## Experiments or other certain truths Isaac Newton

The expression "experiments, or other certain truths" was penned by Isaac Newton (164220—1727). His scientific method consisted of what he himself called experiments and observations from which conclusions can be drawn by means of induction and against which contradictions are tolerated only if they are also based on "experiments or other certain truths."21 The certain truths can be understood in contrast to hypotheses, which are completely inappropriate for experimental philosophy.22 However, this section will show how problematic the relationship between experimental results and predetermined certain truths was, even for Newton. Establishing a connection of absolute time and absolute space with the existence of God proved to be difficult and provocative.

In Newton's account of the basic principles of mechanics, Philosophiae Naturalis Principia Mathematical one finds sentences that are often cited by classical physics as the typical definition of time. Newton prefaces his definition with the comment that the generally well-known concepts of time, space, place, and motion actually would not require an explanation. Due to human perception, however, prejudices could easily arise that he thought he could eliminate by distinguishing between absolute, true, and mathematical, on the one hand, and relative, apparent, and common, on the other. Thus, he always distinguishes between absolute and relative space, absolute and relative place, and absolute and relative motion. Only in the case of time, which he defines first, does he list all three distinguishing criteria:

I. Absolute, True and Mathematical Time, of it self, and from its own nature flows equably without regard to anything external, and by another name is called Duration: Relative, Apparent, and Common Time is some sensible and external (whether accurate or unequable) measure of Duration by the means of motion, which is commonly used instead of True time; such is an Hour, a Day, a Month, a Year.24

Correspondingly, absolute space "without regard to any thing external, remains always similar and immovable," while relative space is "some moveable or measure of the absolute spaces," which we customarily perceive to be immovable space.25 Place and motion are each defined in relation to absolute or relative space.26

Even though Newton favors an empirical, inductive method in a conscious distancing from Descartes' deductive method that is based on principles of reason, he is not completely successful in deriving absolute time. He says that, in astronomy, absolute time is measured by the motion of the heavenly bodies, but he concedes that it is possible that no uniform motion exists at all on which time could be precisely measured: "All motions can be accelerated or retarded, but the True or equable progress, of Absolute time is liable to no change."27 Absolute time therefore remains a postulate or, at least, a theoretical value, which is indeed defined, but does not correspond to direct experience.

Likewise, the distinctions between relative and absolute with regard to space, place, and motion are not directly accessible.

For from the positions and distances of things from any body consider'd as immoveable, we define all places: and then with respect to such places, we estimate all motions, considering bodies as transfer'd from some of those places into others. And so instead of absolute places and motions, we use relative ones; and that without any inconvenience in common affairs: but in Philosophical disquisitions, we ought to abstract from our senses, and consider things themselves, distinct from what are only sensible measures of them. For it may be that there is no body really at rest, to which the places and motions of others may be referr'd.28

Absolute values are, at the most, only approximately accessible by means of observations and experiments. How then can a distinction be made between an absolute inert space and a system in motion? Newton gives an example: When a container filled with water revolves around its own axis, the water surface assumes a concave shape, i.e., a curve that rises towards the walls of the container, as a result of centrifugal force, while it forms a flat plane in a stationary container. Based on centrifugal force, an empirical distinction can thus be made between the system in motion and the inert system. This distinction remains relative, however, because it is impossible, by means of measurements, to distinguish the absolutely inert space from all other systems moving uniformly relative to inert space.

Newton admits that distinguishing true values from apparent ones is quite difficult, yet "not altogether desperate,"29 since there are aids for properly distinguishing the causes and effects of true or apparent motions, the proper use of which is the instructional purpose of the Principia. To make no distinction between absolute and relative values would be almost morally reprehensible; whoever confuses one with the other both violates the Holy Scriptures and also sullies mathematics and philosophy.30

Newton distinguishes between eternity and infinity in the same way that he differentiates between space and time. What eternity is for time, infinity is for space. The value pairs appear to stand in extrapolative relationship to each other, so that eternity and infinity always appear to be the highest powers of time and space. Correspondingly, God's duration lasts from eternity to eternity, and God's presence from infinity to infinity.31 Yet, this conceptual separation is not always applied consistently. When he says, as an exclusive property of stationary places, that they maintain the same relative position "from infinity to infinity"—i.e., they always remain stationary32—then "infinity" should not be understood here only spatially, but also temporally.33 Both eternity and infinity are conceived as being in continuity with time and space; Newton does not consider the possibility of a fundamentally different dimensionality.

