That night, Bai Yang lay in bed unable to sleep.

He hadn’t been able to sleep well these past few nights.

Today was September 29th. Tomorrow was the last working day before the National Day holiday. The day after tomorrow, the holiday would begin. Despite being third-year high school students, the Education Bureau had given them a full seven-day holiday and strictly forbidden any supplementary classes.

There was no moon tonight, and it hadn’t cleared up after the rain. The air conditioner unit mounted outside hummed steadily, with the indoor temperature set to 25 degrees Celsius. Though not hot, the air felt stuffy, probably due to the doors and windows being closed too long, causing carbon dioxide levels to rise. Bai Yang took a deep breath, resting his hand on his forehead.

He wore a white short-sleeve T-shirt and black shorts, one leg bent, his body sprawled motionless on the bed while his thoughts wandered freely.

Once the tritium tube arrived tomorrow, he could start making the time marker, stuff it into the time capsule, and bury it in the lawn by the community square.

Where should he bury it?

Bai Yang sketched out the layout of Meihua Villa’s community square in his mind.

That square was huge.

For something as small as a twenty-centimeter-long time capsule, if he just buried it anywhere, they’d need an excavator to plow up the entire ground to find it.

If she had a metal detector, it would be easier – like the mine detectors used by Japanese military engineers in war movies about mine warfare, sweeping across the ground like a lawn mower, beeping when it found mines. The principle was simple electromagnetic induction. If the girl had a metal detector, she could sweep the lawn and find the time capsule he buried.

Of course, she might also dig up unexploded mortar shells.

So he needed a marker.

Behind the bench?

Or under a tree?

Bai Yang pondered. Without question, the marker was important, but he couldn’t bury the time capsule somewhere too obvious where it could be easily found, since it needed to stay safely hidden for twenty years.

If hidden in too easily discoverable a place, who knows when some random person might intercept it?

The great catastrophe that would destroy human civilization – how chaotic would the world become? Bai Yang couldn’t even imagine.

He decided to scout locations tomorrow during the day, finding several backup spots. The location needed to meet these conditions:

First, concealment.

It couldn’t be discovered by anyone during the twenty years.

Second, safety.

It couldn’t be lost or damaged in the disaster.

Third, ensure the other party can find it.

So it needed precise coordinates so that even after twenty years, the other party could locate the burial spot based on the coordinates.

Once he buried the time capsule, he would tell BG4MSR the location and let her dig it up.

Bai Yang let out a long sigh.

This was interesting.

Could radio waves traverse time? The 14.255 MHz shortwave from the ICOM725 radio – -light was also electromagnetic waves, could light cross time?

Perhaps light could cross time. On any starry night, open your eyes and look up – the entire sky you see is ancient.

To you, they are the past; to them, you are the future.

But could you talk to them in real time?

Could the future and past communicate in real time?

His physics teacher would be pounding his coffin lid: Impossible! Information can’t travel faster than light!

Bai Yang rolled over on his physics teacher’s coffin lid, lying on his side, gazing at the black old Icom725 on the bookshelf. People often said it was just a radio, and truthfully its structure wasn’t much more complex than one – a radio’s core was just a simple LC oscillation circuit, and an LC oscillation circuit consisted of an inductor and a capacitor. You could buy a handful of inductors on Taobao for two yuan, and capacitors even cheaper. Connect these two things in series and you get a high-frequency oscillating current. Sets like the 725 that used quartz crystals were even simpler – crystals oscillate when electrified, like He Leqin stepping on an electric pedal, except He Leqin vibrated a few times per second while crystals vibrated millions of times per second. The high-frequency oscillating signal then went through an amplifier and antenna to be transmitted – that was the principle of radio transmitters… Such a simple structure, saying it could traverse time was like saying you could build a spaceship with wooden boards and nails.

Many things in this world that seemed profound and mysterious, once you peeled away their shells, turned out to be just amateur operations.

Bai Yang rolled over again, lying on his back and staring at the ceiling.

The room was very dark. The white bedroom ceiling could no longer diffuse enough light into Bai Yang’s eyes, so to him, it wasn’t white, but neither was it black. Like the view after closing your eyes, you could hardly call it any color – it was blurry, dim, seeming to jump like static on an old black and white TV.

Bai Yang pulled out his phone from under the pillow and turned on its flashlight toward the ceiling.

The bedroom suddenly lit up, a huge white spot on the ceiling. Now the light’s path was clear and traceable. Bai Yang thought about radio waves’ transmission path – radiating from the radio’s antenna, traveling up dozens of kilometers to hit the ionosphere, then being reflected down – just like the flashlight in Bai Yang’s hand now, light emitting from the LED, traveling up to hit the ceiling, then being reflected into a pair of open eyes-

The girl blinked.

Ban Xia lay on her back, staring blankly at the white light spot on the ceiling.

She waved the small lamp in her hand, and the light spot on the ceiling followed her movement. This game was honestly quite boring – she wasn’t a cat, not interested in moving light spots.

But she had nothing else to do.

Couldn’t sleep at night.

Ban Xia rolled over to lie on her stomach, wearing a white tank top and black pajama pants. She hugged her pillow and buried her face in it, then raised her legs to kick the bed board repeatedly, kicking hard with a “bang bang” sound.

After a few minutes, she stopped moving, lying stiff on the bed, face buried in the pillow like a corpse.

So annoying.

Tomorrow – or the day after at the latest – BG4MXH would tell her where to dig for treasure.

Would this plan work?

So annoying, so annoying, so annoying, so annoying.

If it didn’t work, she’d have his head!

Hmph!

Ban Xia raised her hand and made a slashing motion in the air.

No good, he was the only person who knew about her. If she lost this one, where would she find another?

So Ban Xia reached out both hands and virtually put his head back on.

It really must be her period coming – she usually wasn’t this agitated. Ban Xia lifted her face, let out a long sigh, spat out the hair in her mouth, and then rolled onto her back, holding the lamp in her hand.

She pressed the lamp switch rhythmically, making the light flash.

The teacher had taught Ban Xia how to send CW amplitude reports, that is, Morse code, but Ban Xia wasn’t very proficient as she rarely had to use it.

Long-long-short, ta-ta-di.

“G,” Ban Xia recited in her mind.

Long-long-long, ta-ta-ta.

O.

Long-long-long, ta-ta-ta.

O.

Long-short-short, ta-di-di.

D.

“Next is…”

Short-long-short-short, short-short-long, long-short-long-short, long-short-long.

LUCK.

“Good luck.”

Short-short-short-short, short-long, short-long-long-short, short-long-long-short, long-short-long-long.

“Happy.”

Ban Xia traced two short arcs with her finger in the darkness, then added a long arc, forming a small smile.