Action at a Distance in Early Modern Natural Philosophy
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KeywordsCausation Gravity Force Magnetism Occult influence Power
are perhaps some immaterial substances, or some spiritual rays, or some accident without a substance, or some kind of species intentionalis, or some other I know not what, the means by which this [gravity] is pretended to be performed?” (Alexander 1956, p. 94.)
Leibniz’s point was that whatever explanation is proposed, unless it involves bodily contact action, it is action at a distance and ipso facto nonsensical and untenable – after all, how could “spiritual rays” or anything immaterial cause any body, much less a planet, to move? Samuel Clarke, defending Newton against Leibniz, simply insisted that “the means by which two bodies attract each other may be invisible and intangible, and of a different nature from mechanism” (Alexander 1956, p. 53); or, as he wrote in his Third Defence of the Immateriality of the Soul (1706): “God himself is an immaterial being, and… he can move matter, though he does not impel it by contact… therefore… it is manifest that there are other ways of moving it [matter] besides that of impelling by contact” (Clarke 1738, v. iii, p. 848). In the seventeenth century, action at a distance was largely seen as unacceptable and was categorically rejected by scholastic Aristotelians and by mechanical philosophers alike. By the eighteenth century, however, Newton’s acceptance of actions at a distance, together with the perceived success of his gravitational theory, resulted in a period when actions at a distance became widely accepted in physics, before being rejected again from the middle of the nineteenth century onward (Schofield 1970; Thackray 1970; Henry 2011, 2019).
Action at a Distance in the Renaissance Revival of Natural Magic
Aristotle made a number of explicit comments to the effect that bodies could only act on one another by contact (e.g., Physics, VII, 2, 243a 32–35, and VIII, 4, 255a 34–35; De generatione et corruptione, I, 6, 322b 28–29, and 323a 33–34). This was endorsed by Thomas Aquinas, and it subsequently became axiomatic in scholastic natural philosophy that “no agent can operate immediately where it is not” (e.g., Summa Theologica, Part III, Q. 64, Art. 1, Obj. 3). The alternative belief that bodies could in some cases act on one another at a distance, without any intervening material connection, was generally confined to the magical tradition. Perhaps connected to superstitious beliefs in the so-called evil eye (the ability attributed to some people to curse or blight someone merely by looking at them), vision became a model for action at a distance. This went hand-in-hand with the extromission theory of vision, which supposed that vision was dependent upon something flowing out of the eye (the eye illuminates the scene like a torch), rather than on something arriving at the eye (the intromission theory). Be that as it may, the idea that all things, not just things capable of seeing, gave out immaterial “rays” which conveyed some kind of power became a mainstay of learned magic. The seminal work was De radiis stellarum (On the rays of the stars); significantly, this was also known by the more general title, De theoria artium magicarum (On the theory of the magical arts). Attributed to the Arab philosopher, Al-Kindi (801–73), this may have been written later by an unknown Latin scholar (Adamson 2007, p. 188). According to this influential author: “…each thing in this world, whether substance or accident, produces rays in its own way like the stars… Hence each place in this world contains the rays of all the things which actually exist in it” (Adamson and Pormann 2012, p. 226). The eminent medieval historian, David Lindberg, summed up the natural philosophy deriving from this tradition as one in which “every creature in the universe is a source of radiation and the universe a vast network of forces” (Lindberg 1986, p. 13). These forces, however, were conceived of as immaterial sources of influence and power. In current historiography, histories of force have focused, in a whiggish or presentist way, almost entirely on mechanical force, that is to say, forces generated by moving bodies in impact, or in collision with other bodies. Earlier beliefs in immaterial forces, including magnetism, have barely even been noticed by historians – Lindberg and Mary Hesse being notable exceptions (Hesse 1963).
