On Kant's first insight into the problem of space dimensionality and its physical foundations
aa r X i v : . [ phy s i c s . h i s t - ph ] A p r ON KANT’S FIRST INSIGHT INTO THEPROBLEM OF SPACE DIMENSIONALITYAND ITS PHYSICAL FOUNDATIONS
F. Caruso , & R. Moreira Xavier
1. Centro Brasileiro de Pesquisas F´ısicasRua Dr. Xavier Sigaud 150, 22290-180, Rio de Janeiro, RJ, Brazil2. Brazilian Academy of PhilosophyRua Riachuelo, 303, 20230-011, Rio de Janeiro, RJ, Brazil
Abstract
In this article it is shown that a careful analysis of Kant’s
Gedanken von der wahrenSch¨atzung der lebendigen Kr¨afte und Beurtheilung der Beweise leads to a conclusion thatdoes not match the usually accepted interpretation of Kant’s reasoning in 1747, according towhich the young Kant supposedly establishes a relationship between the tridimensionality of space and Newton’s law of universal gravitation. Indeed, it is argued that this text does notyield a satisfactory explanation of space dimensionality, actually restricting itself to justifythe tridimensionality of extension . Keywords:
Space; Physical Space; Extension; Dimensionality; Kant; Leibniz, Newton.1
Introduction
It was during the flourishing period of the mechanization of the World view, more preciselyin 1747, that Kant tried to understand why space (
Raum ) is tridimensional, in his first writ-ing titled
Gedanken von der wahren Sch¨atzung der lebendigen Kr¨afte und Beurtheilung derBeweise, deren sich Herr von Leibniz und andere Mechaniker in dieser Streitsache bedienthaben, nebst einigen vorhergehenden Betrachtungen, welche die Kraft der K¨orper ¨uberhauptbetreffen ( GSK ). The text is divided in three sections, and only the first one will be objectof study throughout this paper. It is largely accepted that the analysis carried on thatfirst section establishes a clear framework for the discussion of space dimensionality as aproblem in Physics, and represents its first physical solution. This contribution is generallysummed up in the statement that the reason for the tridimensionality of space can be foundin Newton’s law of gravitation, according to which the force between two bodies decays withthe square of the distance separating them .However, it will be seen throughout this paper that a more careful reading of
GSK leadsus to conclude – other than that is normally accepted – that Kant’s reasoning does notactually lead to a satisfactory determination of the space dimensionality , but limits itself tojustify the tridimensionality of extension ( Ausdehnung ). In any case, it can be argued thatthe original approach, conceived by Kant in his youth, strongly depends on the Newtonianconcept of force . More specifically, this means that Kant assumes force as the causa efficiens of the World changes. In this way, in this earliest text, he attempts to articulate Philosophyand Scientific knowledge trying to solve the vis viva controversy. It is in such a frameworkthat the problem of dimensionality is discussed.Although the basic idea of somehow relating dimensionality to the Gravitation law wasabandoned during the critical period of Kantian philosophy, Kant’s attempt to determinespace dimensionality from a physical law is, unquestionably, a milestone in the modern dis-cussion of this essential attribute of space. In spite of the fact that this fruitful conjecture is part of a well known and discussed text,we feel that there are still some open questions which need to be clarified, namely:– What are the bases of Kant’s conjecture?– Why does Kant ultimately limit himself, in his pre-critical phase, to explain the tridi-mensionality of extension rather than that of space ?– Did Kant’s pre-critical theories (mainly his space and time concepts) have any reper-cussion in the concepts developed by him in the critical period? In this essay, Kant’s first text is revisited, with just the scope to cast some light on aspectsraised by the first two questions above. Kant, 1747. Akademie-Ausgabe (AA): GSK, AA 01. Jammer, 1993; Brittan, 1978; Barrow, 1983; Barrow & Tipler, 1986; Caruso & Moreira Xavier, 1987. Barrow, 1983; Barrow & Tipler, 1986; Caruso & Moreira Xavier, 1987. Baker, 1935. The scenario where Kant’s
GSK was written
It is not our intention in this paper to discuss neither Kant’s broad interest on Science nor how he developed his pre-critical conception of space. However, some general remarksconcerning the philosophical and scientific frameworks where his
GSK was written are im-portant to the comprehension of his specific attempt to deduce space dimensionality fromexperience.In the plane of the history of ideas, Kant’s first published work was inserted in differ-ent important and enthusiastic debates concerning: the nature of forces; the explanationof change; and the nature of space. Ultimately, one can say that this work, as well asthe other pre-critical writings, is concerned with an examination of what Descartes, Leibnizand Newton had claimed about those points. It can be considered as a result of the hybridconfluence of critical analysis and acceptance of many of those competing claims.First of all, Kant had to discuss the nature of the motion in order to face the problem ofthe dispute between Cartesians and Leibnizians about the proper measure of force. In
