The work of George Smith has illuminated how Newton’s scientific method, and its use in constructing the theory of universal gravitation, introduced an entirely new sense of what it means for a theory to be supported by evidence. This new sense goes far beyond Newton’s well known dissatisfaction with hypothetico-deductive confirmation, and his preference for conclusions that are derived from empirical premises by means of mathematical laws of motion. It was a sense of empirical success that George was especially (...) well placed to identify and to understand, through his experience as an engineer specializing in failure analysis. For Newton, to understand how well his theory was supported by evidence, he had to anticipate, as far as possible, all the ways in which it might be wrong. This paper explores how Newton's empirical method shaped his thinking about space, time, and the relativity of motion. (shrink)

This book presents an introduction to Einstein's Theory of Relativity, which has become a necessary part of the theoretical equipment of every physicist. Even if we regard the Einstein theory of relativity merely as a convenient tool for the prediction of electromagnetic and optical phenomena, its importance to the physicist is very great, not only because its introduction greatly simplifies the deduction of many theorems which were already familiar in the older theories based on a stationary ether, but (...) also because it leads simply and directly to correct conclusions in the case of such experiments as those of Michelson and Morley, Trouton and Noble, and Kaufman and Bucherer, which can be made to agree with the idea of a stationary ether only by the introduction of complicated and ad hoc assumptions. (shrink)

Resumen En este trabajo evaluamos el impacto que la adopción de la relatividad del movimiento tiene en la metafísica de Leibniz. En particular argumentamos que el abandono de la comprensión absolutista del mismo anula su noción juvenil de sustancia corpórea. En primer lugar analizamos cómo entiende Leibniz las nociones de cuerpo y movimiento en el periodo juvenil y defendemos que la comprensión absolutista de este último constituye una piedra angular en su primera concepción de la sustancia corpórea. En segundo lugar (...) exponemos los argumentos leibnizianos a favor de la relatividad del movimiento durante el período parisino y mostramos su repercusión en el concepto juvenil de sustancia corpórea.In this paper we evaluate the impact of Leibniz's defense of relativity of motion on his metaphysics. We argue that the abandonment of the absolutist position makes void his first notion of corporeal substance. First, we analyze Leibniz's conception of body and movement in his youth and explain how the assumption of absolute motion during these years plays a role in his notion of corporeal substance. Second, we examine his arguments in favor of relativity of motion during the Parisian period and show the repercussion on his first conception of the corporeal substance. (shrink)

The problem of motion in general relativity is about how exactly the gravitational field equations, the Einstein equations, are related to the equations of motion of material bodies subject to gravitational fields. This article compares two approaches to derive the geodesic motion of matter from the field equations: the ‘T approach’ and the ‘vacuum approach’. The latter approach has been dismissed by philosophers of physics because it apparently represents material bodies by singularities. I argue that a (...) careful interpretation of the approach shows that it does not depend on introducing singularities at all and that it holds at least as much promise as the T approach. (shrink)

This paper examines the young Kant’s claim that all motion is relative, and argues that it is the core of a metaphysical dynamics of impact inspired by Leibniz and Wolff. I start with some background to Kant’s early dynamics, and show that he rejects Newton’s absolute space as a foundation for it. Then I reconstruct the exact meaning of Kant’s relativity, and the model of impact he wants it to support. I detail (in Section II and III) his (...) polemic engagement with Wolffian predecessors, and how he grounds collisions in a priori dynamics. I conclude that, for the young Kant, the philosophical problematic of Newton’s science takes a back seat to an agenda set by the Leibniz-Wolff tradition of rationalist dynamics. This results matters, because Kant’s views on motion survive well into the 1780s. In addition, his doctrine attests to the richness of early modern views of the relativity of motion. (shrink)