The magical belief in immaterial forces was one of many aspects of natural magic that became more respectable during the Renaissance, as a result of the (mistaken) belief that the Neoplatonic writings attributed to Hermes Trismegistus represented some of the most ancient wisdom known to later ages. The tenth of the Hermetic treatises translated by Marsilio Ficino, “The Key,” includes the claim that “energies are like rays of God, natural forces like rays from the cosmos, …and the energies work through the cosmos and upon mankind through the natural rays of the cosmos” (Copenhaver 1992, p. 35). In his own attempt to rehabilitate magic, Three Books on Life (1489), Ficino emphasized the immaterial nature of rays: “all the rays of all the stars penetrate in a moment the mass of the earth (which is as a point in relation to the sky) and with consummate ease straight to the center” (Ficino 1998, p. 321). After listing some common occult effects, he draws on the old analogy with vision: “In the light of all this, are you going to deny that the celestials with the rays of their eyes with which they both look at us and touch us, achieve wonders in an instant?” (Ficino 1998, p. 325).
It seems clear that the magical belief in the possibility of action at a distance enjoyed a revival in the Renaissance and that this carried over into the early modern period. Actions at a distance featured prominently, for example, in Heinrich Cornelius Agrippa’s De occulta philosophia (1533), Girolamo Fracastoro’s De sympatia et antipathia rerum (1546), De abditis rerum causis (1548) of Jean Fernel, Giambattista della Porta’s Magia naturalis (1558, expanded in 1589), and the Del senso delle cose e della magia naturale (1620) of Tommaso Campanella.
Partly as a result of its association with magic, and perhaps even more as a result of its thorough rejection from late modern physics, historians of science have scarcely looked into the history of ideas of action at a distance. Indeed, there is still enormous resistance among modern scientists, philosophers, and even some historians to accepting that any right-thinking person could ever have believed that an “agent can operate immediately where it is not.” Rejection of action at a distance has been a mainstay of modern physics since the middle of the nineteenth century and was reinforced by Einstein’s authoritative dismissal of “spooky action at a distance” (Musser 2016). This seems to have resulted in genuine distaste for the very idea of action at a distance, and rejection of the concept has become so entrenched that many modern commentators refuse to accept that attitudes to action at a distance may have been less unanimously held in the past. Many modern scholars feel the need to deny that any significant historical thinker ever subscribed to belief in action at a distance. So, it has been suggested, for example, that Ficino used the concept of “rays” as a way of denying action at a distance: “Sprits, rays, and figures all provide physical and cosmological solutions to the problem of action at a distance” (Copenhaver 2015, p. 254). For Ficino’s more philosophically orthodox contemporaries, however, a body could only act upon another body by contact action, and to suggest that a body acted upon another body without making contact, but by means of spirits or rays, was to invoke actions at a distance. So, for scholastic contemporaries, Ficino’s rays did not solve the problem of action at a distance but raised it as a problem.
pursuing his studies of mutual forces of attraction (leading up to universal gravity) while writing the Principia… if he could not bring himself to believe in forces acting at a distance? The answer is that the “Newtonian style” permitted him to explore the consequences of assuming a force to be centripetal or to act at a distance, without requiring any adherence to a belief in the real existence of such forces. (Cohen 1982, p. 61)
Evidently, it was Cohen himself who “could not bring himself to believe in forces acting at a distance” and desperately felt the need to convince readers that Newton’s obvious belief in action at a distance must be merely illusory (see also Cohen 1980, and Cohen’s “Guide to Newton’s Principia” in Newton 1999).
Given this distaste for actions at a distance among modern commentators, the history of concepts of action at a distance is very underdeveloped. Recent work has tended to concentrate on Newton’s belief in actio in distans and the English background to Newton’s acceptance of this way of thinking (Henry 2011, 2019; Ducheyne 2014). In what follows, therefore, we will simply focus on this.
Action at a Distance in English Natural Philosophy Before Newton
The body of Nature is most elegantly and truly represented as covered with hair; in allusion to the rays which all objects emit; for rays are like the hairs or bristles of nature; and there is scarcely anything which is not more or less radiant. This is very plainly seen in the power of vision, and not less so in all kinds of magnetic virtue, and in every effect which takes place at a distance. For whatever produces an effect at a distance may be truly said to emit rays. (Bacon 2013, pp. 829–30)
And in optical rays and sounds and heat and some other things that work at a distance, it is probable that the bodies in between are affected and altered: the more so as this requires a medium suited to carrying such an operation. But magnetic or connective force is indifferent as to medium, and the force is not impeded in any kind of medium. (Bacon 2000, p. 169)
So, in some cases what looks like action at a distance is in fact brought about by successive transmission of the effect through intervening bodies; but there are other cases, however, such as magnetism, or “connective force,” which are genuine cases of actio in distans.
