Gravity: Manifest or Mechanical? Revisiting the Leibniz-Clarke Correspondence

[Note: In my seminar on “The Scientific Revolution” this semester, I assigned graduate students to write a blog post that, once revised by the class during a workshop, I would publish on my “Labyrinth of Nature” blog. This is the third piece from that seminar, by Master’s history student  J.D. Wolflick.]

In 1687, Isaac Newton published his Principia Mathematica, a work that many historians consider the culmination of the Scientific Revolution. Its supreme achievement was a universal theory of gravity and inertia that mathematically described both terrestrial and celestial motion

Sir Isaac Newton

Although Newton was able to mathematically describe gravity’s action on bodies, he created a philosophical controversy by being unable to describe the mechanism by which it acted. “But hitherto I have not been able to discover the cause of those properties of gravity from phenomena,” he wrote in the Principia, “and I feign no hypotheses.” Newton’s unwillingness to “feign” a hypothesis for how gravity was able to act at a distance across empty space earned the ire of the Cartesians, to whom Newton’s theory smacked of unintelligibility and the “occult”.  Earlier in the 17th century, the French philosopher René Descartes had proposed that attraction was caused by vortices acting on a very light fluid that filled the space between the planets. This theory became dominant among natural philosophers of the era, and for the Cartesians, anything short of a mechanical explanation was unacceptable. In the early 18th century, the debate reached a high point in an exchange of letters between a proponent of the Cartesian view, German philosopher Gottfried von Leibniz, and the Newtonian, Dr. Samuel Clarke, an English theologian and philosopher. Gravity was only one topic in a debate that included matters such as: the attributes of God as the Creator – and, for Newton, the sustainer – of the universe, the nature of matter and space, and whether or not the universe is infinite and eternal.

Gottfried Wilhelm von Leibniz

Leibniz asserted that Newton’s theory of gravity requires a constant miracle of bodies acting on one another at a distance through the void of space. Clarke replied that gravity can be non-mechanical, but still a natural phenomenon: “But the means by which two bodies attract each other, may be invisible and intangible, and of a different nature from mechanism; and yet, acting regularly and constantly, may well be called natural.” Leibniz then accused Newton of making gravity a “Scholastic occult quality”. Although Leibniz meant this as a slight, Clarke accepted the fact that Newton had only discovered the manifest quality of gravity, but that its cause remained “occult”.The problem of occult qualities in nature was still relevant despite the efforts of the mechanical philosophers. In addition, the meaning of “occult” had changed. As historian Keith Hutchison explains:

Samuel Clarke (1675-1729)

When the seventeenth century opened, “occult” had the double connotation of “insensible” and “unintelligible” … Over the course of the Scientific Revolution, the intelligibility of many insensibles was recognized, and the distinction between the sensible and the insensible lost most of its earlier force … Accordingly, the bond between the two ideas was broken, and “occult” lost the connotation of “insensible,” to retain only that of unintelligibility…But the Cartesians were willing to introduce occult qualities in the old sense of the word into their science only on condition that they were not occult in the new sense, that is, that mechanical explanations could be framed for them.

Newton was perfectly willing to accept an occult cause for gravity if it was regular and predictable. Leibniz would only accept a mechanical, albeit insensible, cause for gravity. Yet if Leibniz were still alive today, he would be disappointed, because he lost the debate. Gravity does indeed act at a distance across empty space with no material intermediary.

By J.D. Wolflick (MA candidate, history)

References:

H.G. Alexander, ed. The Leibniz-Clarke Correspondence (New York: Philosophical Library, Inc., 1956).
K. Hutchison, “What Happened to Occult Qualities in the Scientific Revolution?” Isis, 73 (1982).
A. Koyré, From the Closed World to the Infinite Universe (Baltimore: Johns Hopkins University Press, 1957).

1 Comment to Gravity: Manifest or Mechanical? Revisiting the Leibniz-Clarke Correspondence

  1. July 8, 2013 at 3:30 pm | Permalink

    Revisiting Leibniz’s Einstein-like, geometrical theory of gravity

    http://williameamon.com/?p=382

    “Leibniz asserted that Newton’s theory of gravity requires a constant miracle of bodies acting on one another at a distance through the void of space. Clarke replied that gravity can be non-mechanical, but still a natural phenomenon: but the means by which two bodies attract each other, may be invisible and intangible, and of a different nature from mechanism; and yet, acting regularly and constantly, may well be called natural. Leibniz then accused Newton of making gravity a Scholastic occult quality. ”

    Newton apparently believed that the force of gravity was continually being calculated as
    suggested above to follow the law he had discovered. Thus gravity acted on bodies in a mechanical fashion which Leibniz referred to as being continually “occult” or “miraculous”.

    Leibniz, on the other hand, had a more geometrical concept that, being geometrical,
    foresaw Einstein’s geometrical concept of gravity. In Einstein’s theory, the masses of bodies
    cause the space around them to curve, so as to provide particular arcs of flighty, such as that
    of planets revolving around the sun. He may thus have been so influenced by Keplar, who
    explored the geometrical properties of planetary motion.
    Leibniz accordingly wrote, in his “Mathematical Principles of Natural Philosophy”,

    http://www.archive.org/stream/mathematicalpri01machgoog/mathematicalpri01machgoog_djvu.txt

    [spelling modernized]

    “Whence it [is] that the planets came to be retained within
    any certain bounds in their free spaces, and to be drawn off
    from the rectilinear courses, which, left to themselves, they
    should have pursued, into regular revolutions in curvilinear
    orbits, are questions which we do not know how the ancients
    explained; and probably it was to give some sort of satisfaction
    to this difficulty that solid orbs were introduced. “

    indicating that, while Leibniz believed that Newton’s mechanical theory of gravity
    was wrongly conceived, Leibniz did not at that time know how the force should
    be expressed to accord with his geometrical concept of gravity.

    Dr. Roger B Clough NIST (ret.) [1/1/2000]
    See my Leibniz site at
    http://independent.academia.edu/RogerClough

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