping to avoid Earth's destruction by nuclear holocaust.

Even scientists spoke in terms of contingent evolution. Stephen Jay Gould, taking a metaphor from the Jimmy Stewart movie, told the world that if you could rewind the skein of time, it would doubtless play out differently, with something other than human beings emerging at the end.

But Gould wasn't a physicist; what he proposed as a thought experiment was impossible. The best you could do was a riff on what had happened during the Flashforward — move the marker for "now" to another instant. Time was fixed; in the can, each frame exposed. The future wasn't a work in progress; it was a done deal, and no matter how many times Stephen Jay Gould watches It's A Wonderful Life, Clarence will always get his wings…

Lloyd stroked Michiko's hair, wondering what was written above this slice in the spacetime block.

Jake was lying on his back, one arm bent behind his head. Carly was snuggling against him, playing with his chest hair. They were both naked.

"You know," said Carly, "we've got a chance for something really wonderful here."

Jake lifted his eyebrows. "Oh?"

"How many couples have this, in this day and age? A guarantee that they'll be togethe r twenty years from now! And not just together, but still passionately in… " She trailed off; it was one thing to discuss the future, it was quite another, apparently, to give premature voice to the L-word.

They were quiet for a time. "There isn't somebody else, is there?" asked Carly, finally, her voice small. "Back in Geneva?"

Jake shook his head, his red hair rustling against the pillow. "No." And then he swallowed, working up his courage. "But there's someone else here, isn't there? Your boyfriend — Bob."

Carly exhaled. "I'm sorry," she said. "I know a lie is a terrible way to begin a relationship. I — look, I didn't know anything about you. And male physicists are such hound dogs, really they are. I've even got an old wedding band I sometimes wear to conferences. There is no Bob; I just said there was so I'd have a convenient out, you know, if things didn't seem to be going well."

Jake didn't know whether to be offended or not. Once, when he'd been sixteen or seventeen, he was chatting to his cousin Howie's girlfriend on a July night, out front of Howie's house. There were a bunch of people around; they'd been having a barbecue around back. It was dark, and it was clear, and she had struck up a conversation with him, after noting that he was looking up at the stars. She didn't know any of their names, and was stunned that he could point out Polaris, plus the three corners of the Summer Triangle, Vega, Deneb, and Altair. He started to show her Cassiopeia, but it was hard to see, half obscured by the trees rising up behind the house. And yet he wanted her to see it — the great W in the sky, one of the easiest constellations to spot once you've been introduced to it. And so he said, here, cross the street with me, you'll be able to see it from the other side. It was a nice suburban street, devoid of traffic at that time of night, with lit-up houses behind neatly trimmed lawns.