There are other powers which work at a distance, albeit a very small distance. Few have yet been noted, though there are more than men imagine. For instance (to take examples from common objects), amber or jet attracts straws, a bubble bursts another bubble when it gets close to it, certain purgatives draw down rheum, and so on. And the magnetic power which draws iron to a magnet or draws magnets to each other works within a certain range of power, though a small one; whereas if there is a magnetic power proceeding from the earth itself (evidently just below the surface) on to an iron needle and affecting its polarity, the effect would be working at a great distance.
Again, if there is any magnetic force operating by agreement between the globe of the earth and heavy things, or between the globe of the moon and the waters of the sea (which seems very likely in the high and low tides twice a month), or between the starry heaven and the planets, by which they are called up and raised to their apogees; all these things would be operating at very great distances. (Bacon 2000, p. 184)
It seems likely that Bacon’s speculations about the cosmic role of magnetic attraction derive from the work of his fellow countryman, William Gilbert, author of De Magnete (1600) (Hesse 1963). It is important to note, however, that Gilbert was one of those thinkers who continued to deny the possibility of action at a distance. Rather than invoke distant actions, Gilbert insisted that magnets were animated and simply moved themselves toward one another (or to a piece of iron), in the same way that an animal can move itself. So, there is no physical force of attraction between magnets – it just looks that way because they always rush toward one another, resulting in what Gilbert calls (not insignificantly) coition (Wang 2016).
It is clear that Bacon, although recognizing the value of Gilbert’s research into magnets, saw action at a distance as less problematic than supposing all magnets have souls. Bacon was not alone, and all subsequent followers of Gilbert turned his animated magnets into magnets capable of acting at a distance. Johannes Kepler, for example, who used magnetism to provide a physical explanation for the elliptical orbits of the planets, wrote: “If you substitute for the word ‘soul’ the word ‘force’, you have the very principle on which the celestial physics of the treatise on Mars etc. is based” (Kepler  1981, p. 199). Gilbert had shown the earth to be a giant magnet, and Kepler assumed the other planets were too. Kepler wrote of “magnetic filaments” extending from the Sun to the planets, and carrying the planets around the Sun as it rotates on its axis, but he describes these filaments as immaterial and therefore was invoking action at a distance (Stephenson 1987, pp. 146–75).
But William Petty had already been led to this same suspicion in 1674, but in his case he suggested the causes were not unknown, but were magnetic attractions and repulsions.
many things lead me to have a suspicion that all phenomena may depend on certain forces by which the particles of bodies, by causes not yet known, either are impelled toward one another and cohere in regular figures, or are repelled from one another and recede. (Newton 1999, pp. 382–3)
Newton and Action at a Distance
Later that same year, Robert Hooke wrote to Newton to ask his opinion of a hypothesis which he had developed as a culmination of the Gilbert-and-Bacon-inspired attempt to understand the motions of the tides, the planets, and so forth. In a lecture to the Royal Society delivered in 1666, Hooke declaimed:
is expanded to double or treble or even a hundred or a thousand times its normal space, which would hardly seem to be possible if the particles of air were in mutual contact; but if by some principle acting at a distance [the particles] tend to recede mutually from each other, reason persuades us…. (Newton 1962, p. 223; see also Henry 2011)
He went on to propose that all the Keplerian planetary motions could be understood simply by assuming an inertial movement of the planet bent into an orbit around the Sun by an “attractive principle” located in the Sun. Hooke did not explicitly mention action at a distance, but there is no hint that he is thinking in terms of Cartesian plenist explanations and no attempt to provide a mechanical explanation of the supposed attraction between the Sun and the planet. From here Newton went on to write the Principia, and as R. S. Westfall pointed out, from then on “Newton applied action at a distance to virtually all the phenomena of nature” (Westfall 1980, p. 388).