John Granville's first book is unique on several counts. First, it's not simply a history of science, but rather a history of our evolving unerstanding of motion. It's unique in the detailed explanations given to common scientific riddles-explanations aimed to help students avoid catastrophic collisions with these concepts in college. It's unique in that it resents the philosophies on which the major scientific paradigm shifts rest. It's unique in its presentation from Thomas Kuhn's point of view (i.e., his concept (...) of world view and paradigm shifts as presented in his classic work The Structure of Scientific Revolutions). The book begins with an informal discussion of Kuhn's notion of world view, and various concepts relevant to his thesis concerning the nature of scientific revolutions; but, the Discovery of Motion proper begins with ancient Egyptian and Greek preparations for Aristotle (here the dialectic of Parmenides and Plato are given special attention). A survey of Aristotle and his science of motion follows (i.e., his theory of nature and natural philosophy). Included in this part of the book are the works of such notables as Archimedes and Ptolemy. The Copernican revolution, including the works of Galileo, Kepler and Newton is, of course, presented from the viewpoint of Kuhn's paradigm shift. Four chapters concerning Newtonian motion are the highlight of the first half of the book. It is here Granville's original aim, of explaning puzzling scientific phenomena to young students, is realized-but now this material serves another purpose. These chapters not only clarify Newton's world view but expose phenomena that were virtually invisible to the peripatetics...and will eventually expose reasons for the ambivalence and frustration that accompany scientific revolutions. Granville then turns to philosophical developments that led to our modern view of the world. This part of the book covers the evolution of empiricism from Bacon to Hume (with Descartes' rationalism thrown in for contrast). Kant's epistemology concludes this philosophical survey, deliberately leading the plot back toward the classical viewpoint. Finally, developments of the nineteenth century that led to the so-called Second Scientific Revolution are considered. The final chapter is a unique presentation of Einstein's relativity theory, where the incompatibility of this theory with Newtonian physics, and the reason why relativity must take precedence, are discussed. Granville compares the opposition to the Copernican revolution with twentieth century opposition to the Einsteinian revolution. The book reveals that, after building detailed understanding of classical Newtonian phenomena, opposition to a shift of world view is an understandable human reaction. (shrink)

Leibniz’s and Whitehead’s analyses of motion are at the heart of their metaphysical schemes. These schemes are to be considered as two blueprints of a similar metaphysical intuition that emerged during two breakthrough eras, that is, the 17th century and the beginning of the 20th century, and retained the Aristotelian idea that existence requires an active principle. The two philosophers’ attempts to elucidate this idea in the context of their analyses of motion still interact with central, longstanding questions (...) in philosophy, in particular that concerning the ontological status of change. For both thinkers, the phenomenon of motion is an example par excellence, of the metaphysically fundamental principle of action that is required for change in the world. I focus on Leibniz’s and Whitehead’s similar understanding of the concept of transition that is inserted as an essential constitutive component of motion and ensures its status as something real.Keywords: Gottfried Leibniz; Alfred Whitehead; Motion; Change; Relativity; Transition. (shrink)

The author argues that Newton’s distinction between absolute and relative motion, i.e. the refusal to define motion in relation to sensible things, in “Scholium on time, space, place and motion” from _Mathematical Principles of Natural Philosophy_, stems in great part from his critical stance towards Descartes’s philosophy of nature. This is apparent from the comparison of “Scholium”, in which Descartes is not mentioned at all, with Newton’s criticism of him in his manuscript _De gravitatione_. The positive results (...) of Newton’s encounter with Descartes’s theory of motion is almost completely identical to those of the “Scholium”: the definition of motion must concern the whole body and not just its surface; instead of “mutual translation”, it must include the force that is the cause of the physical motion; the motion of the bodies is uniform and straightforward, which can only be achieved within absolute space. As far as the theory of motion is concerned, Newton’s philosophical challenge was always Descartes. (shrink)

The concept of forcefree motion is primitive, i.e., unexplained, in special relativity. The paper demonstrates a way to characterize it by “more primitive,” directly operationally interpreted notions. These are the worldlines of (more or less) pointlike, but non-quantum bodies and of light signals, clock parametrizations of the former kind of worldlines and the direction, in which an observer sees a light signal go out. Already at this general level one can define the “radar distance” and the “radar (initial) (...) velocity” of one body with respect to another, and can define in a reasonable manner that two bodies move in “opposite directions” with respect to an observer. These concepts are then used to formulate a certain criterion for path structures which can experimentally be tested without presupposing inertial frames, atomic clocks, etc. It is demonstrated that the path structure of free motion in gravity-free regions of space-time, i.e., in the domain of validity of special relativity, satisfies that criterion. (shrink)

