THE ROLE OF INTERPRETATIONS IN PHYSICS
A statement of fact or a scientific hypothesis restated in terms of a new metaphysical doctrine is a new interpretation. New interpretations are only too often unsatisfactory explanations of the original statements - for example, interpreting a motive as a sex motive, or survival as due to a high degree of fitness, or change of a person’s pattern of behavior is due to physical change in the brain.
But the logic of interpretations is made clearer, and so is their possible usefulness, when we take examples from physics.The handles of ajar stick to the jar. To repeat this in Newtonian terms, the particles of the jar are attracted (by some central forces, that is) to those of the handles. Is this restatement a circular or a satisfactory explanation? We do not know. How small are these particles? What is the magnitude of these forces? One may try an estimate on the basis of known facts - perhaps the force needed to tear the handles off. Or perhaps it is easier to measure the force of cohesion by observing a drop of water hanging on to a solid surface, where cohesion counteracts gravity. Or perhaps it is still easier to observe a drop of water in a tube, where the balance of cohesion and gravity is perfect, and where the weight of the drop and the area of the contact surface are more easily calculable. It is easy to develop the first step of Laplace’s theory of capillarity by thinking along this line: restate the connection between the inner diameter of the glass tube and the height of the water-column (or mercury surface) in it in Newtonian terms. As Newtonian forces are central, it would follow at once that the narrower the glass tube the higher the water column (and the lower the mercury level) in it. And the relative curvature of the fluid surfaces will be equally easily explicable. This is a particularly fortunate interpretation.
Another example: Newtonianism forces us to view light as either particles or waves in an elastic medium.
Each of these interpretations leads to obvious questions which may be given testable answers. Faraday’s metaphysics, to take another example, which views the universe as one field of forces, invites the view that light consists of vibrations of the lines of force in empty space. Faraday himself considered light to be waves of the magnetic field of force. For decades he tried to test this hypothesis and failed. And Faraday’s interpretation of the electric current as the collapse of an electric field is another example of his failure. Tyndall rightly declared that Faraday’s theory of the current was unsatisfactory. But he was too eager to reject it offhand (being a dogmatic Boscovitchian); by further specification Poynting soon rendered it highly satisfactory.Interpretations apply not only to facts but also to theories. Faraday accepted Coulomb’s Newtonian theory of electrostatic forces, but reinterpreted it in his field conception. His interpretation seemed unsatisfactory, and he was painfully aware of this. He succeeded in rendering it satisfactory by looking for curved lines of electric forces, which his interpretation of Coulomb’s theory, though not Coulomb’s theory itself, allowed for. He thus found that electric lines of force curve in the presence of dielectrices, i.e., materials like glass or sulphur. It is no accident that Coulomb denied the possibility of dielectricity: he was a Newtonian. Nor is it accidental, I think, that Cavendish failed to publish his own discovery of dielectricity: he wished to work on it further and reincorporate it within Newton’s metaphysics, and he died before accomplishing this formidable task. That this task could be performed with but a slight deviation from Newton’s program Faraday knew, and he outlined ways of doing it, without however being able to do so himself for want of mathematical technique. The technique had been provided by Poisson, and Faraday said as much, but he was too neurotic about mathematical symbols to write them down on paper.
Shortly afterwards Liouville was in a quandary because Poisson had, on his death-bed, asked him to make Poisson’s own work the topic of a prize essay, and Liouville felt understandably apprehensive in view of Faraday’s discovery which seemed to him not to fit Poisson’s Newtonianism too comfortably. Kelvin, who was a young lad then, related all this in a letter which he wrote to his father from Paris, and he added a description of how relieved Lionville was to hear that Kelvin could interpret Faraday’s discovery in an almost Newtonian fashion by using Poisson’s own method. This was Kelvin’s first published paper.But there was no escape from Faraday’s inspirations. Kelvin’s theory of the dielectric assumed gross matter to possess electrical properties; his theory was not Newtonian but Boscovitchian. It soon transpired that Bos- covitch’s program needed modification. Gauss and Weber tried, and the attempt continued until 1905. By then it was clear that the program had to be given up; it looked as if Faraday’s program had won out at last. Yet this program too was abandoned very soon after. It was deterministic and determinism had to be abandoned.
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