I have often wondered why the planets should move about the sun according to Copernicus’s supposition, being not included in any solid orbs… nor tied to it, as their centre, by any visible strings…. (Gunther 1930, p. 265)
This might seem to be a clear enough indication that Newton accepted actions at a distance, and yet in his “Guide to Newton’s Principia,” I. B. Cohen wrote that:
Have not the small particles of Bodies certain powers, Virtues, or Forces, by which they act at a distance, not only upon the Rays of Light… but also upon one another for producing a great Part of the Phaenomena of Nature? (Newton 1979, pp. 375–76.)
It should be clear (given that Newton actually says these forces act at a distance and that, as we have seen, Newton first explicitly accepted actions at a distance when he supposed short-range repulsions between atoms could explain extreme rarefaction) that what we are seeing in this quotation from Cohen is a clear example of what was said before about the extreme resistance displayed by many scholars to the very idea that Newton accepted actions at a distance. The evidence in Newton’s own works says the opposite to what Cohen avers.
Such forces, according to Newton, are sufficiently short-range in their action… that they do not raise a major problem of understanding their mode of action. They do not, in other words, fall into the category of the forces acting at a distance. (Newton 1999, p. 61)
Newtonianism and Action at a Distance
Newton’s subsequent influence upon the development of the natural sciences was unprecedented, and one of the most remarkable aspects of that influence was the fact that he brought actions at a distance out of the despised magical tradition and established them as a routine part of mainstream physics for over a century (Schofield 1970; Thackray 1970).
Elsewhere, Kant made it perfectly explicit that he accepted Newtonian actions at a distance:
It is commonly supposed that Newton did not at all find it necessary for his system to assume an immediate attraction of matter, but, with the most rigorous abstinence of pure mathematics, allowed the physicists full freedom to explain the possibility of attraction as they might see fit… But how could he ground the proposition that the universal attraction of bodies, which they exert at equal distances around them, is proportional to the quantity of their matter, if he did not assume that all matter, merely as matter, therefore, and through its essential property, exerts this moving force?… Thus, one cannot adduce this great founder of the theory of attraction as one’s predecessor, if one takes the liberty of substituting an apparent attraction for the true attraction he did assert, and [if one] assumes the necessity of an impulsion through impact to explain the phenomenon of approach. (Kant 2004, pp. 52–3)
There were many practicing natural philosophers who agreed with Kant and who saw themselves as continuing along the path that Newton had opened up in the Principia and in the Queries to his Opticks (Thackray 1970; Schofield 1970). For example, at the beginning of the nineteenth century, when John Dalton, founder of the modern theory of atomism, tried to understand why the different gases known to compose the atmosphere did not separate out from one another according to their weights (these gases were known to be not in chemical combination with one another but simply mixed together), he turned to a Newtonian explanation. He supposed that the particles of each gas mutually repelled one another, but had no effect on the particles of another gas. So, each gas spread itself out through the atmosphere (by its own mutually repelling nature), and there was no layering by weight, as there would be with immiscible liquids. But this assumption, in turn, led to the conclusion that the atoms of each gas must be qualitatively different from one another (because atoms of one gas did not affect atoms of a different gas), and so Dalton was able to reject the age-old assumption that all atoms were alike (differences in bodies being only the result of the shape, size, and arrangement of the otherwise uniform atoms) and to suggest that each of the new elements discovered by Antoine Lavoisier and subsequent chemists had a characteristically different atom. Dalton’s conclusion clearly went beyond Newton (who believed all atoms were qualitatively alike), but he started out by assuming Newtonian actions at a distance (Thackray 1972; for similar examples of eighteenth-century Newtonians assuming actions at a distance, see Schofield 1970 and Thackray 1970).
The most common objection to immediate action at a distance is that a matter cannot act immediately where it is not. When the earth immediately impels the moon to approach it, the earth acts on a thing that is many thousands of miles away from it, and yet immediately; the space between it and the moon may well be viewed as completely empty. For even though matter may lie between the two bodies, it still contributes nothing to this attraction. It therefore acts immediately at a place where it is not, which is apparently contradictory. In truth, however, it is so far from being contradictory that one may rather say that every thing in space acts on another only at a place where the acting thing is not. (Kant 2004, p. 51)
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