# Question on gravity and spacetime curvature [duplicate]

In General Theory of Relativity, it is explained that the fabric of reality i.e. spacetime bends around objects with mass, and that curvature causes other objects to come close to/ fall towards the original object. This creates Gravity. While I know that the space time bends in a 3D manner, but the rubber sheet and 2D bending explains it intuitively. My question is this: what causes the object to fall in the curvature of space time?

Consider an inclined surface with inclination 'x' and an object with mass m on the inclined. Then the object of pulled down by a force 'mg sin(x)' parallel to surface of incline. This the force pulling object down on incline is a component of the gravitational force on the object. Then what is the fundamental force of which a component causes an object to fall in space time curvature, similar to how gravitational force has a component which causes object to slide down on an incline???

• Does this answer your question? What makes matter travel along geodesics? Commented Aug 7, 2023 at 12:32
• – Sten
Commented Aug 7, 2023 at 12:34
• You might also ask yourself a similar question in the context of classical physics: What causes objects to continue to move by inertia? Or, what is it about forces that causes objects to change their motion? Like, when something is acted upon by gravity - what causes it to move, exactly (not this abstract "attraction", but what mechanism)? Or why can it be described by the Newton's law of gravitation? Or, even, why forces obey Newton's laws in the first place. There is no answer to the "why" question, we can just explain "how" with increasing amount of depth, until we can't. 1/2 Commented Aug 7, 2023 at 18:00
• "My question is this: what causes the object to fall in the curvature of space time?" - ultimately, we don't know. We just know that objects tend to follow geodesics, trajectories that correspond to straight lines in curved spacetime. It's just something we've observed to be true. Someone well versed in GR might be able to give you some explanation that's more in depth, but then you might ask, "Well, why is that the case?", and there would be no answer. Not until we have some deeper theory, some further advancement in physics. 2/2 Commented Aug 7, 2023 at 18:00
• Very relevant XKCD: explainxkcd.com/wiki/index.php/895:_Teaching_Physics Commented Aug 7, 2023 at 18:17