Time travel (2/2)
“Do you want to see the continuation of yesterday’s experiment?” Gu Yilan asked the boy.
Hearing that, Su Zesui nodded enthusiastically.
He had thought about the strange phenomenon that “observation changes the result” all night and had barely come up with a guess.
He asked the all-knowing Gu Yilan, “Is it that the detector affected the photons?”
The detector confirms that the photon’s path is determined through “particle collisions.” Since collisions are involved, it’s possible they might affect the photon and thus influence the final experimental results.
So, it’s not some abstract, subjective factor like “observation” that changes the outcome—rather, it’s the “particle collisions” that cause the change.
At least, this explanation makes the world feel a little less mysterious.
The moon won’t suddenly disappear just because no one is observing it.
As a physics PhD student, Gong Chuang was very familiar with experiments conducted by seniors in the field. When he heard the boy’s words, he instantly recognized which experiment was being referred to and couldn’t help but say, “You’re quite smart, kid.”
“Let’s go.” Gu Yilan unlocked the handcuffs from Su Zesui’s wrists, then glanced at Gong Chuang beside them. “Help set up the equipment.”
Gong Chuang, who was like a human light bulb and unpaid labor but still carried some guilt, clicked his tongue softly and reluctantly followed the young couple.
Gu Yilan held a lot of power at University A, allowing him to use the lab without going through a supervisor, which saved a lot of time on small experiments.
In physics lab A1055, upon hearing the name of the experiment, Gong Chuang took several instruments from the cabinet.
This experiment was almost the same as the one done previously at home, except it added an “eraser.”
The detector could obtain the photon’s path information, while the eraser could erase the obtained path information.
In the first experiment, photons individually passed through the double slits without observation, resulting in alternating bright and dark zebra stripes.
In the second experiment, photons passed through the double slits with observation, and the observation results were not erased. The outcome was two bright stripes.
Some said the change was caused by human observation, but Su Zesui believed it was the particle collisions from the detector that caused it.
In the third experiment, photons passed through the double slits, were observed, but then the observation results were erased afterward. Essentially, the photons were collided with particles twice, yet in the end, no path information was known.
Su Zesui held his breath, nervously waiting for the result.
Gong Chuang, already knowing the outcome, whispered to Gu Yilan, “Although our research is in this area, sometimes I still can’t understand why quantum entanglement even exists. Is it a bug in the universe?”
Gu Yilan glanced at him coldly and dismissively replied, “What God does doesn’t need to be explained to you.”
Gong Chuang: …
——Should’ve kept my mouth shut.
At that moment, Su Zesui finally got the result—
Contrary to his expectations, the pattern returned to alternating bright and dark zebra stripes! Despite two particle collisions from the detector and the eraser, the result was exactly the same as when there were no collisions at all!
This meant his earlier assumption was wrong: particle collisions don’t actually affect the experimental result.
After all, particle collision directions and speeds are extremely random and varied. It’s impossible that two collisions just happened to cancel each other out.
“Brother,” Su Zesui was completely stunned and looked back at Gu Yilan.
Gu Yilan dropped Gong Chuang and stepped forward. “It’s exactly as you thought. The only reason the experimental results change is because you are observing. It has nothing to do with any microscopic factors.”
“W-why?” Su Zesui didn’t understand. He looked up out the window. “Why does the moon always stay there?”
If microscopic particles change their behavior just because of his observation, why doesn’t the moon change just because so many people observe it?
Where exactly is the boundary between the microscopic and macroscopic?
Everything in the world is made up of microscopic particles. How many particles does it take for something to become macroscopic? Below how many is it still microscopic?
Su Zesui couldn’t help but think of the famous “Schrödinger’s Cat” experiment, which builds a bridge between the microscopic and macroscopic, producing the baffling half-alive, half-dead result.
“This relates somewhat to my research direction,” Gu Yilan said.
Su Zesui had good hearing and had overheard Gong Chuang earlier, so he quietly asked, “Quantum entanglement? Then… why entanglement?”
Gu Yilan shook his head slightly but explained, “I don’t study that. It hides secrets that humanity currently can’t understand, possibly related to wormholes that only exist in theory.”
Gong Chuang beside them: ???
——Who the hell just coldly told me to mind my own business about what God thinks? Hypocrite.
Gu Yilan ignored the irritated Gong Chuang and looked at Su Zesui. “Do you know about Hilbert space?”
Su Zesui was stunned. The familiar term sparked memories buried deep in his mind.
It was knowledge he had learned in university’s physics department before his time travel.
Su Zesui’s mind automatically constructed a multi-dimensional coordinate system, where macroscopic objects were placed within that framework—and its unit was… degrees of freedom.
He couldn’t help but think of Gu Yilan’s WeChat.
The man’s WeChat name was “11th Dimension,” and his status message read “Higher Degrees of Freedom.” Did it have something to do with this kind of space?
But the next second, Gu Yilan’s voice struck his mind like a heavy blow, shattering all his thoughts.
“This is a theory used to hypothesize the existence of parallel universes.”
“Pa–parallel universes?” Su Zesui’s eyes widened in shock.
