“It’s benign,” Amanda said. “The growth.”

Jonas felt a cataract of relief. He exhaled and gripped her hand tighter. The room seemed to brighten, despite the blinds. “Oh thank God,” he breathed. “That’s great. That’s—that’s the best news ever.” He felt giddy. Lightheaded.

But then, just as quickly, he paled. He assumed Amanda was tired, her sallow appearance the result of postoperative fatigue or anesthesia or both. But he was struck with the realization that her pallid look was due to neither of these things. He felt his stomach bottom out. Something was still tragically wrong.

Amanda swallowed hard. She started to cry. “Because of the surgery,” she began, speaking with a slow tentativeness, “Dr. Gilberg . . . she says . . .”

Jonas held his breath. He felt little pieces of himself die in each of her silent pauses.

“She says that it’s very unlikely . . .” Amanda clamped her mouth shut against the sobs trying to escape from it.

Jonas put another hand over hers. “Whatever it is, it’s okay,” he assured her, meaning every word. “It’ll be okay. You’re okay. That’s all that matters.” He had never believed anything more.

But Amanda shook her head in defiance, rejecting Jonas’s assertion that she was okay. “She doesn’t think I’ll be able to get pregnant.”

Jonas was instantly hyperaware of his surroundings. The monitoring devices Amanda was wired up to, which had previously seemed as quiet as a whisper, seemed to thrum loudly. The blinds hung over the window like garish teeth. Beyond them, a siren warbled past. Outside, behind the window’s divide, life spun on, ignorant of the hopes and dreams evaporating within the hospital room, unaware that futures barely imagined were being erased.

“We never talked about having kids,” Amanda said. “But I always assumed . . .”

“Me too.”

Jonas didn’t know what else to say. In the hours and days that followed, though, he wished that he had. He weighed how he could be so heartbroken over a possibility he had never really thought about before, let alone discussed with the woman he was to share his life with. How had they never talked about whether the contours of that life included children? Had they both been too focused on their work? Or did this omission, shocking in hindsight, speak to a larger issue?

Jonas was seized by a horrible and profound fear. Was this the beginning of their end? He tried to push the thought away. But it was too late.

NOW

In the aftermath of his conversation with Eva, sleep eludes Jonas. He wakes in the middle of the night and tries to work, but he cannot focus. All he can think of is her—the first “her” that isn’t Amanda in as long as he can remember. She’s there, sleeping in the next room, this other woman whom, in the solitude, in the quiet hours of the evening, he can admit that he loves. He can even confess to himself that he might feel the potential of a love to rival what he feels for Amanda.

Eva’s twenty, thirty steps away. She might even be waiting for him, as unable to sleep as he is. She could be sitting up in her bed or staring up at the ceiling, waiting in her bedroom for him to enter, offering everything he needs in his soul. Love and companionship and sex, yes. But also closure. She’s tempting him with peace, the end of his long, difficult struggle.

When he closes his eyes, he sees Amanda. Go to her, she tells him. Move on from me. Move on with your life.

He wants to cry, but the tears won’t come. He wants to scream, but Eva would hear. He is so very tired, but sleep refuses him, and so fatigue just pulls at him like a weight.

Thinking that fresh air is what he needs, he escapes out into the night. His joints moan in protest as he walks. Other Jonas had told him this is a sign of his body losing its ability to reality-slip. Is it possible that he’s lost it already? That he’s waited too long and is now confined to this universe? If so, he’s rejected Eva in the name of a woman he will never be with. He’s marooned in the desert and just refused an oasis.

He walks for hours. Stars glister overhead. Eventually, the horizon glows, and the rising sun renders the sky a brilliant orange. As the world brightens, Jonas wanders the paths of Hijiyama Park. The cherry blossoms are in bloom, tiny explosions of color dangling from branches. He finds a bench and watches the park fill with joggers and dog walkers. As they pass, Jonas thinks of each of their unique lives multiplied by an infinite number of universes. He imagines an endless tapestry woven from threads of such variety that they form a sea of color, rainbows on rainbows.