We examine the process of the emission of light from an atom that is in a relative translational motion with respect to the medium at rest in which the electromagnetic excitations propagate. The effect of Lorentz contraction of the of electron orbits on the emitted frequency is incorporated in the Rydberg formula, as well as the emitter’s Doppler effect is acknowledged. The result is that the frequency of the emitted light is modified by a factor that is identical with (...) what is called the ‘relativistic Doppler effect’. The new emission formula is applied for reinterpretation of the Ives-Stilwell experiment and shown that within the second order of approximation with respect to the speeds of the atom and the ‘absolute speed’ (Earth’s speed relative to the medium), the absolute motion does not affect the interference. The expression for the modification of the frequency involves both a first and a second-order term with respect to the speed of the atoms in the cathode tube. The latter turns out to be quantitatively the same as if the time would have changed its rate in the frame moving with the atoms. Thus, a new interpretation of the results of this famous experiment is provided without stipulating time dilation. (shrink)

This paper and its predecessor () are about the question: 'Are the events in the entire universe encoded in and predictable from any of its parts?' To approach a positive answer in classical physics, the following result is proved and commented on: in Newton's theory of gravitation, the entire trajectory of a particle can be predicted given any segment of it, regardless of how the other particles are moving-provided that there is only a finite number of particles and that their (...) speeds remain bounded. (It is this condition, together with a set of parameters characterising the motion of the other particles, which enables us to estimate the effect of the other particles on the trajectory of the given particle.) The extension of this result to other theories, in particular to special relativity, is discussed. (shrink)

In illusory line motion, presentation of a cue is followed by presentation of a nearby stationary line, and the line is perceived to “unfold,” “expand,” or “extend” away from the cue. Effects of the allocation of attention regarding where the cue or the line would be presented were measured in three experiments, and ratings of relative velocity and relative strength of illusory motion were collected. Findings included (a) relative velocity and relative strength decreased with increases in SOA from (...) 50 to 450 ms, (b) relative velocity and relative strength were not influenced by whether illusory motion moved from one end of the line to the other or from both ends toward the middle of the line, (c) increased uncertainty regarding where the line would appear did not influence relative velocity or relative strength, and (d) valid pre-cues regarding the location of a cue resulted in faster relative velocity than did invalid pre-cues, but pre-cue validity did not influence relative strength. Implications of these findings for the relationship of such illusory motion and attention (e.g., divided attention, shifts in attended location) are considered. (shrink)

We derive, from the Einstein-Maxwell field equations, the Lorentz equations of motion with radiation reaction for a charged mass particle moving in a background gravitational and electromagnetic field by utilizing a line element for the background space-time in a coordinate system specially adapted to the world line of the particle. The particle is introduced via perturbations of the background space-time (and electromagnetic field) which are singular only on the source world line.

An operational approach to quantum mechanics has been developed in the past decades in our group in Brussels. A similar approach is taken in this work, making use of the extra operational depth offered by this approach, to show that the construction of spacetime is specific to each observer. What is usually referred to as the block universe then emerges by noting that parts of the past and future are also contained in the present, but without the limitations that a (...) four-dimensional block universe usually implies, of a reality in which change would be impossible. In our operational approach, reality remains dynamic, with free choice playing a central role in its conceptualization. We also show that, when operationally analyzed, the theory implies that objects move not only in space, but also and especially in time, and more generally in spacetime, with their rest mass being a measure of their kinetic time energy. We therefore claim that Einstein’s relativity revolution has not been fully realized, since most physicists are not ready to accept these consequences of the theory although the formula’s showing them, when operationally analyzed, are in every relativity textbook. In particular, when relativistic motion is revisited as a genuine four-dimensional motion, it becomes possible to reinterpret the parameter c associated with the coordinate speed of light, which becomes the magnitude of the four-velocity of all material entities. We observe that this four-dimensional motion in Minkowski space can also be better understood if placed in the broader perspective of quantum mechanics, provided that non-locality is interpreted as non-spatiality, thus indicating the existence of an underlying non-spatial reality, the nature of which could be conceptual, consistent with the conceptuality interpretation of quantum mechanics. This hypothesis is reinforced by noting that when observers, or experiencers, as they will be referred to in this article, are described by acknowledging their cognitive nature of entities moving in a semantic space, Minkowski metric emerges in a natural way. (shrink)