From a further reading of Newton's works, one gets the impression that his concern is actually more about the problems of absoluteness and relativity of space, whereas the concept of absolute time initially remains unchallenged. Indeed, the physical realization of absolute time appears to be simpler than that of absolute space. By synchronizing the time-measuring instruments of all observers, a coordination of time within different frames of reference appears to be attainable. With regard to space, on the other hand, the transition from one reference system to another requires a transformation. Mathematically, this corresponds to the conversion of the coordinates of one frame of reference to the coordinates of another frame of reference. In classical mechanics, one uses the Galilean Transformation, whose equations for rectilinear and uniform motion along the X-axis read as follows:34

Time appears to avoid the problems that are associated with space. As the factor t in the equations, it can be used for calculations without requiring a description of what absolute and relative time really are. The fact that the equations of motion allow solutions with both positive and negative time (t and — t), i.e., that they allow time to be considered as reversible, did not harm classical mechanics. The differences between past, present, and future had to appear as an illusion in this system. This must have been considered to be only an insignificant shortcoming, however, when contrasted to the huge gains of a mathematical description of the universe that includes time, united Copernican and Keplerian astronomy with the Galilean concept of acceleration, and deterministically and causally explained the movement of earthly and heavenly bodies by means of a single force—gravity.35

Edwin A. Burtt points out that Newton's distinction of absolute and relative motion using the concept of force as criterion is untenable.36 When Newton claims that wherever force is exerted, absolute motion occurs,37 he inadmissibly presumes that one can also reverse the argument of an effect in the direction of a cause into an argument of a cause (i.e., force) in the direction of an effect.38 Burtt sees the basis for this conclusion by Newton as being in the contemporary idea of force as a phenomenon having an autonomous existence that precedes all effects and is independent of them. Burtt speaks of animistic characteristics from which the scientific theory of force was only gradually cleansed. Because there is no doubt of Newton's theological ambitions, however, I believe it is more reasonable to assume that Newton defined the physical concept of force within the framework of the theological notion of divine action.39

Burtt, who assumes that Newton was influenced by the Cambridge Pla-tonist Henry More,40 sees another inconsistency in the fact that Newton relates the movement of bodies to absolute space and absolute time.41 Because absolute space and absolute time are infinite and homogenous entities and thus cannot be distinguished within themselves, bodies can certainly move in absolute space and in absolute time, but the motion is only noticeable in relation to other bodies and not in relation to absolute space and absolute time. According to Burtt, mathematics and physics were not decisive here for Newton, but rather his theological conviction that, ultimately, time and space have religious significance. He substantiates this with quotations from the General Scholium, among other things, which Newton added to the second edition of the Principia—according to which God, existing forever and everywhere, constitutes time and space.42 "Absolute space for Newton is not only the omnipresence of God; it is also the infinite scene of the divine knowledge and control."43

In Opticks, Newton speaks of a divine sensorium in connection with absolute space, which suggests an understanding of divine consciousness as the highest frame of reference for absolute motion. Whenever the connection to this divine frame of reference is abolished, however, absolute space and absolute time become empty categories. What remain are ideas of a mechanical universe that functions like a clock and a nature that is despiritual-ized. Burtt already foresees this development.44 Within the framework of eco-theological concepts, it has been emphasized repeatedly that Newton's thoughts paved the way for the misuse and exploitation of nature. In my opinion, however, it was not Newton's thinking per se that necessarily re-

suited in damage to the environment. The threat to a nature that is understood mechanically by human beings ruling over it is more likely a consequence of the dissolution of the synthesis of science and theology that still existed in Newton.45

