What is a half-life?

Half-life is a game developed by a binary-brained fatty… no, wrong.

Half-life is the time required for half of a radioactive element’s atomic nuclei to decay. Using carbon-14’s half-life to determine historical dates is a common archaeological research method—by measuring the decay content of radioactive elements, one can determine the age of target objects.

It sounds sophisticated and seemingly unrelated to ordinary people’s daily lives, even more disconnected from Bai Yang, an ordinary high school student. What connection could we common folk, living our simple lives, have with radioactive isotopes? What could we have to do with half-lives?

We do—please raise your left hand.

Roll up your sleeve.

Look at your watch face in the dark—if you’re an old per… gentleman with a vintage luminous watch, its dial is coated with a common radioactive isotope.

Tritium.

Bai Yang gave up on sleep entirely, immediately climbing out of bed and pulling out his phone to open Taobao.

With the almighty Taobao’s help, there was nothing that couldn’t be bought.

Tritium tubes!

Tritium tubes are common luminous tubes, fully sealed in glass, ranging from a few millimeters to one or two centimeters in length. The inner walls are coated with phosphorescent powder, while the inside is filled with tritium, a radioactive isotope of hydrogen. The dilute tritium gas has weak radioactivity, exciting the phosphorescent powder to glow. These are commonly used in luminous watches, military compasses, and gun sights, and sometimes by die-hard fishermen as float indicators.

Tritium has a half-life of twelve years, meaning half of a batch of tritium elements will die in twelve years. A tritium tube’s brightness will halve in twelve years and nearly extinguish after twenty years.

Perfect timing!

The tritium tubes would be perfect as time markers.

Bai Yang planned to buy two brand new tritium tubes on Taobao, then find one five-year-old tube and one ten-year-old tube on Xianyu. Two new, two old—but since none had reached their half-life, all four tubes would still be glowing.

This was his plan:

Arrange all four tubes with UV glue in a transparent plastic box, ordered as new, five-year, ten-year, and new. After BG4MSR dug up the time capsule, Bai Yang would have her find the time marker inside and describe the tubes’ luminescence—if all four tubes were glowing normally, unchanged from when he buried them, then she was lying.

All that talk about the apocalypse and 2040 would be nonsense.

If all four tubes barely glowed in the darkness, it would prove the girl was telling the truth, and time had indeed passed at least twenty years.

If the five or ten-year tubes were dark but the new ones still glowed, it would prove BG4MSR lived in the future, but she had miscalculated her era.

Bai Yang believed there could be no more solid, irrefutable proof than this. This was using pure force to overcome trickery, grasping the essence, and pointing directly to the truth, without any twists and turns or fancy tricks. Even if she were James Bond, 007, or a master thief with a thousand ways to secretly dig up the time capsule, check its contents, and bury it back perfectly without a trace, she couldn’t alter the tritium tubes’ luminescence results.

And as long as he didn’t reveal beforehand that it was a time marker or that they were tritium tubes, she couldn’t possibly know what they were, much less lie about them.

Using forces beyond human manipulation for verification eliminated all possibility of fakery and lies.

This was Bai Yang’s method.

I’ll bury the tritium tubes here, come on!

I’m not afraid of whatever methods you use, do whatever you want. Once you’ve opened the lid and looked, I’ll know if what you’re saying is true or false.

Order placed!

Thirty yuan each, sixty yuan for two tubes.

His wallet would hurt for quite a while again.

But Bai Yang was eager to try. As a high school student who had always followed the rules and studied properly from childhood, he rarely had the chance to do something so bold, absurd, and unconventional. Yet Bai Yang grew increasingly excited. His life, bland as plain water, had finally been touched by a different color. In novels and movies, this was often the opening of a grand adventure. He couldn’t fall asleep until three in the morning, his mind full of his plans, resulting in oversleeping the next morning.

Ban Xia put down her headphones and microphone, slowly laying her head on the desk.

What did he mean?

He could help provide evidence? Help prove it was 2040?

But hadn’t he claimed to be living in 2019?

How could someone living twenty years in the past help her?

The girl’s cheek pressed against the cold wooden desktop. Her right elbow propped on the table, her index finger dangling an amulet that swung gently like a pendulum—it was the coin her teacher had left her, with a hole drilled through it and threaded with a red string, which she could wear around her neck. Ban Xia’s gaze followed the swinging coin back and forth, utterly puzzled.

A chubby plastic desk lamp sat beside Ban Xia’s head, the room’s only light source. The light illuminated the girl’s face while her body sat in darkness. She liked to think in the dark; the quiet night helped keep her mind clear.

How would he provide evidence across twenty years?

Bury it? Hide it? Then wait twenty years?

Ban Xia easily thought of this possibility. He lived twenty years ago—assuming he did live twenty years ago (actually Ban Xia didn’t believe it either, but she had no choice)—then he could dig a hole in that era, bury whatever he wanted to send, then use the radio to tell her where to dig it up.

If she could find it, it would prove everything was real.

He would know she lived in 2040.

She would confirm he lived in 2019.

It sounded wonderful.

Ban Xia stared at the red string and coin hanging from her finger. The coin gradually lost momentum from friction, its swing getting smaller and smaller until it stopped, slowly rotating around the string’s axis, twisting it into a double helix.

It sounded reasonable, but her teacher had said that what sounds right and what looks right are different things, and what looks right and what works are different too. To judge whether something is feasible, ears alone aren’t enough—you need to engage your ears, eyes, hands, and brain all at once.

The girl’s brows slowly furrowed; she had a vague worry.

If he meant to do this—intended to send something across twenty long years to reach her hands—then this probably wouldn’t be a simple matter.

Once there’s a purpose, obstacles naturally follow. This world always leads you unwittingly to destinations you don’t want to reach while setting up countless barriers before your intended goals.

It definitely—definitely—wouldn’t be as easy as imagined.