GSK ,he chooses an intermediary position between the proposals of these two schools by maintain-ing that both quantities mv and mv could be conserved in different contexts. Secondly,he had to take position on the issue of the body-soul problem. At that time, among thethree possibilities – occasionalism, pre-stablished harmony and influxus physicus – he takesposition in favor to the last one. This means to admit that “if creatures can act on oneanother, all change in creation is the effect of real interaction. Perceptions are the effect ofthe body’s agency on the soul, and voluntary motion is the effect of the soul’s agency onthe body”. As will be seen in detail in the next Sections, Kant chooses Newton’s Gravi-tational force to be this agent. Last but not least, the
GSK is not imune to the famousdebate concerning the relative or absolute nature of space, which can be summarized in theLeibniz-Clarke polemics. In a nutshell, the young Kant was trying to provide a foundation for the metaphysics ofnature, understanding that its task is to discover the inner force of things, the first causes ofthe law of motion and the ultimate constituents of matter. In order to grasp the Newtonianinfluence at that point it is enough to remember what is written in the Preface of the firstedition of Newton’s
Principia : “(...) for the whole burden of philosophy seems to consistin this – from the phenomena of motions to investigate the forces of nature and then fromthese forces to demonstrate the other phenomena”. This issue is well discussed in the literature. See, for example, Britan, 1978; Falkenburg, 2000; Friedman,1998. Grillenzoni, 1998; Hoppe, 1969; Martin, 1965; Plaass, 1965; Waschkies, 1987. J.T. Baker, 1935. Garnett, 1939, pp. 89-118. Nevertheless, this question is not relevant so far as the problem of space dimensions is concerned. Laywine, 1993, pp. 25-42. For the young Kant, the inner state of the soul can be understand as a status repraesentativus universi . Laywine, ibid . And, implicitly, the Newtonian law of action and reaction. Alexander, 1956. We quote from Motte’s translation of the
Principia revised by Cajori, reprinted by University of Cal-ifornia Press, 1934. The latim text is:
Omnis enim Philosophiae difficultas in eo versari videtur, ut a
Probably under the influence of his professor Martin Knutzen, Kant developed, while at theuniversity, a special interest in Physics and Mathematics, which evolved in such a waythat his pre-critical writings essentially dealt with Physics, Cosmology and the study ofvolcanoes. Knutzen also offers to his student the Wolffian metaphysical principles and shareswith him many issues that are amalgamated in Kant’s GSK, namely: the (im)possibilityof the existence of other worlds and the body-soul problem. Implicit in those problems,as already mentioned, there are influences from Leibniz, from Descartes and from Newton. On one hand, the very title of Kant’s first work,
GKS , shows clear traces of Leibniz’s influ-ence. On the other hand, Newtonian conceptions are the gist of his argument: the previousexistence of substances – able to interact through forces – is crucial to the development ofKant’s proof, as the title of the ninth paragraph of his text about
The Living Forces ( GSK )suggests. The
Randtext found in the beginning of the ninth paragraph states his intentionto discuss the tridimensionality of space: “(...) if the substances had no force whereby theycan act outside themselves, there would be no extension, and consequently no space ”. In fact, one of the first problems Kant was concerned to was related to the corporealmatter and to the interaction of physical substances. How to express this interaction inuniversal terms of cause and effect, and in which way is matter (the substance) able toalter the state of the soul by means of the force it possess in its motion, are issues aboutwhich he reflected. Furthermore, he accepts Leibniz’ idea that the bodies have something( aliquid ) – an inherent, essential force –, prior even to extension itself: “ [In rebus corporeis]est aliquid praeter extensionem, imo extensione prius, [alibi admonuimus] .” Thus, theyoung Kant agrees with Leibniz that force precedes extension, which is indeed supposed Phaenomenis motuum investigemus vires Naturae, deinde ab his viribus demonstremus phaenomena reli-qua . Grillenzoni, 1998, pp. 23-46. Falkenburg, 2000. Remember that Knutzen has published the
Dissertatio metaphysica de aeternitate mundi impossibili (which is known was read by Kant) and, in 1735,
Commentatio philosophica de commercio mentis et corporisper influxum physicum explicando, ipsis illustrii Leibnitii principiis superstructura . Newton’s influence over Kant actually transcends the pre-critical period, in the sense that Kant tried,along all his works, to build metaphysics as science, in a way similar to the Newtonian system.