The notions of ``motion'' and ``conserved quantities'', if applied to extended objects, are already quite non-trivial in Special Relativity. This contribution is meant to remind us on all the relevant mathematical structures and constructions that underlie these concepts, which we will review in some detail. Next to the prerequisites from Special Relativity, like Minkowski space and its automorphism group, this will include the notion of a body in Minkowski space, the momentum map, a characterisation of the habitat (...) of globally conserved quantities associated with Poincare symmetry -- so called Poincare charges --, the frame-dependent decomposition of global angular momentum into Spin and an orbital part, and, last not least, the likewise frame-dependent notion of centre of mass together with a geometric description of the Moeller Radius, of which we also list some typical values. (shrink)

Languages differ systematically in how to encode a motion event. English characteristically expresses manner in verb root and path in verb particle; in Chinese, varied aspects of motion, such as manner, path and cause, can be simultaneously encoded in a verb compound. This study investigates whether typological differences, as such, influence how first and second language learners conceptualise motion events, as suggested by behavioural evidences. Specifically, the performance of Chinese learners of English, at three proficiencies, was compared (...) to that of two groups of monolingual speakers in a triads matching task. The first set of analyses regarding categorisation preferences indicates that participants across groups preferred the path-matched (rather than manner-matched) screens. However, the second set of analyses regarding reaction time suggests, firstly, that English monolingual speakers reacted significantly more quickly in selecting the manner-matched scenes compared with monolingual speakers of Chinese, who tended to use an approximately equal amount of time in making manner- and path-matched decisions, a finding that can arguably be mapped onto the typological difference between the two languages. Secondly, the pattern of response latency in low-level L2 learners looked more like that of monolingual speakers of Chinese. Only at intermediate and advanced levels of acquisition did the behavioural pattern of L2 learners become target-like, thus suggesting language-specific constraints from the L1 at an early stage of acquisition. Overall, our results suggest that motion event cognition may be linked to, among other things, the linguistic structure of motion description in particular languages. (shrink)

This richly detailed biography captures both the personal life and the scientific career of Isaac Newton, presenting a fully rounded picture of Newton the man, the scientist, the philosopher, the theologian, and the public figure. Professor Westall treats all aspects of Newton's career, but his account centers on a full description of Newton's achievements in science. Thus the core of the work describes the development of the calculus, the experimentation that altered the direction of the science of optics, and especially (...) the investigations in celestial dynamics that led to the law of universal gravitation. (shrink)

The notions of conservation and relativity lie at the heart of classical mechanics, and were critical to its early development. However, in Newton’s theory of mechanics, these symmetry principles were eclipsed by domain-specific laws. In view of the importance of symmetry principles in elucidating the structure of physical theories, it is natural to ask to what extent conservation and relativity determine the structure of mechanics. In this paper, we address this question by deriving classical mechanics—both nonrelativistic and relativistic—using (...) relativity and conservation as the primary guiding principles. The derivation proceeds in three distinct steps. First, conservation and relativity are used to derive the asymptotically conserved quantities of motion. Second, in order that energy and momentum be continuously conserved, the mechanical system is embedded in a larger energetic framework containing a massless component that is capable of bearing energy (as well as momentum in the relativistic case). Imposition of conservation and relativity then results, in the nonrelativistic case, in the conservation of mass and in the frame-invariance of massless energy; and, in the relativistic case, in the rules for transforming massless energy and momentum between frames. Third, a force framework for handling continuously interacting particles is established, wherein Newton’s second law is derived on the basis of relativity and a staccato model of motion-change. Finally, in light of the derivation, we elucidate the structure of mechanics by classifying the principles and assumptions that have been employed according to their explanatory role, distinguishing between symmetry principles and other types of principles (such as compositional principles) that are needed to build up the theoretical edifice. (shrink)

