Light passing through curved spacetime appears to travel more slowly relative to an external observer.

穿过弯曲的时空的光相对于外部观察者而言传播的速度更慢。

Or held in orbits by the invisible force of gravity? Or are they following helical paths which are actually straight lines in curved spacetime?

还是被无形的地心引力控制在轨道上？它们是沿着在弯曲时空中实际上是直线的螺旋路径移动吗？

This is the effect of the highly curved spacetime which  causes time dilation.

这是高度弯曲的时空导致时间膨胀的影响。

They  only look like they curve around because they are travelling through a curved spacetime.

它们看起来只是弯曲的，因为它们正在穿越弯曲的时空。

The more dense an object is the  more it curves spacetime, and the more curvature there is the stronger the force of gravity.

物体密度越大， 时空弯曲得越多，曲率越大， 引力越强。