Physics, generally, does not provide causal explanations only descriptions. This is very important for some aspects of GR, but 'moving through time' is a reasonable simplification for this explanation We get around this by defining some other term that time changes through. **My use of motion is not technically correct, sine motion is defined as how an object changes its location through time. Again with the analogy, if an airplane does not use its rudder and there are no crosswinds, it will fly in an autoparallel line. When speaking technically, we prefer to use the term 'autoparallel', which means a line that does not change its direction at any local point. *The idea of a straight line is a little weird to think about in a curved geometry. Everything is moving** through time, and the curvature of gravity turns that motion into the gravity that we observe Now you might be wondering 'doesn't this mean that non-moving objects should be unaffected by gravity?' Remember that it is the curvature of space- time. The curvature of spacetime does something similar. For example, look at a map of flight paths the Earth is curved, so a direct flight between two cities will appear to curve on a flat map. The simple handwavy explanation is that a curved geometry makes straight* lines appear curved when you use flat geometry. Unfortunately, it looks like it works, leading to its overuse, and subsequent confusion when people later think about it. Basically, the rubber sheet explanation of GR is a really bad analogy.
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