The problem of energy and its localization in general relativity is critically re-examined. The Tolman energy integral for the Eddington spinning rod is analyzed in detail and evaluated apart from a single term. It is shown that a higher order iteration is required to find its value. Details of techniques to solve mathematically challenging problems of motion with powerful computing resources are provided. The next phase of following a system from static to dynamic to final quasi-static state is (...) described. (shrink)

ArgumentWhen Copernicus pointed out that the apparent movement of the sun was in fact the effect of the rotation of the earth, he explained his view by referring to a passage in Virgil's Aeneid. Thus he established the link between science and literature. This topic recurred frequently in both science and literature whenever the question of the relativity of motion arose. In this article, I will focus above all on two authors who took up this question: Ernst Mach (...) and Hugo von Hofmannsthal. Moreover I will try to show the different roles of scientific and literary prose in the works of Mach and in Hofmannsthal's Das Glück am Weg. (shrink)

The General Theory of Relativity (GR) and the Dynamic Universe (DU) are evaluated in how they explain frequencies of atomic clocks. DU and GR predict the frequencies with equal accuracy, but their explanations, the postulates they apply in the explanations and the word-views that come along with them are entirely different. The central argument is that if unified and under- standable physics is appreciated, then DU deserves to be taken as a viable alternative to GR. In GR different frequencies (...) of identical atomic clocks are explained by letting rates of the flow of time in their frames of reference vary as functions of the clocks’ states of motion and gravitation. The GR- based world-view is nonunderstandable because GR violates absolute simultaneity, and disunified because quantum mechanics is built on different postulates than GR. In DU different frequencies of identical atomic clocks are explained by letting their frequencies vary as functions of their states of motion and gravitation. As DU commits to absolute simultaneity and as the postulates of DU suffice as the ontological ground of quantum mechanics at least partially, DU provides an under- standable and unified scientific world-view. -/- Résumé: La théorie de la relativité générale (RG) et de l’univers dynamique (UD) sont évalués sur la fac ̧on dont ils expliquent les fréquences des horloges atomiques. La RG et l’UD prédisent les fréquences avec une précision égale, mais leurs explications, les postulats qu’ils appliquent aux explications et les visions du monde qui les accompagnent sont entie`rement différents. L’argument central est que si l’on reconnaˆıt la physique unifiée et compréhensible, alors l’UD mérite d’ être considéré comme une alternative viable à la RG. En RG, différentes fréquences d’horloges atomiques identiques sont expliquées en faisant varier les vitesses de l’écoulement du temps dans leurs cadres de référence en fonction des états de mouvement et de la gravitation des horloges. La vue du monde basée sur la RG est incompréhensible parce que la RG viole la simultanéité absolue, et est désunifiée parce que la mécanique quantique est construite sur des postulats différents de ceux de la RG. Dans l’UD, différentes fréquences d’horloges atomiques identiques sont expliquées en laissant leurs fréquences varier en fonction de leurs états de mouvement et de gravitation. Comme l’UD s’engage à la simultanéité absolue et que les postulats de l’UD suffisent, au moins en partie, comme fondements ontologiques de la mécanique quantique, l’UD fournit une vision du monde scientifique compréhensible et unifiée. (shrink)

I argue that the Aristotelian definition of motion,“the act of what exists potentially insofar as it exists potentially,” and the mover causality principle,“whatever is moved is moved by another,” are compatible with Newton’s First Law of Motion, which treats inertialmotion as a state equivalent to rest and which requires no sustaining mover for such motion. Both traditions treat motion as such as requiring an initial, generating mover but not necessarily a sustaining motor. Through examining examples of (...) motion as treated by Newtonian physics, and through arguing that potential energy is Aristotelian potentiality, I argue that the First Law is understandable according to the Aristotelian definition as an incomplete act with a twofold ordination of the same potentiality. I then propose that, through the notion of spacetime, Special and General Relativity instantiate motion as a unity of differentiated prior and posterior parts that do not coexist in reality. (shrink)

This paper shows how key aspects of Aristotle’s core concepts of matter and motion, some of which have recently been shown to help make sense of quantum mechanical indeterminacy, align with some important results of the energy-momentum relationship of special relativity. In this conception, mobility and indeterminacy are inherently linked to each other and to materiality. Applying these ideas to massless particles, which relativity tells us move at the maximal cosmic speed, allows us to draw the conclusion (...) that they must be the most basic physical bodies, that is, mobile substances. The most familiar massless particle, the photon, constitutes light. Furthermore, because the photon composes luminous matter but cannot be decomposed into anything else more basic, it fulfills the definition of element. (shrink)