Natural scientific, as well as theological work, takes place in a social reality. The historian John Brooke describes what this means for Newton's work. On the one hand, Brooke points to the sociopolitical interpretative potential of Newton's ideas;46 and, on the other hand, he examines the merging of science and theology in Newton's thinking.47 He contradicts the idea that, by the end of the seventeenth century, a so-called scientific revolution caused the development of modern science, with a sharp division between philosophy and theology on the one side and natural science on the other. Indeed, Newton's century saw an increasing differentiation between theology and science, but scientific findings were still being presented in theological terminology, and divine characteristics were still being explained in physical terms.48 Brooke elucidates this by using Newton as an example: Newton was concerned with explaining natural phenomena as mechanical processes as well as expressions of divine will. He rejected the alternative to the latter, namely that the cause of an event is inherent to physical matter. His thinking therefore adopted an ambiguity that could lead to both theis-tic and deistic interpretations.49 In his laws, Newton saw proof of the constant presence of God; however, these laws could just as easily apply to the notion of an absent clockmaker.50 In this ambiguity, Newton's theology also bears the seed of its own destruction: Against Newton's will, God becomes a "god of the gaps," who is finally dethroned by Pierre de Laplace. The fact that Newton thought the Trinitarian dogma was irrelevant51 is consistent with the premises portrayed here. As he matured, his Arian conviction grew until he became convinced that true religion and world peace would be possible only when the doctrine of the Trinity was eradicated.52 Correspondingly, Newton also did not develop a Christology that could have influenced his religious-philosophical thoughts in Principia and Opticks.53

The observation of societal and philosophical interconnections raises the difficult question of what actually caused what. Did the sociopolitical climate influence natural philosophy or did science influence politics? Did Newton's image of God leave its mark on mechanics or did mechanics shape his image of God? Brooke makes a plea for the latter alternative: Newton created a God for himself according to his own understanding54— "[t]he rationalism characteristic of his scientific work was not so much deflected as reflected in his biblical studies."55 At the same time, Brooke concedes that theology influenced the concept of space and also fundamentally shaped the content of the concepts of law and force.56 In any case, one should note that the purely mathematical consequences of Newton's laws could certainly be effective theologically: The equations of motion must be solved using differential calculus. In order to obtain in this process only one solution, instead of an infinite number, the initial conditions of the system must be defined. Similarly, the theological interpretation of a deterministic mechanics for the universe requires a God who is understood as the one determining the initial conditions.

How, then, is the concept of time to be understood against this backdrop? Burtt, who sees this as a linguistic question rather than one of physics, indeed attributes ambiguity to Newton's definition of absolute time, but he sees it as a brilliant use of language.57 Whether or not time can actually flow remains unclear. Is it not instead the case that things and events flow in time? Does a river flow, or is it water molecules that flow? Two things are hidden within this uncertainty: On the one hand, absolute time appears to be a homogenous mathematical continuum that extends from an infinite past into an infinite future and is always conceived as a whole. Thus, however, it can hardly be distinguished from space. On the other hand, it is a sequence of moments of which only the prevailing now exists; time thus shrivels into a razor-thin mathematical border between past and future, a boundary that flows uniformly in time, but that cannot be time itself. Burtt advocates the idea that Newton wants to combine these two understandings of time by describing time as an infinite continuum with a language that belongs to the understanding of time as a boundary that is continuously moving forward.58 Despite all of its brilliance, however, this scientific concept of time has lost contact with the duration that is experienced as being direct.59

I have given much attention to Newton's accounts of the relationship of God to absolute space and absolute time, as described in the General Scholium and in some sections of Queries 28 and 31 in Opticks. However, I do not wish to mislead the reader into thinking that it was Newton the the-ologian60 rather than Newton the mathematician, the physicist, and the astronomer who accomplished pioneering scientific work. Thus, the General Scholium, which was based on the study of planets and gravitation and dealt with the role and necessity of God, was not part of the first edition of the Principia. Newton, who was over seventy years old at the time, wrote it only for the second edition in 1713, as a concession to those pious souls who were upset by a mechanical explanation of the universe that could be interpreted as being atheistic.

