On Hourai Island, it wasn't just Jin who spent his time in exploration; the members of the Jin Family were also free to pursue their own research.
The themes for such studies were truly infinite.
The more knowledge they accrued, the more they realized how much the world was brimming with mysteries.
Lately, Hanna had been investigating one of the enigmas surrounding the Warp Gate.
She was eighteen now, a young woman in the bloom of youth, but her intellect was likely among the top five on Planet Ars. While she might not have been a match for the magi-brain Laojun in terms of pure logical progression, her flexible thinking was undoubtedly superior.
The mystery she was currently investigating was why teleportation succeeded when the destination contained gas, but failed when it contained a liquid or a solid.
Laojun operated a transporter. This was a magi-device designed to send objects to specific coordinates, but if a solid like a rock occupied those coordinates, or if they were underwater, the transport would fail.
However, that was not the case when the destination was filled with gas.
"Hmm, I wonder why that is?"
With Jin's permission, Hanna had enlisted Laojun's cooperation. Only Laojun could operate the transporter.
"Laojun, right now you check the destination with the Peeper before you send anything, right?"
"Yes, that is correct, Hanna-chan."
"So, you never really have transport failures to begin with... but hey, Laojun, being called 'Hanna-chan' is a bit embarrassing these days."
"But is Hanna-chan not Hanna-chan? Years ago, when I tried calling you 'Hanna-sama,' you told me to stop using such a formal title, did you not?"
"Well... yes, I did. But could you at least use 'san' instead?"
"Hanna-san, is it?"
"Yeah....Actually, that sounds a bit weird too. Oh, whatever, call me what you like."
"Very well. Then, Hanna... san, why don't we delve deeper into the differences between gases, liquids, and solids?"
"Hmm, let's see..."
Hanna pondered.
Teleportation and transport both involved moving an object to its destination via subspace or hyperspace.
The time required for the transit was exactly zero seconds. From this, one could infer that the flow of time in subspace or hyperspace was different from the space they inhabited—no, that wasn't quite it.
Time simply did not pass for the object during transit.
This had been proven by teleporting a clock. In other words, movement through subspace or hyperspace was instantaneous.
That likely meant that mass became zero within subspace or hyperspace.
"I believe that inference is correct, Hanna-san," Laojun said, supporting her reasoning.
"If that's the case, then mass—one of the fundamental properties of matter—is a physical quantity unique to three-dimensional space."
"Indeed."
As an aside, this specific discussion with Hanna would later prove invaluable when discovering the method to send Jin from the future back to the past.
"So, when returning from that space to this one, there must be a condition that prohibits the presence of liquids or solids."
"That would follow, yes."
Just as the discussion was reaching its peak.
"Hanna-chan, lunch is ready!"
Elsa's voice called out to her.
"Ah, is it that time already?"
One of Hanna's special talents was her ability to switch her thoughts instantly. Even in the middle of a deep realization, she could easily pivot to a different topic if necessary. Then, she could return to her original train of thought later as if there had been no interruption at all.
"I'm so jealous of Hanna," Jin had once said—he was the type to lose all track of his surroundings once he started focusing on a single task.
＊ ＊ ＊
"That was delicious."
"I'm glad you liked it."
"Hey, Elsa-onee-chan. What is Onii-chan up to today?"
Hanna asked about Jin's whereabouts, as he hadn't appeared for lunch.
"Mmh. He took Yuu and Mio to the Nord Federation. Right now, it's just you and me on the island."
"Oh, I see."
"Hanna-chan, how is your research going?"
"Hmm, it's difficult."
"...Was it, 'Why does it fail if there's a liquid or solid at the teleportation destination?'"
"Yeah, exactly."
"...I'm afraid I can't think of anything helpful. I'm sorry."
"No, Elsa-onee-chan, it's fine. This is something I need to figure out myself."
"Do your best."
"Thanks!"
＊ ＊ ＊
After lunch, Hanna returned to her discussion with Laojun.
"Hey, Laojun, I just thought of something. Earlier, we assumed that an object's mass becomes zero while moving through subspace, right?"
"Yes, that was our hypothesis."
"That matter then returns to this world... to 'normal space,' and the transport or teleportation is complete."
"Correct."
"So, it transitions from zero mass back to its original mass. It 'emerges' into normal space in that state, but..."
Hanna gave a clever grin.
"I don't think it can push away things that are too 'heavy,' can it?"
Hanna's theory was that because the mass had not yet fully returned to its intrinsic value—or was in the process of returning—it couldn't "push aside" something too heavy at the destination.
"Solids are out of the question, but even with gases, I bet you couldn't send something into a place filled with a very heavy gas, right?"
"I see. That is a plausible hypothesis. I believe we can verify this with an experiment."
And so, they began.
They generated a physical barrier and filled the interior with high-temperature, high-pressure air: 100 atmospheres at 1,000 degrees Celsius. While the temperature seemed excessively high, they had simply bypassed the effort of accurately calculating the exact point where air would maintain its gaseous state under such extreme pressure.
Laojun attempted to transport a small piece of adamantite into the chamber.
"...It failed."
The fragment did not transport.
"...Just as I thought."
They also tested steam—a state where water particles were scattered through the air—and the transport succeeded.
"It seems your hypothesis was correct, Hanna... san."
"Yeah."
In short, if the resistance at the destination was too high, the transport would fail. While the term "air resistance" wasn't technically precise for this phenomenon, it was close enough for their purposes.
"Which means the Warp Gate is safer, right?"
Since the Warp Gate used a physical housing, the interior could be protected by a barrier.
"True. Provided there are no foreign objects inside the exit housing."
It turned out the Warp Gate possessed advantages that the transporter lacked.
＊ ＊ ＊
That night, when she reported her findings to the returned Jin...
"That's incredible, Hanna!"
Jin praised her without reservation, his joy plain to see.
"Ehehe, thanks!"
Hanna beamed, her smile identical to the one she had worn the very day she first met him.