Cf.
Mathieu,1976. All English texts of Kant’s quotations are from Handyside’s translation of 1929. The reference to theoriginal text is AA 01: 23.
Randtext . “(...) wenn die Substanzen keine Kraft h¨atten außer sich zu wirken,so w¨urde keine Ausdehnung, auch kein Raum sein” . The underlining is ours. Leibniz, 1695, apud
Kant, GSK, AA 01: 17.22-23. “The very substance of things consists in the force of action and passion” ( Die philosophischen Schriftenvon G.W. Leibniz , ed. C.J. Gerhardt, Berlin, 1875-90, IV, p. 508.
4o be founded on the abstract concept of force. Since this concept is conceived by the hu-man intellect, the net Cartesian distinction between res extensa and res cogitans fades away.Let us now comment on Kant’s concept of extension. Descartes, in his
Principles , tryingto accommodate Aristotle’s thesis that, since interpenetration of dimensions is impossible,there is no space apart from bodies, identifying “space, or internal place” with the “cor-poreal substance contained in it”. In addition, Descartes claimed that “the extension inlength, width, and depth that constitutes space is evidently the same as that which consti-tutes body”. The Cartesian concepts of extension and impenetrability are essential to hismetaphysical project to reduce matter to Geometry. Leibniz, on the other hand, defendedthe view that extension was an attribute of substance . Thus, concerning the concept ofsubstance, Kant largely adhered to Leibniz’s point of view. In other words, he accepted thatextended objects occupy space not because of their extension, but by virtue of the dynamicqualities of impenetrability and resistance.There is, however, one point of disagreement with Leibniz. This is when Kant makesthe difference between vis activa e vis motrix in order to promote the triumph of influxusphysicus over the pre-stablished harmony supported by Leibniz. Concerning the nature of space, it is clear that Kant admits in the
GSK a relationalspace in a Leibnizian way, and not a Newtonian space conceived as a receptacle of bodiesand phenomena. So, let us now briefly discuss why Kant’s logical construction of the conceptof space led him to keep away from Newtonian absolute space.In all Kant’s cognitive process developed in
GSK , forces play a fundamental role. Ina certain sense, his viewpoint reminds us the stoic idea, of great impact during the lastthree centuries b.C., that there exists a force – which everything permeates –, due to theinteraction of pneuma and ponderable matter, and that this force creates a well-ordered continuum , called space .In Kant’s opinion, it is through these forces that connection ( Verbindung ) among bodiescan be established, from which the necessary order to the existence of space is achieved. This can be seen from the following passage:“
It is easily proved that there would be no space and no extension, if substanceshad no force whereby they can act outside themselves. For without a force of thiskind there is no connection, without this connection no order, and without this Apud
Des Chene, 1996, pp. 360-1. Idem . Powers, 1991. Vuillemann, 1955, p. 233. Sambursky, 1987. It is worth to notice that the young Kant contribution to the theme treated in this paper is a rupture withthe Aristotelian view of the issue – both in its general realm (the cause of the space) and in its particularaspect (the cause of dimensionality) –, through the introduction of force as the causa efficiens of space,through the concept of order . Although in a certain sense he is Aristotelic, considering the role played bythe concept of substance used in his discussion of space dimensionality, it should be stressed that, contraryto Aristotle – in whose system force ( dynamis ) leads to the rupture of cosmic order – Kant considers, in hisfirst text, force as a generator of order . rder no space.” From this quotation we clearly see that without this force ( Kraft ), from which the sub-stances are able to act externally, there would be no connection between things, no orderand therefore no space (in this sequence). Therefore, a kind of dynamical connection amongsubstances is implicit here, from which one can safely infer that Kant is denying Leibniz’sconcept of monad , since monads lack spatial extension and have no true causal relation withother monads. At this point, it is important to remember that “Leibniz only advanced tohis notion of space and time as relatives when he had redefined ultimate scientific objects asmonads”. Thus, in his first writing, Kant is giving an original justification of the relativenature of space.As Handyside well remarks in his Introduction to the English translation
