É um nome fácil para a ideia de que o universo exterior está se movendo muito mais rápido e as coisas pareceriam estar girando no céu se fossem visíveis.
Do livro:
"Spin" was a dumb but inevitable name for what had been done to the Earth. That is, it was bad physics - nothing was actually spinning any harder or faster than it used to - but it was an apt metaphor. In reality the Earth was more static than it had ever been. But did it feel like it was spinning out of control? In every important sense, yes.