In the General Scholium, Newton uses a type of cosmological proof of the existence of God: "This most beautiful system of the sun, planets, and comets, could only proceed from the counsel and dominion of an intelligent and powerful Being."61 This being is God in the sense that it rules over everything. The word "God" is understood relationally,62 as Lord over servants: "It is the dominion of a spiritual being which constitutes a God."63 God's duration lasts from eternity to eternity and God's presence from infinity to infinity; however, "he is not duration or space, but he endures and is present. . . . [H]e constitutes duration and space."64 God is omnipresent, not only virtually, but also substantially.65 God necessarily exists forever and everywhere. All bodies move in God without suffering resistance from the divine omnipresence.66 From a human perspective, three attributes should be given to God, namely, "dominion, providence, and final causes."67 Should God also therefore be identified as the cause of the gravity that determines the phenomena of heaven and earth? Newton expresses himself cautiously on this matter. Up to this point, he says that he has not been able to derive the causes of the properties of gravity empirically, and he rejects hypotheses. Here, one finds the sentence that is often cited out of context: "Hypotheses non fingo." (I do not manufacture hypotheses).68

Newton had already expressed the same thoughts towards the end of Query 28 in Opticks, where he described the main task of natural philosophy as being "to argue from Phenomena without feigning Hypotheses, and to deduce Causes from Effects, till we come to the very first Cause, which certainly is not mechanical . . ."69 Even if natural philosophy does not provide direct access to this first cause, it does lead to close proximity and is therefore quite valuable. The consideration of natural phenomena suggests that there is a Being incorporeal, living, intelligent, omnipresent, who in infinite Space, as it were in his Sensory, sees the things themselves intimately, and throughly [sic] perceives them, and comprehends them wholly by their immediate Presence to himself: Of which things the Images only carried through the Organs of Sense into our little Sensoriums, are there seen and beheld by that which in us perceives and thinks.70

There is a similar reflection at the end of Query 31. In a clear allusion to the biblical story of creation, Newton considers it to be probable that God "in the beginning form'd Matter in solid, massy, hard, impenetrable, moveable Particles, ... no ordinary Power being able to divide what God himself made one in the first Creation."71 These particles can indeed be combined into new shapes, but their stability is the basis for all continuity of natural phenomena. The particles are controlled by forces of natural laws, thanks to which the world is able to maintain itself, with the exception of a few irregularities that can increase "till this system wants a reformation."72 God can change the natural laws and create worlds that have different natural laws in different parts of the universe.73 An examination of the animal kingdom supports the sense that the ruling order there can be the effect of nothing else than the Wisdom and Skill of a powerful ever-living Agent, who being in all Places, is more able by his Will to move the Bodies within his boundless uniform Sensorium, and thereby to form and reform the parts of the Universe, than we are by our Will to move the Parts of our own Bodies.74

Precisely those passages that speak of a sensorium of God75 provided rich material for discussion. They repeatedly formed the background for the controversy concerning the absoluteness of space and time between Newton's disciple Samuel Clarke and the philosopher Gottfried Wilhelm Leibniz, which we will discuss in the next section.

The following concepts76 are suitable for a summarizing characterization of Newton's concept of time: Absolute time is qualified as universality. Its uniformity (symmetry) makes it quantifiable and divisible.77 On the one hand, time experiences an idealization in the sense of a lack of concrete content and an abstraction of the empirical experience of time. On the other hand, as the "arena" for the actions of the omnipotent and omnipresent God, it experiences a realization by being filled with determined (theological) content.