He pulls a five-hundred-yen coin from his pocket. Flips it. Catches it. Flips it again. Flip. Catch. Flip. Catch. After a minute, it takes on the quality of silent meditation. Flip. Catch. Flip. Catch. Flip. The morning sunlight glints off the coin’s golden circumference as it tumbles in the air. Its motion reminds him of the limousine careening off the Centralbron, gravity causing it to pinwheel like the coin. Flip. Flip. Flip. With the exception of only two realities, the limousine’s fatal roll—in a multiverse of uncountable universes—ends with Amanda’s body broken on impact. Tails, you lose.

Jonas loses himself in the repetition. The light playing across the coin. The faint harmonic ting it makes when launched by his thumb. The percussive thwack as he snatches it from the air. Flip. Catch. Flip. Catch. Flip. The runners and trotting dogs on leashes give way to morning commuters who give way to tourists and bird-watchers. And still he sits. Flip. Catch. Flip. Catch. Flip.

“What are you doing?”

Jonas catches the coin and looks up. It’s Eva. Her eyes are red from crying. He doesn’t think to ask how she found him, and she doesn’t offer. He flips the coin again.

“Birthing universes,” he says. A new one with each flip. Schrödinger’s yen.

“I thought you said it didn’t work that way.”

“I don’t know anything anymore,” Jonas answers. His voice is distant. Unmoored. A moment of silence passes. Another to add to the pile of such moments that by now rises as tall as a mountain. Finally, he rises to his feet. “I’m sorry,” he says, and means it.

“This would be easier,” Eva replies, “if you didn’t apologize.” Her voice remains even, her jaw tight.

“What would be easier?”

“Are you finished?”

Jonas doesn’t understand. “Finished with what?”

“Your calculations. Whatever you need to do with your tether. Are you ready to go?”

“Yes.” In truth, he finished only the previous night, while sleep eluded him like a fugitive.

“I called Dr. Kobayashi this morning,” she says. “He’s expecting us.”

Suddenly, the world seems clearer, brighter. The birdsong wafting through the park takes on a cheery timbre. Jonas looks at Eva, this incredible woman. This woman who can think of him even after he’s broken her heart. This woman who chooses him even though he rejected her.

“What did you tell him?” he asks.

“I told him a colleague of mine needs a favor, but the request has to be in person.”

“Probably safer than the truth.”

“Probably.”

Her heartbreak seems all the more gut wrenching for the will she’s summoning to overcome it. “Eva . . . ,” he says, unsure of what words will follow.

“Loving you means helping you,” she says, answering the question held in his thoughts but not formed. “I don’t like it, but that’s how it is. Because if you don’t find her . . . then it was all for nothing.”

Jonas marvels at the enormity of the gift she’s given him, greater than anything he can conceive of. He’s panged by the guilt of knowing that loving him as she does means letting him go to be with another woman in another universe. The idea is so big that he couldn’t embrace it even if his arms were the diameter of the world.

Eva looks away. It seems as though she might cry, but no tears come. Instead, a curious smile forms on her lips. Her voice carries the slightest lilt of hopefulness when she says, “Somewhere . . . there’s another me. And there’s another you. And that you . . .”—her voice pitches upward—“that you chooses to stay.”

She turns toward him, her eyes still lit with the spark that envisions a reality where the two of them are together and that may have been one of the hundreds of universes Jonas might have just created by flipping a coin.

It takes a little over an hour for Jonas to return to the apartment, calibrate his tether with its new battery, and change into his all-natural “traveling clothes.” The living room turned workshop is a muddle of whiteboards, stray dry-erase markers, and tangles of wire. It’s as if science itself exploded in the modest room.

He moves to gather up the mess, but Eva stops him. “You don’t have that kind of time.”

“I don’t even know if I still have time,” he admits.

“Only one way to find out.” She draws a halting breath. “Come on.”

They get into the Honda Civic that Jonas rented solely for the purpose of traveling to the Spire. He drives. He’s never been to the Spire before but doesn’t bother with GPS. All he has to do is drive toward the giant needle piercing the earth. But as they pass over the Enko River, the Civic slows to a crawl. The street is choked off by traffic.