Where Stella went wrong was her assumption that she and Terra had equal claim to being inertial observers.

史黛拉出错是因为她的假设错了，即假设她和特拉都是惯性观测者。

To be an inertial observer, one has to maintain a constant speed and direction relative to the rest of the universe.

作为惯性观测者，必须相对于宇宙的其余部分保持恒定的速度和方向。