| "Illusion" is a misleading way to put it. We experience gravity as a force - we can measure it with devices designed to measure forces. It's not an illusion. However, the model of gravity as a force between massive objects does not capture certain aspects of gravity - it's an incomplete model. That doesn't actually mean that gravity is "really a geometric manifestation due to the curvature of space-time". Gravity appears to behave that way, but what do you mean by "really" in that sentence? What we can say with confidence is that the spacetime curvature model is a more precise and complete model of gravity than the mass/force model. Perhaps if we figure out how to unify quantum phenomena with gravitation, we'll find a different model for gravity in that context. Will you then say that gravity wasn't "really" spacetime curvature? That wouldn't make sense, because all that will have changed is that we would have another model for interpreting and understanding gravity. When people say gravity is an "illusion" or that forces are "fictitious", what they're really getting at is that these observed phenomena are not fundamental - that they're consequences of some underlying phenomena. But they're real consequences, not illusory or fictitious. (Of course "fictitious" is a technical term used in physics, but it doesn't mean "does not exist in reality" but rather means something more like "is not fundamental".) |