Let's Run an Experiment!

The reason that stick of gum caught my eye was simple — I'd seen it before.

Riding over on the electric bike, I'd even thought of the gum wrapper stuck to my face.

Back then, I was sure of it…

In the past, before Lee Soyeon's villa had even been built, I'd been chewing gum and half-heartedly stuck the wad to a scrap of paper.

Then I'd collided with some high school girl and dropped it. Looking at it that far, it might sound like I was overreacting over a piece of gum — except the brand I'd been chewing then was exactly the same as this one.

"Does that even make sense?"

The timelines were clearly different, weren't they? Even if the past changed, that should just spawn a new future branching off from it.

That was quantum mechanics. So the fact that the gum I'd thrown away was still sitting there meant… what, exactly?

Or maybe I was just mistaken. Was I being paranoid?

No. This was absolutely not something I could just shrug off.

Whether it was my imagination or the real thing — that was the question.

While I worked on the bike, I checked the gum again. Same brand as the one I'd been chewing right before I came back.

Two years later, there was no way it should still be here, right? Especially when this was from before construction even started.

Thinking about it coldly, the gum I'd dropped still being here was the strange part.

Pure coincidence, in other words.

Someone else's discarded gum just happened to stick there… That was the sensible way to look at it.

But if there was an effect…

If I dealt with zombies in this era, would the future feel it too? Would things change?

I'd figured quantum mechanics meant it wouldn't be a problem — but this left a weird taste in my mouth.

"Ah, I can't focus."

In the middle of fixing the bike, the thought that I had to settle this first kept pushing to the front.

No time to rest, either.

But how was I supposed to check? I needed proof.

I paced the yard, and then my eyes landed on ‍‍‌‌⁠​​⁠‌​​‍​​‍​‌​⁠‍‌‍⁠⁠‌⁠‌‍‌‍‌‌‌‍⁠​‌​‌​‌‍‌‌‌⁠‍​​‌‍⁠‌‌⁠⁠the scorch marks from when I'd burned the cleaning supplies.

The old lady had complained when I first arrived, but I'd bought the house outright, so that hardly mattered now.

Nobody was going to bother scrubbing the yard clean, so those marks would stay right where they were.

"…"

I stepped through the door to the future and looked at the yard two years from now.

"It's there."

The burn marks I'd left were still sitting in place. Blackened floor, just as I'd left it.

No — that alone wasn't enough. I needed more certainty.

Just to be sure, I came back to the present and deliberately scorched another spot.

Would this new burn mark exist in the future too? Heart pounding, I passed through the door again.

The moment I stepped past the front entrance and looked out at the yard, I saw two burn marks instead of one — and that was all the confirmation I needed.

It had an effect.

Traces of what I did in the past remained in the future.

So what the hell was I supposed to do now?

My head was starting to spin.

If I saved the present world, would that ripple into the ‍‍‌‌⁠​​⁠‌​​‍​​‍​‌​⁠‍‌‍⁠⁠‌⁠‌‍‌‍‌‌‌‍⁠​‌​‌​‌‍‌‌‌⁠‍​​‌‍⁠‌‌⁠⁠future world as well?

The timelines were clearly linked, but this was supposed to be quantum mechanics. So why?

I couldn't make sense of it, and my scientific knowledge was pitiful to begin with.

Thanks to that, I spent the rest of the day in a foul, tangled mood, and the next morning I was waiting for the remodeling contractors to show up.

"Goddamn it. I do not want zombies showing up in this world."

If I stopped them, would that hit the future world too? Then would the future world change?

I had no idea how any of it worked, and my skull felt ready to split open.

It was maddening. If the future changed, what about everything I'd already done?

I could feel my drive draining away. Would girls like Lee Soyeon and Seol-hwa — the ones I was having so much fun collecting — just vanish?

What about my revenge?

It felt like watching gold slip through my fingers right after I'd finally gotten a grip on it.

And if I failed to stop the zombies, this place would turn into an apocalypse too.

"Haa… my head hurts."

Even while I stewed, delivery drivers kept hammering on our front door.

