isaac newton encounters objections -- 3/27/15

Today's selection -- from To Explain the World by Steven Weinberg. In Isaac Newton's three volume book Principia (or Philosophiæ Naturalis Principia Mathematica), published in 1687, 1713, and 1726, he set out his three laws of motion. It is regarded by many as the most important scientific book ever written. But when he wrote it, he had not worked out some of the mathematical proof, and many of the computations he did make had errors -- due especially to the measurement limitations of that era. And when he published it, he encountered significant objections to his theories:

"Book III of Principia presents calculations of things already measured, and new predictions of things not yet measured, but even in the final third edition of Principia Newton could point to no predictions that had been verified in the 40 years since the first edition. ...

"The Principia established the laws of motion and the principle of universal gravitation, but that understates its importance. Newton had given to the future a model of what a physical theory can be: a set of simple mathematical principles that precisely govern a vast range of different phenomena. Though Newton knew very well that gravitation was not the only physical force, as far as it went his theory was universal -- every particle in the universe attracts every other particle with a force proportional to the product of their masses and inversely proportional to the square of their separation. The Principia not only deduced Kepler's rules of planetary motion as an exact solution of a simplified problem, the motion of point masses in response to the gravitation of a single massive sphere; it went on to explain (even if only qualitatively in some cases) a wide variety of other phenomena: the precession of equinoxes, the precession of perihelia, the paths of comets, the motions of moons, the rise and fall of the tides, and the fall of apples. By comparison, all past successes of physical theory were parochial. ...

Portrait of Isaac Newton in 1689 (age 46)
by Godfrey Kneller

"Newton's theory did not meet universal acceptance. Despite Newton's own commitment to Unitarian Christianity, some in England, like the theologian John Hutchinson and Bishop Berkeley, were appalled by the impersonal naturalism of Newton's theory. This was unfair to the devout Newton. ...

"Another obstacle to the acceptance of Newton's work was the old false opposition between mathematics and physics that we have seen in a comment of Geminus of Rhodes quoted in Chapter 8. Newton did not speak the Aristotelian language of substances and qualities, and he did not try to explain the cause of gravitation. The priest Nicolas de Malebranche (1638-1715) in reviewing the Principia said that it was the work of a geometer, not of a physicist. Malebranche clearly was thinking of physics in the mode of Aristotle. What he did not realize is that Newton's example had revised the definition of physics.

"The most formidable criticism of Newton's theory of gravitation came from Christiaan Huygens. He greatly admired the Principia, and did not doubt that the motion of planets is governed by a force decreasing as the inverse square of the distance, but Huygens had reservations about whether it is true that every particle of matter attracts every other particle with such a force, proportional to the product of their masses. ...

"Starting already in Newton's lifetime, his theory of gravitation was opposed in France and Germany by followers of Descartes and by Newton's old adversary Leibniz. They argued that an attraction operating over millions of miles of empty space would be an occult element in natural philosophy, and they further insisted that the action of gravity should be given a rational explanation, not merely assumed.

"In this, natural philosophers on the Continent were hanging on to an old ideal for science, going back to the Hellenic age, that scientific theories should ultimately be founded solely on reason. We have learned to give this up. Even though our very successful theory of electrons and light can be deduced from the modern standard model of elementary particles, which may (we hope) in turn eventually be deduced from a deeper theory, however far we go we will never come to a foundation based on pure reason. Like me, most physicists today are resigned to the fact that we will always have to wonder why our deepest theories are not something different. 

"The opposition to Newtonianism found expression in a famous exchange of letters during 1715 and 1716 between Leibniz and Newton's disciple, the Reverend Samuel Clarke, who had translated Newton's Opticks into Latin. Much of their argument focused on the nature of God: Did He intervene in the running of the world, as Newton thought, or had He set it up to run by itself from the beginning? The controversy seems to me to have been supremely futile, for even if its subject were real, it is something about which neither Clarke nor Leibniz could have had any knowledge whatever.

"In the end the opposition to Newton's theories didn't matter, for Newtonian physics went from success to success."


Steven Weinberg


To Explain the World: The Discovery of Modern Science




Copyright 2015 by Steven Weinberg


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