We consider the motion of small bodies in general relativity. The key result captures a sense in which such bodies follow timelike geodesics. This result clarifies the relationship between approaches that model such bodies as distributions supported on a curve, and those that employ smooth fields supported in small neighborhoods of a curve. This result also applies to "bodies" constructed from wave packets of Maxwell or Klein-Gordon fields. There follows a simple and precise formulation of the optical limit (...) for Maxwell fields. (shrink)

Modern philosophy of physics debates whether motion is absolute or relative. The debate began in the 1600s, so it deserves a close look here. Primarily, it was a controversy in metaphysics, but it had epistemic aspects too. I begin with the former, and then touch upon the latter at the end.

I examine the reasons Aristotle presents in Physics VIII 8 for denying a crucial assumption of Zeno’s dichotomy paradox: that every motion is composed of sub-motions. Aristotle claims that a unified motion is divisible into motions only in potentiality (δυνάμει). If it were actually divided at some point, the mobile would need to have arrived at and then have departed from this point, and that would require some interval of rest. Commentators have generally found Aristotle’s reasoning unconvincing. Against (...) David Bostock and Richard Sorabji, inter alia, I argue that Aristotle offers a plausible and internally consistent response to Zeno. I defend Aristotle’s reasoning by using his discussion of what to say about the mobile at boundary instants, transitions between change and rest. There Aristotle articulates what I call the Changes are Open, Rests are Closed Rule: what is true of something at a boundary instant is what is true of it over the time of its rest. By contrast, predications true of something over its period of change are not true of the thing at either of the boundary instants of that change. I argue that this rule issues from Aristotle’s general understanding of change, as laid out in Phys. III. It also fits well with Phys. VI, where Aristotle maintains that there is a first boundary instant included in the time of rest, but not a “first in which the mobile began to change.” I then show how this rule underlies Aristotle’s argument that a continuous motion cannot be composed of actual sub-motions. Aristotle distinguishes potential middles, points passed through en route to a terminus, from actual middles. The Changes are Open, Rests are Closed Rule only applies to actual middles, because only they are boundaries of change that the mobile must arrive at and then depart from. On my reading, Aristotle argues that the instant of arrival, the first instant at which the mobile has come to be at the actual middle, cannot belong to the time of the subsequent motion. If it did, the mobile would already be moving towards the next terminus and thus, per Phys. VI 6, would have already left. But it cannot have moved away from the midpoint at the very same moment it has arrived there. This means that the instant of arrival must be separated from the time of departure by an interval of rest. I show how Aristotle’s reasoning applies generally to rule out any continuous reflexive motion or continuous complex rectilinear motion. On my interpretation, however, the argument does not apply to every change of direction. When, as in the case of projectile motion, multiple movers and their relative powers explain why the mobile changes directions, distinct sub-motions are not involved. Aristotle holds that such motions cannot be continuous, not because they involve intervals of rest, but because they involve multiple causes of motion. My interpretation of the Changes are Open, Rests are Closed Rule allows us to make better sense of Aristotle’s argument than any previous interpretation. (shrink)

In this article, we explore whether cross-linguistic differences in grammatical aspect encoding may give rise to differences in memory and cognition. We compared native speakers of two languages that encode aspect differently (English and Swedish) in four tasks that examined verbal descriptions of stimuli, online triads matching, and memory-based triads matching with and without verbal interference. Results showed between-group differences in verbal descriptions and in memory-based triads matching. However, no differences were found in online triads matching and in memory-based triads (...) matching with verbal interference. These findings need to be interpreted in the context of the overall pattern of performance, which indicated that both groups based their similarity judgments on common perceptual characteristics of motion events. These results show for the first time a cross-linguistic difference in memory as a function of differences in grammatical aspect encoding, but they also contribute to the emerging view that language fine tunes rather than shapes perceptual processes that are likely to be universal and unchanging. (shrink)

A theorem due to Bob Geroch and Pong Soo Jang [“Motion of a Body in General Relativity.” Journal of Mathematical Physics 16, ] provides the sense in which the geodesic principle has the status of a theorem in General Relativity. Here we show that a similar theorem holds in the context of geometrized Newtonian gravitation. It follows that in Newtonian gravitation, as in GR, inertial motion can be derived from other central principles of the theory.

