Kevin sat back and stared. "You're serious? The wallpaper changed?"
"It never changed," Eddie said. "It had always been orange and yellow flowers. Tim agreed. He'd lived in that apartment for five years, and he claimed he'd been thinking about hanging different wallpaper from the day he moved in. He never did."
"And yet, the picture was of completely different wallpaper," Kevin said.
"Yeah, and I don't understand how that's possible. Tim and I must have discussed it—speculated about it. I can't remember."
Kevin stood up from the table. He paced back and forth, his fists clenching and unclenching as he moved. "Okay, this is a lot to take in."
"I'm not sure I understand," Ruby said. "Eddie almost sent a rat with a picture through the time portal, but he stopped it before it went through. And because he did that, the wallpaper changed? How does that make sense?"
"He did send it through," Kevin said, staring at the floor as he pivoted and turned to continue pacing.
"But I didn't," Eddie said.
"But you did. The rat walked through, but then you negated that action. The rat both walked through and didn't walk through. And... Holy God! What does this mean for temporal continuity. What do we know? How can we assume anything we remember is real?" He stopped pacing and stared at Eddie and Ruby. "We're wading into the deep end of the Twilight Zone, my friends."
Bryce had been listening, leaning against the wall. "You're saying that the result of a paradox is that things change."
Kevin threw up his hands. "What are the consequences of a paradox? Can you tell me? It's not hard to think up a paradox. Go back in time and kill your own mother before you're born—that kind of thing. We know what a paradox is, but we don't know what happens when you cause one."
"Redecoration?" Bryce offered.
"That's just what you can see. That's just what Eddie noticed in his photo. But what else changed? How much of the world changed because... because..." Kevin closed his eyes and threw his head back. "Because spacetime was damaged."
He pointed an accusing finger at Eddie. "You said you remembered the wallpaper with flowers. You said it had been that way for years."
"So the differences that your little stunt produced had an effect that stretched back in time." He frowned. "How is that possible?"
Nobody said anything for a while. Eddie twiddled his thumbs.
"The last time we talked about what happened to the world," Ruby said to Kevin, "You said you suspected we were dealing with some kind of... what was it? A multiverse collision or something?"
Kevin nodded. "I did say that. It felt like a cop-out explanation at the time because it didn't mean anything. But maybe it does mean something."
He pulled a notepad from a shelf and laid it on the table. He drew parallel lines with arrows. "The idea of a multiverse is that we have many different universes running parallel. They may be similar. There may be an exact copy of you that's done everything you have done, except you wore a brown shirt on Thursday and in the other universe, you wore a pink shirt. In another universe, dinosaurs still walk the earth. It's all speculation, but it fits with some branches of quantum theory."
He drew a scribble on one of the lines. "Now let's say you disrupted the flow of space time with a time machine—cause a paradox. You've put a tear in reality itself. What does that do?" He expanded the scribble until it crossed another line. "What if two separate realities collide. In one reality, your wallpaper is flowered. In another, it's got bananas. In one reality, Alexander Hamilton was never president..."
"Alexander Hamilton was never president," Bryce interrupted.
Kevin pointed at him. "See? So in your reality, Alexander Hamilton was never the first president of the Federate States of Columbia."
"Uh," Bryce said.
"So you send a rat through a time machine. It walks two seconds into the past, but then you stop it. Boom! Paradox. But just a little paradox. You don't even notice the difference. You just feel something is wrong."
"That doesn't explain why the world is so screwed up," Bryce said.
"But it does. It completely does, because it wasn't just a rat that traveled through time." He pointed at Eddie. "He did it too."
"But why should it be so different for me?" Eddie asked.
Kevin knelt beside the table and ran his hands through his hair. "I'm assuming Tim made a bigger time portal for you. Tell me, did he darken the portal for you as he did for the rats?"
"What does it matter?"
Kevin let out a little laugh—one that almost sounded maniacal. "It makes all the difference."
"I don't remember walking through. But Tim mentioned that it took a lot more calibration to keep the surface of the portal dark. There's a chance he didn't do it when I walked through."
"So as you walked through the portal, you saw yourself on the other side before you walked through. But unlike a rat, you knew what you were doing. You knew why you'd see yourself there, and seeing yourself didn't stop you. You continued through the portal."
"If he went through the portal," Ruby said, "And if nothing stopped him, then there wouldn't be a paradox."
Kevin stood up and stepped back. He looked frantic now, his eyes darting back and forth, thinking of the possibilities. "Don't you see? Seeing himself on the other side would create an infinity of paradoxes."
They all stared at him. "Not sure I get it," Bryce said.
"Okay, okay." Kevin waved his hands. "You begin walking through the portal and you see yourself already on the other side. What must that have been like? And once you see yourself, you might hesitate. You might speed up. You might gasp. And then you walk through with the memory that you saw yourself. You behave differently. You might turn back and try to see yourself. You might run screaming for the bathroom to puke. You might do a dozen things."
"I still don't see the problem," said Bryce.
"It's not a problem until you think about the recursive effect. It's cause-and-effect a billion times over. I mean, a billion isn't even close. You have a closed loop of action-and-reaction that doesn't happen over and over. It's all happening at the same time. An infinite number of reactions to an infinite number of causes. Tim may have thought he was playing it safe when he programmed his time machine to only go back two seconds in time. What he'd really done was create a reality bomb."
Kevin returned to the table, took his marker and scribbled all over the paper, slashing through all the timelines. "An infinite paradox that affects not just your reality, but every reality. Is this the kind of thing that caused the big bang? The universe might have blinked out of existence when you walked through. You created a temporal singularity that damaged many realities. Maybe all of them. Who knows?"
He tore the paper into strips, then smaller and smaller pieces and threw them in the air. He laughed again, pointed out the window and grimaced. "Look at the result. Outside, a million different realities have fused together. And it's all because you walked two seconds into the past and saw yourself there."