The day after the experiment, Ethan noticed something strange happening to his memories.
He could vividly recall studying at NYU, those memories felt as real as if he'd lived them himself. Yet he also knew with absolute certainty that he'd never left Harborview. Both sets of memories coexisted in his mind, completely separate from one another, like watching two different versions of the same movie.
Mason was experiencing the exact same symptoms. They started sharing a notebook, documenting all the "extra memories" that had suddenly surfaced.
"I have a memory from the summer of 1999," Mason wrote in the notebook. "I spent three sleepless nights in the hospital hallway while my dad was undergoing treatment. In the end, I gave up my dream of studying computer science and applied to NYU."
Ethan wrote the corresponding memory next to it: "Summer of 1999. My dad's company won a big contract. Our whole family went on a trip to Hawaii for a week. Standing on the beach, I made up my mind to become an engineer."
They kept writing, and soon realized that every major decision they'd made after their divergence had an exact opposite counterpart in the other's world.
The most bizarre part was that as they wrote down these memories, the images in their minds became more and more vivid. It was as if the very act of writing was solidifying these "possibilities" into something tangible.
"Memories have mass," Dr. Zhou explained over the phone. "Our latest theory suggests that when parallel universes begin to merge, information is exchanged before matter. What you're experiencing right now is the 'preliminary fusion' of memories."
"What will happen in the end?" Ethan asked.
"If the fusion continues, the two of you might... become one person. Not in the literal sense of merging into a single physical body, but rather as a superposition entity with two complete sets of memories. Like Schrödinger's cat—both alive and dead at the same time."
"What about the world?"
Dr. Zhou fell silent for an even longer period. "The world will also become a superposition state. Two versions of history existing simultaneously, two versions of the city coexisting, two versions of... everything."
Just then, an emergency news bulletin flashed across the TV screen: "Spatial overlap" phenomena were being reported across the globe. In Berlin, a church that had been destroyed in 1950 had reappeared, standing side by side with the modern commercial building that now occupied its original site. In Tokyo, a street that didn't exist on any map had suddenly materialized, its pedestrians dressed in clothing from the 1990s.
The world was splitting into two—or rather, two worlds were merging into one.