Universal Bias
Mystery of gravitation
All objects attract one another.
Early in the seventeenth century Rene Descartes proposed a mechanistic approach to physics, asserting that all causal influence is transmitted by direct contact between material entities. Like Aristotle, he rejected the idea of vacuum, believing that there can be no space (extension) without substance. In accord with his philosophy, Descartes denied the intelligibility of weight as a primitive quality of matter, and argued that material bodies are impelled toward the Earth by the impulse of particles of a "second species of matter" continually arriving at the Earth from all directions. Galileo, in his Dialogue Concerning Two New Sciences (1638), chose not to commit himself to any particular cause of gravity, indicating that he thought such speculations were premature at the present state of science. He wrote The present does not seem to be the proper time to investigate the cause of the acceleration of natural motion [i.e., gravity], concerning which various opinions have been expressed by various philosophers, some explaining it by attraction to the center, others to repulsion between the very small parts of the body, while still others attribute it to a certain stress in the surrounding medium which closes in behind the falling body and drives it from one of its positions to another. The first of these opinions is essentially the assertion of innate attraction and the third is a variation of Aristotle's proposal, which attribute the motive force of object in natural motion to a propagating interaction with a posited medium. (Aristotle's model has sometimes been ridiculed as being akin to a perpetual motion machine, but it is in essence just a crude description of a propagating wave.) The second opinion mentioned by Galileo is much less clear, but it seems to be alluding to an explanation of gravitation attraction based on repulsion and involving the very small parts of the body. Unfortunately Galileo didn't elaborate on this brief allusion, nor did he cite the philosophers who held that opinion, apparently because he considered these "opinions" to be common knowledge. But his comment suggests that people had speculated about the possibility of attributing the effects of gravity to repulsion acting on the microscopic parts of bodies. It's possible that he had in mind the bombardment of Descartes' "second species of matter". In the second half of the century, Isaac Newton deduced from a combination of terrestrial and celestial phenomena that every two particles of matter are compelled toward each other with a force directly proportional to their masses and inversely as the square of the distance between them. This "universal gravitation" provided a unified account of a wide range of phenomena that had previously seemed inexplicable and unrelated, but it was apparently contrary to the mechanistic precepts of Descartes, because it implied that widely separated bodies exert forces on each other directly, without explicit reference to any intervening substance. In private correspondence, Newton disavowed the notion of direct action at a distance, but at the same time he allowed for the possibility that the means by which the action of gravity is transmitted may not be material in which case the Cartesians would still regard it as unintelligible action at a distance. Acknowledging the success and utility of Newton's concept of universal gravitation, many continental scientists - such as Huygens, Leibniz, and the Bernoullis - sought some way of reconciling it with the mechanical philosophy of Descartes. In other words, they sought an explanation of universal gravitation in terms of direct contact between material entities.
For all latest news, follow The Daily Star's Google News channel.
Comments