Inaugural dis-sertation and the early writings on space , in this phase, “Kant considers the space as a subsidiary phenomenon , which depends on the intelligible relations of these substances”.Such relations being expressed by force laws, it seems evident to us that, although Kant al-ready accepts the core of the Newtonian scientific program, he (at least during this period)diverges from Newton in a crucial point of his system, namely the essence of space.In fact, absolute space and time are, according to Koyr´e, “(...) r´ealit´es que Newton ac-ceptait sans h´esiter – puisqu’il pouvait les appuyer sur Dieu et les fonder en Dieu ”. Butfor the young Kant, space is not the divine sensorium . On the contrary, it is an idealsubstance-dependent construction, able to express and to emphasize particularly the roleReason plays. Naturally this is not the Cartesian identification of space , quantity and corpo-real substance , for here forces cause extension . It is important to emphasize this point,since – as we shall see below – Kant’s justification of tridimensionality depends strongly on this concept of space, in opposition to the one he will adopt in his critical period.
Although Kant announces, in his first text, the intention to discuss the tridimensionality ofspace, one can argue whether it is (or not) his conception of space (in the pre-critical phase)which allowed him to lay only the basis for the tridimensionality of the extension. Indeed, inthe margin comment to the ninth paragraph, Kant states that “ the ground of the threefolddimension of space is still unknown.” and, in the Randtext of the next paragraph, hesuggests a possible relation between the tridimensionality of space and the law of attraction GSK, AA 01: 23: 05-09. “Es ist leicht zu erweisen, daß kein Raum und keine Ausdehnung sein w¨urden,wenn die Substanzen keine Kraft h¨atten, außer sich zu wirken. Denn ohne diese Kraft ist keine Verbindung,ohne diese keine Ordnung, und ohne diese endlich kein Raum.” Baker, op. cit. , p. 270. Cited as Kant’s English translation, 1929 (1979). The emphasis is ours. Koyr´e, 1971. Mamiani, 1981. This pre-critical analysis puts Man (and not God) at the center of the discussion about space and itsqualities. GSK AA 01: 23,
Randtext . “Der Grund von der dreifachen Dimension des Raumes ist noch undekannt.” It is probable that the threefold dimension of space is due to thelaw according to which the forces in the substances act upon one another.” As Handyside comment in the
Preface to his translation of part of
GSK , it seems logicalthat being space a consequence of the connection of substances,“ the special character of space as three-dimensional must, it would seem, findits explanation in the special character of law of the connections of substances.But what that is Kant declares himself unable to say (...) and in consequence hedeclares, logically enough, that space of other dimensions and other properties ispossible. ”as will be seen in the following. However, with no exception, throughout the text that fol-lows the above quotation, corresponding to the very demonstration of the statement, Kantactually refers to the dimensionality of extension .Kant’s reasoning, as seen in the previous Section, encompasses the following points: first,the idea that there exists a force inherent to the substances (that is to say, to the bodies),without which there would be no extension and no relation. Second, this force is necessaryto establish the relations among the things, necessary to the order, and finally, without thisorder, space does not exist.The fundamental role that the concept of force – the first essence of matter and of itsextension – plays in Kant’s explanatory system is corroborated by the following quotation: “Since everything