3:59

THIRTY-FIVE

5:47 P.M.

PENELOPE PUSHED THE BOOK AWAY AND SANK her head into her hands. “Which still doesn’t explain exactly how the portal was created.”

Josie and Penelope had been at it for well over an hour, poring over a variety of books as they searched for anything that might explain how the portal had opened between Jo’s and Josie’s worlds. They’d covered everything from theoretical extra dimensions to pseudoparanormal studies, and still nothing quite explained the flash, the mirror, and the portal that opened every twelve hours.

Madison had been quiet, flipping through the discarded books, but she was far from disinterested. She watched Josie closely, listened to every word that came out of her mouth, and Josie couldn’t help but wonder if her reticence to believe Josie’s story had faltered in any way.

“Okay,” Josie said, closing the book in front of her. “Let’s start crossing things off the list, at least.” Her mom always taught her that when faced with a seemingly unanswerable problem, the best tactic was to eliminate impossible answers first, and whatever you were left with, however improbable, had to be the truth. She picked up a book on time travel and chucked it onto the sofa. “It’s not a time loop. Our worlds are too dissimilar to be replaying themselves.”

“Right.” Penelope grabbed two more books and walked them over to the sofa. “I don’t think it’s a holographic multiverse either. Same reason: our worlds are too different.”

“A what-what?” Madison asked.

“It’s a theory of parallel universes,” Josie explained. “Based on the holographic principle. Meaning that every universe has a mirror image, exactly the same in every way.”

Madison stood up and stretched her arms over her head. “I swear you two are speaking a foreign language.”

“We are,” Penelope said. “It’s the language of geek.”

Madison laughed weakly. It was the first time Josie had seen Madison let her guard down since they’d met. The harsh lines around her nose and jaw softened and Josie noticed the heavy circles under her eyes and the deep sagging at the corners of her mouth. The bitch-on-wheels attitude melted away and Josie saw a sad, exhausted girl.

Madison caught Josie watching her and turned quickly, but in that instant Josie had seen something else reflected in Madison’s light brown eyes: fear.

She wandered over to the kitchen and opened the door to the mini fridge. “Dammit,” Madison said. “Someone ate the half a sandwich I had stashed in here.” Madison slammed the door. “I swear those boys will eat anything that’s not nailed down.”

Josie smiled. “Yeah, that sounds like Nick.”

“Oh please,” Madison said with a snort. “You barely know him.”

“And you know him better?” Josie asked. She was pushing, she realized immediately, to see if Madison would spill the exact nature of her relationship with Nick. She was desperate to know, even though she kept trying to remind herself that it didn’t matter. That her attraction to this Nick could never amount to anything. Still, she wanted to know what had happened between them. But before Madison could say another word, Penelope steered them back on course.

“I’m going to cross all the objective collapse theories off the list as well,” Penelope said pointedly, still focused on the pile of books in front of them. “Since there’s no way we can prove the Penrose Interpretation.”

Josie sighed. “You would say that.”

“What do you mean?” Penelope’s eyes pinched together. She looked hurt.

“Sorry,” Josie said. “I’ve just heard it from you before.”

“Huh?”

“Back home. We’re lab partners and we’re doing our end-of-year project on the Penrose Interpretation.”

Penelope arched an eyebrow. “I let you talk me into attempting to prove an unprovable theory? What the hell is wrong with me over there?”

“It’s not unprovable,” Josie said. Why did everyone keep telling her that?

“Okay,” Penelope said. “But even if it’s true, it doesn’t explain how you’re here. Superposition collapses at our mass.”

“Fine.”

Madison popped open a soda and rejoined them at the table. “Superposition? Is that like a superhero thing?”

“Quantum superposition,” Penelope explained, “is the theory that a particle like an electron exists in all of its many property states simultaneously. But when you try to measure it, you only get one reading.”

“Oh, I see,” Madison said. She clearly didn’t. “So where does that leave us?”

There were two books left on the table. Josie picked up one in each hand. “Brane multiverses and quantum gravity.”

Penelope stifled a yawn. “So it must be one of them.”

“I haven’t read much on brane multiverses,” Josie said, turning the book over in her hands.

“The core of the theory is that universes exist on these thin planes,” Penelope said. Even though she was tired, she spoke quickly and her voice had a lifted inflection that Josie recognized. The science excited her. “An infinite number of them all existing very close together, but never intersecting. Some of them would be completely unrecognizable; some of them would be exactly like our own world. And everything in between.”

Josie nodded. “Common multiworld theory.”

“Right.”

Josie skimmed through a chapter on phase shifting of brane multiverses. The idea was that these branes overlapped in space-time with a dimensional phase shift, which meant Jo and Josie and an infinite number of their doppelgängers could have been moving through the same space but on different planes of existence—literally out of phase—in their respective parallel dimensions, and totally unaware of each other. In theory, it could describe how their two worlds—and the people in them—existed. But how the portal was created between them? That was something else entirely.

Josie flipped through the pages when something caught her eye. “‘While the branes overlap without connection between them,’” Josie read out loud, “‘if the gravitons are disrupted from the brane on which they exist, they could attach themselves to another brane in close proximity.’” She looked up sharply. “So gravitons could connect two branes?”

Penelope slid the book over. “Looks like it,” she said after reading a few pages. “It would take a massive subatomic explosion, but two universes could become attached to each other at a single point in space-time.”

“A massive explosion like creating micro black holes using ultradense deuterium and controlled fusion?” Josie said.

Penelope’s eyes grew wide. “Whoa. Does that work?”

“Yeah. Yeah, it does.” Josie gazed at an illustration of a graviton connecting two brane universes. “The gravitons are the portal, the stuff that connects our two worlds. They’re what’s holding our universes together.”

“So all we have to do is re-create the explosion,” Penelope said, “and we’ll have ourselves another portal.”

“One problem,” Madison said. “That explosion you’re talking about killed Nick’s brother. So unless you want to go down in a blaze of glory . . .”

Josie slumped back in her chair. “We’re right back where we started.”