Newton about God’s role in gravity

Isaac Newton’s mechanics is based on a theology: his God is a geometer and an architect who has known how to combine the materials of the system in such a way that result a stable state of equilibrium and a continuous and periodic movement. It is easy to see how precarious and unsound this connection is: while a Voltaire will accept it and make it the foundation of his natural religion, many Newtonians will try to restrict the margin of what is mechanically inexplicable: we will find, in the course of our study, Newtonian cosmogonies, that is to say, solutions to a problem declared insoluble by Newton: how will particles animated by any movement and subject only to the law of Newtonian attraction necessarily group themselves into a system like the solar system? This is the object of Kant and that of Laplace; This one has clearly shown how the movement inaugurated by Newton could not stop at the point where its author had thought to fix it: “I cannot,” he said, “help but observe how much Newton has deviated on this point (the arrangement of the planets) from the method of which he has made such happy applications elsewhere. […] Could not this arrangement of the planets itself be an effect of the laws of motion, and could not the supreme intelligence that Newton brings into play have made it depend on a more general phenomenon? Such is, according to our conjectures, that of a matter scattered in various masses in the immensity of the two. […] Let us go through the history of the progress of the human mind and its errors, we will see there the final causes constantly pushed back to the limits of its knowledge.” (3)

Therefore, many accept Newton’s physics while rejecting his metaphysics. Moreover, in his physics itself, we find a type of intelligibility quite different from the Cartesian type. To explain a phenomenon, for Descartes, is to imagine the mechanical structure of which it is the result; such a mode of explanation risks leading to several possible solutions, since the same result can be obtained with very different mechanisms. Newton declared, repeatedly, that all the “hypotheses” of the Cartesians, that is to say the mechanical structures imagined to explain the phenomena, should be avoided in experimental philosophy. Non fingo hypotheses, that is to say I do not invent any of these causes which, without doubt, can explain the phenomena, but which are only probable. Newton admits no other cause than that which can be “deduced from the phenomena themselves”.

We know that, in stating the law of universal gravitation. Newton did not at all think that he had arrived at the ultimate cause of the phenomena that it explains: he only showed that it is according to the same law that heavy bodies are attracted towards the centre of the earth, that the liquid masses of the seas are attracted towards the moon in the tides, that the moon is attracted towards the earth and the planets towards the sun; the proof of this identity of law rests solely on experimental measurements: for example, Newton’s thesis is demonstrated if, calculating, from Galileo’s laws, the movement which would animate a heavy body placed at the distance of the moon, we find that this movement is precisely that of the moon (in the elements of this calculation between the length of the degree of the terrestrial meridian; and we know how Newton, having accepted a false estimate of this length, almost abandoned his theory, which was on the contrary completely confirmed by a more exact measurement, made later): it is by analogy with terrestrial gravity that he gives the name of gravitation or attraction to the unknown cause of all these phenomena. But he saw so little cause of the phenomena there, that he poses on the contrary, as an unassailable principle, that all action at a distance is impossible; principle that applies to God himself, which leads Newton to declare that God is present at all points of space, and that, as this presence is that of an active and intelligent being, space is the sensorium of God. Gravitation can therefore only be explained by an action of shock and contact; but the phenomena are not sufficiently known for this action to be deduced: it is therefore completely on the fringes of his experimental philosophy and as an example that he supposes an ether in which matter would bathe and whose properties would account, by the impulse, for the phenomena of gravitation.

But this suggestion of the master was not followed at all: “His desires,” wrote d’Alembert in 1751 in the Discourse on the Encyclopedia, “have not been fulfilled and perhaps will not be for a long time. “On the contrary, there was a tendency to consider Newton’s work as entirely completed by the discovery of attraction and to make it an irreducible property of matter, in the same way as the extent or impenetrability; this is obviously the interpretation favored by d’Alembert, who responds to those who accused Newton of having introduced occult qualities: “What harm would he have done to philosophy, by giving us reason to think that matter can have properties that we did not suspect, and by disabusing us of the ridiculous confidence in which we have of knowing them all?” This is just the opposite of the Cartesian spirit: Descartes starts from a clear and distinct idea that makes him intuitively know the essence of matter, and to which nothing can be added; it is by “consulting” this idea that we see the properties that are appropriate to matter. The Newtonians found in their master a very different rule for determining the universal properties of matter: “The qualities of bodies which can neither increase nor decrease,” says the fourth of the Regulae pliilosophandi, “and which belong to all bodies on which it is permitted to experiment, must be held to be qualities of all bodies”; experience and induction alone decide. This rule of Newton is entirely confirmed by the reflections of Locke’s Essay on Substance: he too admits that substance is known to us only by a mass of properties that experience alone shows us to be fixedly linked together. It is then permitted and even ordered to attribute to matter attraction, the coefficients of which Newton showed are the same, whatever the bodies considered; it is therefore measurement which alone assures us of this identity of a quality: “The first springs that nature uses,” says Voltaire, “are not within our reach when they are not subject to calculation.”

Attraction is therefore, for Newtonians, an incontestable property of matter, although we cannot explain it; Voltaire is the interpreter of a very widespread opinion, saying that physics consists, starting from the very small number of properties of matter that the senses give us, in discovering by reasoning new attributes such as attraction: “The more I reflect on it,” he says, “the more I am surprised that we fear to recognize a new principle, a new property in matter. It may have them to infinity; nothing is alike in nature.” (4)

In this way again, the philosophy of nature frees itself from the philosophy of the mind; the primitive data with which nature is interpreted are data of experience, impenetrable to the mind, for which one cannot find the reason. We will see the series of difficulties which arose from this empiricism during the century.

By its philosophical side, Newton’s science leaves us in short in a great uncertainty: its mechanism can orient us as much towards theology as towards materialism; the point where the explanation stops is not clearly marked, nor whether the mind can go further than the opaque qualities given to experience; there is a surprising contrast between the precision of the results and the lack of firmness of the principles: this contrast will be the underlying theme of a good part of philosophy in the 18th century.

References

3. Quoted by Busco, Les Cosmogonies modernes, p. 52.
4. Philosophie de Newton, 2nd part.

Source: Émile Bréhier(1951). Histoire de la philosophie, Presses Universitaires de France. Translation and adaptation by © 2024 Nicolae Sfetcu