Food, ‍‍‌‌⁠​​⁠‌​​‍​​‍​‌​⁠‍‌‍⁠⁠‌⁠‌‍‌‍‌‌‌‍⁠​‌​‌​‌‍‌‌‌⁠‍​​‌‍⁠‌‌⁠⁠convenience goods, even the shower booth I'd ordered earlier — all kinds of packages piled up in front of the house.

"That's a hell of a lot."

My head was too much of a mess to deal with it, so I left everything in the yard and went back inside for the moment.

"Wait… then is the stuff I left in the yard still there too?"

It hardly mattered at this point, but I went to the future to check anyway. Sure enough, there it all was — weathered by two years, but sitting pretty.

See? Connected after all.

I was just thinking how strange it was that everything had sat there untouched for two full years when a question mark lit up in my head.

It had been sitting there for two years? There was no way my predecessor wouldn't have used this.

Thinking about it, it was weird. One thing was certain: this connected semi-basement itself wasn't directly affected.

If it were, the predecessor's materials I'd brought into the world from two years ago would still be sitting here two years later. In other words, everything except this basement with the linked door was being influenced.

Shouldn't the predecessor have seen those goods out in the yard?

And if he had, a man thrashing to stay alive would absolutely have put them to use.

So why?

My thoughts tangled all over again. It was as if the predecessor had left it all alone — like it had never been there. Why?

Hold on. Come to ‍‍‌‌⁠​​⁠‌​​‍​​‍​‌​⁠‍‌‍⁠⁠‌⁠‌‍‌‍‌‌‌‍⁠​‌​‌​‌‍‌‌‌⁠‍​​‌‍⁠‌‌⁠⁠think of it, the electric bike I'd left in the yard was still there too, wasn't it?

Amazingly enough, my electric bike was sitting there after two years, rusted over.

I rushed back to the present — the past — and checked. A perfectly intact electric bike sat in the yard.

"…."

Startled, I took that electric bike and pushed it through the door to the future.

When I went out to the yard, the electric bike that had been there before was gone.

"It updates in real time?"

An object that had existed in the past had shifted along the timeline, so the electric bike on the future timeline disappeared.

That tracked. So what about the predecessor? He hadn't written a single word about any of this? I hurriedly left the electric bike in the present-day yard and dug through the predecessor's materials.

If he'd noticed any change in the yard, something should have turned up, right?

But there wasn't a single trace of it in the predecessor's records.

"Huh?"

Something was off. This didn't match the quantum mechanics or time paradoxes I knew.

Leaving all of it sitting there for two years was strange enough on its own.

A thought flickered through me — maybe this wasn't what I thought it was at all.

Some time later, two remodeling contractors showed up.

"Yes. We'll take a look and give you an estimate."

"I want it sturdy. Bomb-shelter grade. That's what I'm after."

"When you put in the request, asking us to build it like a survivalist's bunker was a pretty unusual order. It's going to cost a lot."

"I don't care."

I had money to burn. Hundreds of billions wasn't a joke.

"I'll pay whatever it takes. Build it so solid that even bullets won't leave a scratch."

"With enough money, anything's possible. But if we're doing a full overhaul, what about that semi-basement?"

The semi-basement? Absolutely not. If they so much as touched it during construction…

"Leave that alone. I'm comfortable down in the semi-basement. If you have to do something, just swap out the door."

Strictly speaking, this was still construction-level work. We weren't knocking the house down, but we were going to gut the interior and rebuild it from scratch. Swap out the interior materials and resurface the whole thing.

I spent over an hour going over the estimate with the remodeling guys.

"Material costs have gone up lately, though. Construction's going to run into the hundreds of millions. We'd have to rip out all the interior finishes and start over, you know? Honestly, at that point you might as well just build a new house…"

"Just do it."

Money wasn't the issue, so just get it done. Did they think I didn't know building new would be easier? Worrying over nothing.

I couldn't tear the whole place down because of the semi-basement. This was the best option I had.

It turned into a farce where I ended up talking the contractors into doing the job.

"All right. We'll draw up an estimate for this and come back."

After all that wrangling, the remodeling was finally going to move forward the way I wanted.

That was the kind of knowledge people who'd been burned by remodeling disasters passed around — but I had a more reliable method.

It would cost a bit, but the only safe way was to bring a lawyer into it.

And since money still wasn't a concern, all the better.

