Apples Falling, Buckets Rolling, and Why Inertia Keeps Trolling: Inertial Motion is Not Natural Motion
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arXiv
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| Format: | Preprint |
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2025
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| author | Bamonti, Nicola |
| author_facet | Bamonti, Nicola |
| contents | Inertia has long been treated as the paradigm of natural motion. This paper challenges this identification through the lens of General Relativity. Drawing on Norton (2012)'s distinction between idealisation and approximation and analysing key results from Tamir (2012) on the theorems of Geroch-Jang, Ehlers-Geroch, Einstein-Grommer, and Geroch-Traschen, I argue that geodesic motion -- commonly treated as the relativistic expression of inertia -- fails to qualify as either. Rather, geodesic motion is best understood as a useful construct -- a formal artefact of the theory's geometric structure, without real or fictitious instantiation, and excluded by the dynamical structure of General Relativity. In place of inertial motion, I develop a layered account of natural motion, which is not encoded in a single "master equation of motion." Extended, structured, and backreacting bodies require successively refined dynamical formalisms that systematically depart from geodesic motion. This pluralist framework displaces geodesic motion as the privileged expression of pure gravitational motion, replacing it with a dynamically grounded hierarchy of approximations fully consistent with the Einstein field equations. Inertial motion thus emerges not as the universal default of motion under gravity alone, but as a formal construct that stands apart from the pluralistic framework in which natural motion is genuinely realised. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2504_14734 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Apples Falling, Buckets Rolling, and Why Inertia Keeps Trolling: Inertial Motion is Not Natural Motion Bamonti, Nicola History and Philosophy of Physics General Relativity and Quantum Cosmology Inertia has long been treated as the paradigm of natural motion. This paper challenges this identification through the lens of General Relativity. Drawing on Norton (2012)'s distinction between idealisation and approximation and analysing key results from Tamir (2012) on the theorems of Geroch-Jang, Ehlers-Geroch, Einstein-Grommer, and Geroch-Traschen, I argue that geodesic motion -- commonly treated as the relativistic expression of inertia -- fails to qualify as either. Rather, geodesic motion is best understood as a useful construct -- a formal artefact of the theory's geometric structure, without real or fictitious instantiation, and excluded by the dynamical structure of General Relativity. In place of inertial motion, I develop a layered account of natural motion, which is not encoded in a single "master equation of motion." Extended, structured, and backreacting bodies require successively refined dynamical formalisms that systematically depart from geodesic motion. This pluralist framework displaces geodesic motion as the privileged expression of pure gravitational motion, replacing it with a dynamically grounded hierarchy of approximations fully consistent with the Einstein field equations. Inertial motion thus emerges not as the universal default of motion under gravity alone, but as a formal construct that stands apart from the pluralistic framework in which natural motion is genuinely realised. |
| title | Apples Falling, Buckets Rolling, and Why Inertia Keeps Trolling: Inertial Motion is Not Natural Motion |
| topic | History and Philosophy of Physics General Relativity and Quantum Cosmology |
| url | https://arxiv.org/abs/2504.14734 |