“Jaunt’s a bunch of psychos,” this parallel version of me said, voice shaking with fear. “To blow up a whole airplane just to keep us quiet? They’re totally off their rockers!”
“Yes, they certainly are,” I—that is, the me here—replied, mockingly. “Our enemy is powerful. Thinking back on it, Alice was saying some disturbing stuff about being able to change the world and whatnot. And no, I don’t think Alice did it—but we can see that they’re putting these ideas into the heads of little kids like Alice. That’s what you call brainwashing, right? Man, I can’t forgive myself for overlooking that at the time.”
“Yes, I agree. But what we’re talking about right now—what’s important—is something else…”
“Yes,” I laughed. “Jaunt is certainly a powerful organization. They’d have to be to get a bomb on a plane. A junior high school girl hardly has a chance against something like that.”
“But,” “I” continued, “I’m not alone.”
“I have infinite ‘mes’ with me.”
“Infinite parallel worlds, infinite possibilities. Infinite versions of us.”
“Do you remember what Tenjou was saying before about the properties of light? What was it…Fermat’s theorem?”
“No, no, it was Fermat’s principle. A ray of light between two points, of all the possible routes, takes the route that allows it to travel in the least amount of time.”
It might sound strange, but light always takes the path to its destination that requires the least amount of time. If there’s nothing between the two points, it naturally travels in a straight line—because that’s the path that takes the least amount of time. But if there’s an obstacle in the middle, like water or air or gravity, it’s a different story. For example, light travels more slowly through water than it does through air. If it has to pass through water to go in a straight line, that will slow it down by a lot. Therefore, light chooses a bent path. It takes the route that takes the least amount of time, minimizing the distance it travels through water, without traveling an unnecessary distance through air either.
Think of water like a crowded street: Even if it’s the shortest distance, anyone would want to avoid trudging through a jam-packed group of people. You’d want to look for an uncrowded detour if you could. But if you took a big detour to avoid a jam, that could be even worse because you’d just waste time traveling more than you had to. Light is a master that finds the perfect balance between avoiding jams when feasible and avoiding excessive detours.
That’s what’s called Fermat’s principle.
The funny thing about this principle is that it looks as if light knows the destination it will reach ahead of time. It seems as if it picks the route that arrives in the shortest amount of time with complete awareness of not just the destination, but even what obstacles exist on the way, what mediums it will have to pass through, and what angle of incidence it needs, how it needs to bend. You see, there’s no way you could pick the route that arrives in the least amount of time unless you already knew all of the paths before you left and knew which of them were crowded. Yet light finds that route in an instant.
How does it do it?
Nanami said, “This is how quantum mechanics explains it. Light doesn’t choose the route that arrives in the least amount of time before it leaves. It travels every possible route at the same time. But all the rays that travel routes other than the one that arrives in the least amount of time interfere and cancel each other out. In the end, only the route that connects the two points in the least amount of time is left. That’s why it looks as if light always picks the route that arrives first. Light is also a quantum, with both wave and particle properties.”
So, light too interferes with its own possibilities or parallel worlds. It doesn’t know the way to the destination in advance. Its quanta simultaneously travel every path, and in the end only the correct answer is left, the route that connects the two points in the shortest time. Such are the properties of light, from the perspective of quantum mechanics.
“You see it, don’t you?” went my conversation over the phone.
“All I have to do is make reaching Alice my only objective.”
Right. I just had to become like a beam of light. I just had to think about how to reach Alice in the shortest possible time. Then every “me” would be searching for Alice in every single world. It didn’t matter how big or scary Jaunt was. I had countless possibilities, infinite parallel worlds on my side. And this cell phone of mine allowed “us” to interfere with each other.
“It’s not that difficult. Light doesn’t understand Fermat’s principle or Feynman path integrals, either. Light is just that: light. That’s enough for it to find the route that reaches the destination in the shortest time, so I don’t have to think hard about it either. I simply need to focus on my objective. That just has to be how I go. Then eventually one of the infinite ‘mes’ will arrive at the solution, and that’s all that will remain.”
“Just like how the I who didn’t get on the plane stayed around and the ‘me’ who died on it didn’t.”
“Exactly. Only the correct possibility remains uncanceled.”
Yes. I’ll become like light. I’ll use the phone that Yukari gave me. And for now, inevitably, I’ll reach Alice.
Yes—for now.
The best cure for sadness was rage. It was a harsh, bitter medicine, but it saved my heart from splitting wide open from tragedy. Harsh medicine can hurt you, but as always, I adapted to it right away.
I think at this point I’d already quit being Hatou Manabu.