Step Day was the day in 2015 when Willis Linsay uploaded the circuit diagram for the Stepper Box onto the Internet.
The Stepper Box caused the Long Earth to become a phenomenon known by all humans, and made stepping possible for everyone (rather than just natural steppers, like in the past).
On Step Day, when the diagram was first released, kids from all around the world started putting together Steppers and disappeared.
- ↑ The Long Earth - Chapter 2
- ↑ 2.0 2.1 The Long Earth - Chapter 3
- ↑ The Long Earth - Chapter 33