flat spacetime

例句：

1. 1. In this flat spacetime, the distance between two points is constant.
   在这个平坦的时空中，两点之间的距离是恒定的。
2. 2. The flat spacetime theory suggests that gravity is a force that acts over large distances.
   平坦的时空理论表明，重力是一种作用在远距离上的力。
3. 3. The flat spacetime model has been used to explain the behavior of black holes.
   平坦的时空模型被用来解释黑洞的行为。