The Law of Inertia and the Principle Quidquid Movetur Ab Alio Movetur

Abstract

THE LAW OF INERTIA AND THE PRINCIPLE QUIDQUID MOVETUR AB ALIO MOVETUR HISTORY OF SCIENCE teaches us how difficult it is to discover the general laws of nature and the fictitious character of these laws. The fictitious character of the fundamental principles of physics is evident from the fact that we can point to two essentially different principles, each of which corresponds with experience to a large extent. Einstein calls philosophical prejudices the belief in the direct intuition of laws from nature through observation. The prejudice consists in the faith that facts by themselves can and should yield scientific knowledge without free conceptual constructions ... One does not easily become aware of the free choice of such concepts, which, through verification and language, appear to be immediately connected with the empirical materiaJ.l On the other hand, physicists should be aware of the importance played by philosophical ideas in the discovery of physical laws and physical theories. Every important physical theory presupposes a cluster of philosophical concepts regarding space, time, motion, causality, and so forth, which are a consequence of the philosophical world view of the pioneers of physics . All great physicists without exception were philosophers. One supposes Einstein, Bohr, Heisenberg and Dirac to be different kinds of thinkers from Galileo, Kepler and Newton. But this is wrong. These are all physicists: that is, natural philosophers seeking explanations of phenomena in ways more similar than the dichotomy "classical-modern" has led philosophers of science to imagine.2 1 A. Einstein, Essays in Science, (New York, 1934), p. 69. Cf. Albert Einstein: Philosopher-Scientist, ed. by Paul Schilpp (New York, 1951), p. 49. • N. R. Hanson, Patterns of Discovery (Cambridge, 1958), p. !l. 306 THE LAW OF INERTIA 307 The conceptual basis of De Broglie's doctoral thesis on matter seemed " philosophical " to his examiners. The dispute between Einstein, Bohr, Bohm, and De Broglie is regarded as merely philosophical by most physicists. Physicists, however, are philosophers of nature looking for the explanation of phenomena , as were Aristotle, Galileo, or Newton. A physicist is a philosopher of nature, and a philosopher of nature must know physics. It is the vision of the universe which counts, not the symbolism of its mathematical formulation. I. The Law of Inertia in Galileo and Newton A typical example of the fictitious character of physical laws and their philosophical implications is the Law of Inertia, called by Whitehead the first article of the creed of science, which reads: "Every body continues in its state of rest or of uniform motion in a straight line, unless it is compelled to change that state by forces inpressed upon it." 8 This law is not axiomatic in the sense of self-evident. It seemed plausible, however, to Galileo, Newton, and the majority of classical physicists. To prove this law, Galileo argued that a sphere rolling down a plane on one side of the room would roll across the floor and up an inclined plane on the opposite side. Moreover, ignoring friction, the sphere will ascend the second plane to just the height above the floor from which it had been released on th~ first inclined plane. Hence, a sphere in motion on an ideal frictionless floor would move along a straight line to infinity. "We may remark," Galileo says, " that any velocity once imparted to a moving body will be rightly maintained as long as the external causes of acceleration or retardation are removed, a condition which is found only on horizontal planes ..." 4 That 3 I. Newton, Philosophiae Naturalis Principia Mathematica (London, 1687), Law I. cf. A. N. Whitehead, Essays in Science and Philosophy (London, 1948), p. 171. • Galileo, Two New Sciences, IIIrd day, pp. 215-fH6, Cf. ibid., "Any velocity once received by a body is perpetually maintained as long as the external causes of acceleration or retardation are removed, a condition which is found only in horizontal planes." 308 ANTONIO MORENO this motion will be uniform ad infinitum is assumed to follow from Galileo's "thought experiment" by simply passing to the limit. Theoretically speaking, the Law of Inertia can be considered as a particular case of the Second Law of Motion, name- ~ ly, force is equal to...