Greg Egan - The Clockwork Rocket

“Ah.” Yalda hadn’t had a conversation like this since the long nights she’d spent talking with Tullia—and back then, the roles would have been reversed. “I don’t believe in the kind of predestination that says our actions are irrelevant. So I don’t accept that yesterday would have turned out the same, regardless of what I did.”

“But if your actions aren’t irrelevant, then you can’t be choosing them freely, can you?” Benedetta argued. “If the future is fixed, and your actions affect the future… then your actions themselves must be fixed, otherwise they could lead to the wrong outcome. That means you have no real choice in what you do; you’re just a puppet, steered by forces beyond your control.”

Yalda thought for a while. “Raise your right hand.”

“Why?”

“Go on, humor me.”

Benedetta complied.

“Were you free to raise it or not, as you wished?” Yalda asked her.

“I believe so.”

Yalda said, “Tell me why you should feel any differently about that, depending on whether or not time is a loop and the future is really the distant past.”

Benedetta puzzled over the question. “If it was always going to happen—if in a sense it had already happened —then when I thought I was making the decision, that was just an illusion.”

“An illusion compared to what?” Yalda pressed her. “Tell me how the world could work—how physics could function, how history could be arranged—in a way that would somehow make you ‘more free’?”

“If the future is open,” Benedetta replied. “If our actions are undetermined until we decide what to do.”

“Suppose that really is the case,” Yalda said. “Then what is it that finally determined whether you raised your arm or not?”

“I did. It was my choice.”

“But why did you make that particular choice, and not refuse me?”

Benedetta didn’t reply immediately. “The way you asked, I suppose,” she said finally.

“So I determined your action?”

“No, not completely. My mood, my state of mind played their part as well.”

Yalda said, “None of the things you’ve just referred to disappear from the world if the future is fixed rather than open. Both of us are still here. Our actions are still related in exactly the same way to our wishes, our wishes to our personal moods and histories, and so on.”

Benedetta was not convinced. “If the future is fixed , how can this conversation even mean anything? If it’s an unchangeable fact that I will say whatever I end up saying to you—as if we were just actors following a script—then how can we really be changing each other’s minds? How can we be communicating anything?”

“Do I sound as if I’m making random noises for no particular reason?” Yalda joked.

“No.”

“If there’s a script,” Yalda said, “then we’re the playwrights as well as the actors; there’s no one else who could write our lines. There’s no puppet-master rushing around coordinating everything, forcing us to act against our will—or to make choices that go against our nature—just so history will reach its pre-ordained conclusion.”

“Then how does it work?” Benedetta demanded. “How do things turn out the way they have to?”

Yalda said, “The trick is to stop thinking that it works like fate in the sagas: some tedious monarch overcomes the odds and wins a great battle, because all the bit-players are nothing but cogs whose every action is subservient to his destiny. The reality is the opposite of that: ‘the way things have to be’ is completely unspectacular, and it’s fulfilled at the lowest possible level.

“We don’t know the details for every kind of matter, but in the case of free light the basic building blocks are just cyclic waves. When you make a full circuit of the cosmos in any direction, these waves undergo a whole number of cycles, so they return smoothly to their starting values. That’s it, that’s destiny fulfilled already… because anything constructed from waves like that will automatically share the same property. However complex a pattern of light you build up, it can’t contradict itself when it comes full circle. That’s guaranteed by the lowest-level physics; it doesn’t have to be orchestrated, or scripted, or contrived.”

Benedetta considered this. “So where are we in this picture? If the matter we’re made from works the same way, where are our choices?”

“In our biology,” Yalda said. “I think there’s a degree of consistency between our desires and our actions grounded in the structure of our brains and bodies. What you want, what you do, who you are… these things might not be in perfect harmony, but we’re not prisoners trapped in our bodies while they follow some plan that has nothing to do with us.” At least not until fission took over and split you in four, but Yalda didn’t want to get into that.

Benedetta fell silent as they started across the Great Bridge. Yalda didn’t expect to change her mind on this; the important thing was for her to understand that she could raise anything with her colleagues in the project. When you planned to send a mountain flying through the void at an infinite velocity, there was no such thing as too abstruse a concern.

Finally she said, “I’ll have to think on this more deeply. I can certainly see some force in your arguments.”

Yalda could hear the reservation in her voice. “But?”

Benedetta said, “It’s one thing to argue an abstract case that the future being fixed changes nothing: that there’s really no freedom lost, because our actions are determined in the same way, regardless. The fact remains, though, that we’re accustomed to seeing the future as open. That’s how our lives appear to us, that’s how we usually feel.”

Yalda stopped walking. They were halfway across the bridge, supported by a slender arch of stonework over the blackness of the crevasse. She felt a shudder pass through the skin of her back; she’d just had an eerie sense of knowing what her shy, intense new colleague would say next.

“When our descendants turn around and travel back in time,” Benedetta wondered, “will they still have the luxury we have, of debating this in the abstract? Once past and future are no longer so clear, will they still have the choice to go on seeing things the old way?”

Eusebio counted, “Three. Two. One.”

A distant line of light split the sky, wavering in the heat haze. A pause later the bunker trembled; as the timber boards holding back the sand flexed and rattled, the air filled with fine dust. Yalda and her companions were lying flat on their backs, a stride beneath the ground, but the tilted mirror above let them watch the ascending rocket as if they were upright in the desert, while the tinted clearstone pane protected them from the glare.

Yalda was prepared for the hiss when it came, but not the crack that abruptly bisected the pane along a jagged diagonal. She reached up to support the two pieces before they could slip from the frame and decapitate someone.

Amando cursed quietly and raised his own hands to help; Eusebio did the same, exchanging a glance with Yalda expressing relief that it hadn’t been worse. They’d isolated both the mirror and the pane from ground vibrations, but the shock wave in the air had still been enough to do damage. Nereo didn’t flinch; he was still tracking the rocket with his theodolite, and probably hadn’t even noticed the crack.

Giulio, the journalist from Red Towers, turned to Eusebio chirping with excitement. “To be honest with you, I thought it would just explode on the ground. But it’s really up there!” He was too overwhelmed by the spectacle of the launch to care that he’d narrowly avoided being sliced in two by a giant stone blade.