“Mhm.” Gu Yilan raised an eyebrow. “Want to travel through time and space?”
Su Zesui stared blankly at him, fingertips trembling. He’d completely lost the strength to speak.
For some reason, his memory was poor in certain areas. If it hadn’t been brought up, he might’ve forgotten why he came to this world in the first place.
Gu Yilan hadn’t expected such a reaction from the boy and quickly dropped the subject. “Alright, for now these are just hypotheses. If you want to prove them, you need to first study hard for the Physics Olympiad — then look into this field later on.”
“Just a hypothesis?” Su Zesui mumbled to himself.
“Yes,” Gu Yilan replied.
Su Zesui puffed out his cheeks, still looking a bit nervous. He grabbed onto Gu Yilan’s shirt as if afraid the man would vanish like a zebra’s stripes—disappearing the moment he was observed.
Gu Yilan noticed something off in the boy’s expression. He let him tug on his clothes and quietly studied his face.
Gong Chuang chuckled. “What kind of reaction is this, kid? Scared stiff?”
He meant it as a joke—but to his surprise, Su Zesui nodded earnestly, face tight with tension, saying nothing.
Gong Chuang couldn’t help but laugh even more.
“Ready to go back and do your homework?” Gu Yilan asked, testing the waters.
Su Zesui gave a muffled “mm” in response and followed him back to the office. But he still couldn’t help asking again, “It’s really… just a hypothesis?”
Gu Yilan guessed the boy might be hoping to travel back in time to undo something painful—and he didn’t want to give him vague, baseless hope. So he said simply, “As far as we know, there’s been no real progress.”
Su Zesui felt a strange mix of emotions. He couldn’t even tell what he was feeling—but the tightness in his chest eased a bit after hearing that. At least now, he could breathe properly again.
He quietly cuffed himself, picked up a bag of chips, and took a bite.
Crispy. Delicious. Real. Not something that would vanish just because it had been observed.
Watching the boy’s distracted, out-of-sorts behavior, Gu Yilan—rare for him—added a few more words of reassurance: “No one truly understands quantum mechanics. Not even Einstein could. What matters is reality. Don’t fall into a void of nihilism. I’ll come get you later.”
Su Zesui felt comforted and nodded firmly.
After finishing the entire bag of chips, he felt much better.
This was a real world! His “time travel” had to be some paranormal phenomenon beyond current human understanding! As a time traveler, there was no way he’d get caught—and absolutely no way he’d be sent back to his original world!
With that shift in mindset, Su Zesui was no longer anxious. Instead, he just became even more attached to Gu Yilan.
That evening, after finishing his homework, he lay on the bed next to Gu Yilan—reading research papers with him while kicking his legs and playing on his phone.
Just then, he got a message from Brother Gong Chuang, who he’d recently added on WeChat:
[Brother Gong Chuang: Hi, Suisui. Are you coming to the lab again tomorrow?]
On the phone, Su Zesui didn’t feel as intimidated. His replies were still stiff and awkward, but at least he could hold a proper conversation now.
[(o^^o): Go.]
[(o^^o): Today’s experiment was really fun. I’ll go tomorrow to do homework.]
[Brother Gong Chuang: Actually, there’s also a version 2.0 of today’s experiment — the Quantum Delayed-Choice Eraser. I’ll have your Brother Gu Yilan take you through it.]
[(o^^o): Okay~]
After circling around with pleasantries and procrastinating from finishing his paper, Gong Chuang finally—sneakily—asked the one question that had been burning in his mind, but he never dared to ask Gu Yilan directly:
[Brother Gong Chuang: So… how far have you and Gu Yilan gotten? Can you tell this brother?]
It was that question again. Su Zesui paused, face serious, and gave it some thought.
He lifted his eyes and snuck a glance at the man beside him—leaning against the headboard, quietly reading academic papers on his tablet. Blushing a little, he typed:
[(o^^o): I marked him.]
[Brother Gong Chuang: ???]
——What the hell? Marked??
Sometimes, Gong Chuang truly felt like there was a massive generational gap between him and these new-age kids—he couldn’t even understand their slang anymore… So he could only gently probe:
[Brother Gong Chuang: You mean… physical contact?]
[(o^^o): Mmhm.]
Seeing the boy’s firm response, Gong Chuang sucked in a breath, torn between thinking Gu Yilan really is a beast and the faint hope that maybe—just maybe—the kid meant something different.
[Brother Gong Chuang: You mean… like, passionate, heart-racing, skin-to-skin, fully in-and-out kind of physical contact?]
Su Zesui recalled the moment in question, hesitated slightly, but eventually replied:
[(o^^o): Yes.]
[Brother Gong Chuang: Already??]
[(o^^o): Mmhm.]
Gong Chuang clicked his tongue and shook his head, silently cursing Gu Yilan as a complete bastard—but he still couldn’t resist gossiping a little more:
[Brother Gong Chuang: How did it feel?]
[(o^^o): Brother hurts a lot.]
Gong Chuang’s fingers suddenly froze on his keyboard. He stared at the boy’s reply on the chat screen, a long string of ellipses typed out, his brain feeling like it had just exploded into fireworks.
What type of question is this bro? What the hell