An acquaintance of mine juggles several jobs and spends most of the year traveling.
When she leaves the country, she walks out of her apartment in Nishi-Shinjuku about two hours earlier than she needs to. Then she takes the Yamanote Line from Shinjuku Station—the outer loop, clockwise. Her flight leaves from Haneda, which means the sensible route would be the inner loop to Shinagawa and a transfer to the Keikyu Line, or a train toward Tokyo Station and the monorail from Hamamatsucho. She knows this. She takes the long way anyway.
Once she's on the outer loop, heading in the wrong direction, she settles in and watches the city go by. Hamamatsucho comes and goes. Shinagawa comes and goes. Eventually the train rolls back through Shinjuku, the station she boarded an hour ago. She stays on. Somewhere into her second lap, she finally gets off—at Hamamatsucho or Shinagawa—and connects to Haneda.
When I asked her about it, she smiled. "It's a slingshot," she said.
A gravitational slingshot—or gravity assist—is a technique in orbital mechanics. A spacecraft swings close to a planet and borrows energy from the planet's gravity and its motion through space, gaining speed relative to the solar system as a whole. Or losing it, depending on the approach. Either way, the planet does the work.
The efficiency is the point. A spacecraft that uses gravity assists needs less fuel. Less fuel means a lighter launch. Travel farther, carry less.
I wonder if that's what she's doing on the Yamanote Line—using Tokyo's gravity to get up to speed before she leaves it behind. She does travel light; her bags are always minimal. Maybe she rides the outer loop to take one last look at the city's center of mass, to feel it pull at her before she lets go.
Somewhere in that second lap, headed for the gate. That's the idea, at least.
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