Abstract
Chapter 1 offered a reading of the law of momentum conservation, which takes it to consist of structural assumptions about physical systems. Structural assumptions include a Criterion of Isolation and a Rule of Composition. One benefit of thinking of conservation laws as structural assumptions is that it makes clear the epistemic role of conservation laws. The Criterion of Isolation appears to be central to the scientific practice, since in order to attribute certain properties to parts of a system, physicists need a criterion for isolating the composite system from the environment. If a system is not approximately isolated, one cannot investigate the system, either theoretically or experimentally. Without a criterion for isolating the system, it is not possible to discern the causal processes that flow from one part of the system to another, and dissociate them from causal processes that arises from external factors.
This is a preview of subscription content, log in via an institution to check access.
Access this chapter
Tax calculation will be finalised at checkout
Purchases are for personal use only
Notes
- 1.
I should qualify these remarks and say that the initial investigation into causal processes requires a Criterion of Isolation. One can also apply the Criterion of Isolation in one dimension (for example, horizontally to the force of gravitation on the surface of the earth), or isolate a system only to a good approximation. Once, for example, a certain force is discovered, one can assume it exists without applying the Criterion of Isolation.
- 2.
Thus Primitive Motion Relationalism has conceptual ties to possibilist relationalism – see Manders (1982), Mundy (1986) and Teller (1991). Someone may worry that the analogy between spacetime theories and architectural plans is vitiated by the similarity between architectural plans and the buildings they describe. Architectural plans are often drawn on paper and are simply scaled spatial representations of the buildings themselves. This would seemingly undermine the purpose of the analogy, which is to argue that spacetime theories do not describe anything real. Drawings of buildings may not describe an existing building, but are themselves actualized spatial structures. However, this objection is easily rebutted if we think of computer programs that encode architectural plans. The printouts or screen simulations are not essential components of the plans, but are mere aids for humans in understanding the plans.
- 3.
The account here sheds new light on recent debates about the nature of motion. In recent discussions (see Tooley, 1988; Jackson and Pargetter, 1988; Arntzenius, 2000; Carroll, 2002; Lange, 2005), some have argued that instantaneous velocities cannot be defined as neighborhood properties or the derivative of a trajectory. Our normal scientific practice is based on the intuition that instantaneous motions are states of physical systems. The notion of a state of motion is required to explain the dynamic evolution of physical systems. For example, the Law of Inertia asserts that the state of motion of a body will remain unchanged if no external forces are impressed on the body. Thus, it is not enough to define motion as the limit on a series of ratios, since that limit is not a genuine property of the body which exists at a particular instant. We need instantaneous motions as properties that explain the dynamics of a physical interaction. But if we take instantaneous motions to be primitive states of a physical system, it is not clear what the relation is between primitive instantaneous motion and the derivative of the trajectory, which seems to be providing the definition of instantaneous motion. Our account alleviates this tension since it is assumed here that the derivative of the trajectory can only be defined relative to the Paradigm Uniform Motion, which is a paradigm for instantaneous primitive motions.
- 4.
Throughout the account the reader should keep in mind what is meant by the existential operators. Underlying the geometry are PUMs, which describe possible uniform motions. When the existential quantifier describes PUMs (in conjunction with Greek letters \(\alpha, \beta, \ldots\)) it is describing the existence of a possible uniform motion. The assumption is of a fixed domain interpretation of modality; all statements of predicate logic are referring to possible states of affairs.
- 5.
The extension of the approach here to curved spacetime will complicate matters, since it will require more than one coincidence point between PUMs in the case of spherical curvature. But the uniqueness of the coincidence relation is still true locally in curved spacetimes. The problem of how to define a neighborhood of a coincidence relation without relying on distance relations between points will be left for future work.
- 6.
In practice when calibrating clocks physicists often rely on objects that actualize, with good approximation, inertial motion. For example, the earth’s rotation around its axis is governed by the conservation of angular momentum to a good approximation. The sun and the earth orbiting the sun provide another good approximation. While these motions do not actualize a linear progression of a PUM, they do resemble PUMs between one instant and the next.
References
Arntzenius, F. 2000. “Are There Really Instantaneous Velocities?” Monist 83(2):187–208.
Brown, H. R. 2005. Physical Relativity: Space-time Structure from a Dynamical Perspective. Oxford: Oxford University Press.
Carroll, J. W. 2002. “Instantaneous Motion.” Philosophical Studies: An International Journal for Philosophy in the Analytic Tradition 110(1):49–67.
Jackson, F., and R. Pargetter. 1988. “A Question About Rest and Motion.” Philosophical Studies: An International Journal for Philosophy in the Analytic Tradition 53(1):141–46.
Lange, M. 2005. “Can Instantaneous Velocity Fulfill Its Causal Role?” The Philosophical Review 114(4):433–68.
Manders, K. L. 1982. “On the Space-time Ontology of Physical Theories.” Philosophy of Science 49(4):575–90.
Mundy, B. 1986. “Optical Axiomatization of Minkowski Spacetime Geometry.” Philosophy of Science 53(1):1–30.
Teller, P. 1991. “Substance, Relations and Arguments About the Nature of Space-time.” Philosophical Review 100(3):363–97.
Tooley, M. 1988. “In Defense of the Existence of States of Motion.” Philosophical Topics 16: 225–54.
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
Copyright information
© 2012 Springer Science+Business Media B.V.
About this chapter
Cite this chapter
Belkind, O. (2012). Primitive Motion Relationalism. In: Physical Systems. Boston Studies in the Philosophy of Science, vol 264. Springer, Dordrecht. https://doi.org/10.1007/978-94-007-2373-3_3
Download citation
DOI: https://doi.org/10.1007/978-94-007-2373-3_3
Published:
Publisher Name: Springer, Dordrecht
Print ISBN: 978-94-007-2372-6
Online ISBN: 978-94-007-2373-3
eBook Packages: Humanities, Social Sciences and LawPhilosophy and Religion (R0)