Lanczos, C. Einstein's path from special to general relativity.--Balazs, N. L. The acceptability of physical theories: Poincaré versus Einstein.--Ellis, G. F. R. Global and non-global problems in cosmology, by G. F. R. Ellis and D. W. Sciama.--Ehlers, J. The geometry of free fall and light propagation, by J. Ehlers, F. A. E. Pirani and A. Schild.--Trautman, A. Invariance of Lagrangian systems.--Penrose, R. The geometry of impulsive gravitational waves.--Exact solutions of the Einstein-Maxwell equations for an accelerated charge.--Taub, A. H. Plane-symmetric (...) similarity solutions for self-gravitating fluids.--Robinson, I. Equations of motion in the linear approximation, by I. Robinson and J. R. Robinson.--Florides, P. W. Rotating bodies in general relativity.--Chandrasekhar, S. A limiting case of relativistic equilibrium.--Israel, W. The relativistic Boltzmann equation.--Thompson, W. B. The self-consistent test-particle approach to relativistic kinetic theory. (shrink)

One of the issues dividing "absolutists" and "relationists" is the question whether all motion is relative motion or, in the words of Earman, spacetime has "structures that support absolute quantities of motion." This paper argues that, despite the enormous literature bearing on the topic, it is problematic to formulate a general criterion for when a quantity counts as absolute in contrast to merely relative in a way that is not hopelessly parasitic on other, presumably distinct, senses of (...) "absolute." Furthermore, I suggest that the vicissitudes of the evolution of the concept of absolute motion have contributed to this difficulty. (shrink)

A fundamental and familiar feature of Aristotle’s natural philosophy is his use of the concept of physis as an explanatory principle of the development and growth of certain kinds of things. Natural things are those that possess within them an original principle of continuous movement towards some completion. Nature is thus said to belong among the causes which are for the sake of something or are purposeful. The concept is crucial, Aristotle argues, if one is to be able to explain (...) the motion and phenomena that constitute life and development in the world. Lacking this concept, as the earlier philosophers did, natural science is seriously incomplete and inadequate. (shrink)

I begin by reviewing some recent work on the status of the geodesic principle in general relativity and the geometrized formulation of Newtonian gravitation. I then turn to the question of whether either of these theories might be said to ``explain'' inertial motion. I argue that there is a sense in which both theories may be understood to explain inertial motion, but that the sense of ``explain'' is rather different from what one might have expected. This sense (...) of explanation is connected with a view of theories---I call it the ``puzzleball view''---on which the foundations of a physical theory are best understood as a network of mutually interdependent principles and assumptions. (shrink)

We study the acceleration and collisions of rigid bodies in special relativity. After a brief historical review, we give a physical definition of the term ‘rigid body’ in relativistic straight line motion. We show that the definition of ‘rigid body’ in relativity differs from the usual classical definition, so there is no difficulty in dealing with rigid bodies in relativistic motion. We then describe The motion of a rigid body undergoing constant acceleration to a given (...) velocity.The acceleration of a rigid body due to an applied impulse.Collisions between rigid bodies. (shrink)

Where should we begin our story? Many books start with Newton, but Newton was responding to both Galileo1 and especially (for our purposes) Descartes. But Galileo and Descartes themselves were writing in the context of late Aristotelianism, and so were trained in and critical of that rich school of thought, so if we want to fully understand their work we would need to understand scholastic views on space and motion (see Grant, 1974, Murdoch and Sylla, 1978 and Ariew and (...) Gabbey, 1998). But late scholasticism itself is the result of a long history tracing from Plato and Aristotle through Jewish, Arabic, Islamic and European thought. And of course Plato and Aristotle are explicitly reacting to their predecessors and contemporaries. In other words, we could start the story as early in recorded thought as we like. (shrink)