Either way, there was only one thing I needed to confirm. Whether this was a time paradox, quantum mechanics, or some mix of the two.

"Might as well take a few days off and figure this out."

I had a few more things to test. Objects were one thing — but what about people?

If I met someone from the past, would I still have that memory in the future world?

And if I built a structure the way I was doing now, how would it be perceived two years later?

I had to settle those questions. That was how I'd pin down exactly how this linked world interacted with me.

My feet carried me outside almost on their own. First stop: Lee Soyeon's villa — the place where I'd spat out that gum.

On the way there, I saw a lot of high school kids.

The time of day was still… whatever. Looks like they only had morning classes.

Those kids were free game if I felt like it. Just thinking that sent a pointless surge of lust through me.

I'd soothe Seol-hwa a little when I got back this time, then take her right away.

I was standing there with a stupid grin on my face when—

"What is this freak smiling about?"

A sneering laugh cut in out of nowhere, the kind designed to piss someone off.

Who the hell was that?

And they were pointing right at me while they laughed?

Right in front of me, two kids in school uniforms — high school girls, or maybe middle school, hard to tell — were snickering.

Were they out of their minds? Kids this rude actually existed?

I sighed, lamenting the lack of manners, when I heard boys' voices too.

Hold on. It wasn't even lunchtime yet and they were already out? Exam period, maybe?

That tracked. Hell… back when I had exams, I'd finish and head straight to the PC bang with my friends too.

Anyway, I gave the kids laughing at me a mild warning. This wasn't the future, after all.

"Kids, no matter how funny something is, you don't point at someone and laugh right in their face. Go a little farther away if you want to laugh."

I delivered the line calmly and started to turn away — then the cursing hit me.

"Hilarious. What a fucking loser."

What did they just say?

Weren't they a little too ill-mannered? And right in front of me, two boys were staring me down with a clear what are you gonna do about it? look on their faces.

Normally I would have let it go. At the bottom of society, pushing back only meant taking more losses. But things were different now.

"You shouldn't use that kind of language. Kids these days…"

"Yeah? So what."

One of the boys glared at me like it was the most natural thing in the world.

But that face looked familiar. Wait a second — no way.

"You. Are you Min Doyoon, by any chance?"

The long hair had been cut short, but those half-lidded eyes and thick lips still brought Min Doyoon to mind.

So this little shit was a thug. Bunching up with his buddies to pick fights.

"The fuck? How does some old man know my name?"

"It's on your uniform, dumbass."

I needled him on purpose, and Min Doyoon's face crumpled instantly. Quick temper on this one.

"Dumbass? Old man. You wanna get hit? Fucking adults, I swear…"

The pack closed in around me all at once. What a pain. High schoolers who couldn't get their heads on straight and spent their time playing delinquent.

No wonder he'd still be running a gang out of the auditorium two years from now.

A few of them were snickering as they came closer.

That was when I pulled out my phone.

"A whole group threatening one person… If this turns into a fight, you kids are the ones who'll catch more heat."

"Scared?"

Min Doyoon and one of the other boys started laughing.

"You scared? We ain't scared of that shit. Old man, let's go. One round."

A lightbulb went on in my head. What if I left Min Doyoon with a deep impression right here?

How would the future Min Doyoon react?

This was the perfect chance to run the experiment.

"Hey, you chicken? Not sayi—"

And then I grabbed Min Doyoon like lightning and body-slammed him in one motion.

"Aaaagh!"

A scream rang out, and the remaining boy stared at me in shock — so I threw a punch.

A clean, satisfying impact, and he hit the ground too.

"Kids. Don't run your mouths so freely."

But I couldn't stop there. The ones who'd egged them on needed a fair share of the lesson too.

I walked straight up to the high school girls and educated them with a slap across the face.

"We're sorry… We're sorry!"

Only after listening to the high school girls grovel did I turn and walk away.

Now I was firmly planted in their heads. I was looking forward to seeing how the future Min Doyoon would react.

And one more thing.

If my belongings were still in place two years later, that meant if I installed public restrooms and everything else I'd mentioned, they'd still be there two years from now too.

"I'm going right now. For the future's sake."

That day, tens of millions more won walked out of my wallet.