"What happened with that thing?"
Riku asked Aoi as soon as he entered the club room.
"It went well."
"Good."
Yuki looked puzzled. "What are you talking about?"
The two laughed simultaneously.
"It's long to explain," Aoi said. "But this is exactly conversation compression."
"Compression?"
"Yes. Between Riku and me, there's shared context. 'That thing' gets through."
Yuki opened her notebook. "Is shared context an information theory concept?"
"Precisely, it's related to Kolmogorov complexity," Aoi explained. "Message length depends on receiver knowledge."
Riku gave an example. "If I say 'continuation from yesterday' to Yuki, you understand, right?"
"I do. But to outsiders, it's meaningless."
"Exactly," Aoi nodded. "Compression ratio is proportional to shared knowledge amount."
Yuki thought. "Then the closer people are, the fewer words needed?"
"Yes. Between lovers, sometimes just eye contact gets through."
"Ultimate compression," Riku laughed.
Aoi drew a diagram on the whiteboard.
"Information amount = Message length - Shared knowledge"
"The more shared knowledge, the shorter the message can be."
Yuki understood. "That's why experts can converse with just technical terms."
"Exactly. Technical terms are labels that compress vast concepts into one word."
Riku asked. "But if you compress too much, it doesn't get through?"
"Correct," Aoi acknowledged. "Optimal compression ratio is determined by the other person's knowledge level."
"The essence of education."
Yuki thought of another example. "If I say 'school', everyone can imagine something."
"But what they imagine differs by person," Aoi pointed out. "That's the limitation of compression."
"Perfect restoration is impossible?"
"Generally impossible. That's why misunderstandings occur."
Riku became serious. "Then how do we prevent misunderstandings?"
"Add redundancy," Aoi answered. "Important things are conveyed multiple times, in different ways."
"Isn't that inefficient?"
"It's a tradeoff between efficiency and certainty," Aoi explained. "Higher compression is efficient but increases error risk."
Yuki summarized in her notebook. "High compression: efficient but risk of misunderstanding Low compression: redundant but certain"
"Good organization."
Riku looked out the window. "Human relationships might also be measurable by compression ratio."
"Interesting perspective," Aoi showed interest.
"With people we meet for the first time, we speak politely with low compression. As we get closer, high compression works."
"True," Yuki agreed. "Building trust can also be called increasing shared knowledge."
Aoi supplemented. "And that shared knowledge makes communication more efficient."
"It's circular," Riku noticed. "Communication → shared knowledge → more efficient communication"
"A positive feedback loop," Aoi nodded.
Yuki asked. "But what if a new person joins?"
"We have to lower compression ratio," Riku answered. "Can't be exclusive."
"Good insight," Aoi acknowledged. "If a group's compression ratio is too high, it excludes outsiders."
"The problem of expert groups."
Yuki became serious. "The Information Theory Club needs to be careful too."
"That's right," Aoi agreed. "Speak to new members with appropriate compression ratio."
Riku laughed. "Don't use 'that thing'."
The three smiled.
Conversation compression is a double-edged sword of efficiency and exclusivity. Balance is important.
Yuki summarized. "Today's conversation is probably compressed too."
"Certainly," Aoi answered. "But it gets through to us well enough."
"That's the power of shared context."
A comfortable silence visited the club room. Even without words, they understood each other. That too was a form of compression.