"Quelque chose de purement relatif: un ordre des Coexistences"—Leibniz's Criticism "Something purely relative and an order of the co-existences"—with these words, Gottfried Wilhelm Leibniz (1646-1716) describes his concept of space. Something corresponding also applies to time, he adds. Time is also relative and to be understood as an order of succession.78 Leibniz developed these ideas during a dispute with Samuel Clarke (1675—1729) over the interpretation of Newton's ideas.79

The argument between Leibniz and Clarke included five letters by each of the two adversaries and ended, without reaching any consensus, upon the death of Leibniz in 1716.80 It began in November 1715, with a letter from Leibniz to Caroline, Princess of Wales, which was followed by Clarke's response.81 The questions at issue, which are then repeatedly addressed in further correspondence, already surface in this first letter. The main accusations of Leibniz include materialism—"Many will have human souls to be material: others make God himself a corporeal being"82—a limitation of God's sovereignty—the discussion about space as God's sensorium makes God dependent upon this—and a false understanding of God's actions—

Newton's God is a poor clockmaker, for this God is constantly having to intervene and correct creation. On the contrary, Leibniz's God, from the beginning, put into motion the interplay of the natural forces according to "le bel ordre preetabli,"83 so that miracles effected by God are not mandated by a nature needing correction, but rather can be understood solely as acts of grace.

The least reconciled issues are the differences in the question of the sen-sorium Dei. While Leibniz steadfastly defines sensorium as a perceptive organ and, for this reason, accuses Clarke and Newton of misunderstanding space as the sensory organ of God, Clarke explains over and over that Newton is concerned only with an analogous use of the concepts: space (and, correspondingly, also time) are only like sensory organs. Instead, the omnipresent God perceives all things "by his immediate presence to them, in all space wherever they are, without the intervention or assistance of any organ or medium whatsoever."84

To the accusation of making God look like an inferior craftsman, Clarke replies that God is more than just a mechanic. Precisely the assertion that God is the source and the constant preserver does justice to God's true greatness and prevents God's expulsion from the world; " 'tis not a diminution, but the true glory of his workmanship, that nothing is done without his continual government and inspection."85 At the end of this initial round of discussions, two features of the debate have already crystallized that will be reinforced over the course of the correspondence. First, the reader, who hopes for an intensive illumination of the phenomenon of absolute time, tends to be disappointed, because the discussion revolves primarily around space. It must be noted, however, that what is said about space also applies to time.86 Second, different conceptions of divine action come to light. The contributions of the two adversaries to the discussion of this question are extensive and deal repeatedly with the role of God's intervention in natural occurrences in relation to divine perfection. I believe that physical, cosmo-logical, or philosophical theses are not really the issue here, but rather that the core of the debate centers on a difference in theological outlook. An interpretation wishing to do justice to the character of the correspondence must devote great attention to the theological premises. A key to understanding lies in the consideration of what each author considers significant with regard to God's perfection. While Newton and Clarke each predominantly focus on the power of God,87 Leibniz always argues from the standpoint of God's wisdom.8

The power of Newton's and Clarke's God is expressed especially in divine omnipresence.89 This connection of power, eternity, and omnipresence forces Clarke to declare that absolute space and absolute time are necessary attributes of God's divinity. In contrast, the primacy of wisdom in Leibniz's concept of God leads to the idea of the beauty of preestablished harmony.90 It is God's wise foresight that makes a corrective intervention in the mechanics of the world unnecessary. In divine wisdom, God does nothing unintentionally; all God's actions are well founded.91 Leibniz's aversion to the existence of a vacuum should be understood in light of the principle of God's wisdom—namely, the less matter that exists, the fewer objects would be available for the goodness of God. God's work would then be incomplete, which would contravene God's wisdom and the axiom of sufficient cause that is asserted by Leibniz.92

In his second reply, Clarke concedes that the continual need to repair the world's mechanism can be understood only in relative terms. He says that what to human observation appears to be disorder is, in reality, the expression of God's perfect idea. In the same breath, he assures the reader that God is neither "a mundane intelligence" nor "a supramundane intelligence," but rather "an omnipresent intelligence, both in and without the world. He is in all, and through all, as well as above all."93

In his third letter, Leibniz directly attacks Newton's space-time concept. He considers the concept of space as "a real absolute being"94 to be contradictory. Such space would have to be eternal and infinite, which is why it is also erroneously conceived of as God or, at least, as an attribute of God. However, because space consists of parts, it cannot belong to God in such a manner. For this reason, Leibniz explains: "As for my own opinion, I have said more than once that I hold space to be something merely relative, as time is; that I hold it to be an order of coexistences, as time is an order of

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