"What is a world line?"
Rasul took Mia and Mier to walk on the ruined streets and explained things to the two little girls.
“The world line is the world under probability distribution.”
“When you toss a coin, the probability of heads and tails being close to 50 percent.”
"But when the coin lands, there is only one outcome: either heads or tails."
Rasul flicked a coin with his fingers and then covered it on the back of his hand: "Guess which side is up?"
"I guess heads." said Mi'er.
"Then I'll guess the opposite," Mia said.
Rasul removed his hand from covering the coin.
Face up.
"What is the probability of the front side facing up at this time?" Rasul asked Mi'er.
"What's the probability at this time?" Mi'er asked in confusion, "Isn't it already confirmed? 100%?"
"That's right." Rasul said, "Why did the probability of heads facing up change from 50% at the beginning to 100% now?"
He asked himself and answered: "Because in the process of tossing the coin, your observation caused the world line you were in to collapse."
Mier seemed to be thinking about something, while Mia looked confused.
"On the long axis of time, the world line undergoes two changes at every moment: one is collapse, and the other is divergence." Rasul continued to move forward and explained, "Before you toss the coin, the world line diverges from this point and splits into two. The future line on the left is facing up, and the future line on the right is facing up."
"When the coin is tossed, your world line begins to collapse, with an equal chance of collapsing to the left or right, 50%. After the collapse is complete, the coin turns heads up, and your world line collapses to the future line on the left along with your observation."
"Then the question is, does the future line on the right, that is, the parallel world where the coin is 'tails up', exist for you?"
"According to what you said, it should exist." Mi'er replied, "From the moment you tossed the coin, the world line collapsed to the left, but the future line on the right still exists, but we can't observe it because of the collapse."
"Yes, you really understand what I mean." Rasul looked at her approvingly and glanced at Mia, who forced herself to remain calm and acted as if to say, "I understand too."
Rasul sighed inwardly.
"In this world, we are faced with probability all the time." Rasul continued, "When you wake up in the morning, should you brush your teeth first or eat breakfast first? After defeating a robber who tried to rob you, should you kill him or let him go? When you meet your beloved, should you confess your love or continue to have a crush on him?"
"Will it rain tomorrow? Will someone passing by suddenly have a myocardial infarction? Will the lottery ticket I bought last month win the prize?"
"Each probabilistic event represents a possibility in the future. Infinite probabilistic events are arranged and combined into infinite possibilities, which also radiate infinite future lines. When a probabilistic event throws its 'coin', the world line collapses into one of the future lines. This future line becomes the world line we observe, and continues to radiate infinite future lines forward."
"Wait." Mi'er suddenly said, "I remember Nora once said that all probabilities are actually pseudo-probabilities."