which is to be found among the qualities of a thing must be ca-pable of being derived from that which contains in itself the most complete groundof the thing itself, the qualities of the extension, and subsequently their threefolddimension, will be grounded in the qualities of the force which the substancespossess in respect of the things with which they are connected.” From this quotation, independently of the subjacent force definition to be adopted (Carte-sian, Leibnizian, or Newtonian), it is clear that this is the force through which the substancesact upon one another, the one which is responsible for the collective relations which will, inKant’s view (in 1747), define space. As to the nature of this force, Kant states that “The force, whereby a substance acts in union with others, cannot be thoughtapart from a determinate law which reveals itself in the mode of its action. Sincethe character of these laws according to which a whole collection of substances(that is, a space) is measured, in other words, the dimension of extension, will GSK AA 01: 24,
Randtext . “
Es ist wahrscheinlich, daß die dreifache Abmessung des Raumes von demGesetze herr¨uhre, nach welchem die Kr¨afte der Substanzen in einander wirken.” Op. cit. , p. xi. GSK, AA 01: 24.02-09. “
Weil alles, was unter den Eigenschaften eines Dinges vorkommt, von dem-jenigen muß hergeleitet werden k¨onnen, was den vollst¨andigen Grund von dem Dinge selber in sich enth¨alt,so warden sich auch die Eingenschaften der Ausdehnung, mithin auch die dreifache Abmessung derselbenauf die Eigenschaften der Kraft gr¨unden, welche die Substanzen in Absicht auf die Dinge, mit denen sieverbunden sind, besitzen.” The underlining is ours. ikewise be due to the laws according to which the substances by means of theiressential forces seek to unite themselves”. After these considerations, Kant stresses that the law of forces to which he refers isNewton’s law of attraction which depends on the inverse of the square of the distancebetween to bodies. This choice seems to be due to the fact that Newton had shown thatthere is a principle connecting all the bodies of the Universe, which is expressed by an universal law , the Gravitational law. At this point, however, he expresses himself withdouble caution, omitting whether the tridimensionality to which he refers is related to space or to extension ( die dreifache Abmessung ) and concluding that it seems to result ( scheinetdaher zu r¨uhren ) from the form of Newton’s law of attraction, as the text below shows: “The threefold dimension seems to arise from the fact that substances in theexisting world so act upon one another that the strenght of the action holdsinversely as the square of the distances.” And then he adds:“(...) that this law is arbitrary, and that God could have chosen another, for in-stance the inverse threefold relation; and lastly, that from a different law of ex-tension with other properties and dimensions would have arisen.” after what, once again explicitly alluding to the dimension of extensions , and not to spacedimensionality ( Ausdehnungen von andern Abmessungen ), he says that“
If it is possible that there are extensions with other dimensions, it is also veryprobable that God has somewhere brought them into being; for His works have allthe magnitude and manifoldness of which they are capable. Spaces of this kind,however, cannot stand in connection with those of a quite different constitution.Accordingly such spaces would not belong to our world, but must from separateworlds. Although in what precedes I have shown that it is possible that a numberof worlds (in the metaphysical sense of the term) may exist together, in theconsiderations now before us we have, as it seems to me, the sole conditionunder which it would also be probable that a plurality of worlds actually exist. ” GSK, AA 01: 24.09-18. “
Die Kraft, womit eine Substanz in der Vereinigung mit andern wirkt, kannnicht ohne ein gewisses Gesetz gedacht werden, welches sich in der Art seiner Wirkung hervorthut. Weildie Art des Gesetzes, nach welchem die Substanzen in einander wirken, auch die Art der Vereinigung undZusammensetzung vieler derselben bestimmen muß, so wird das Gesetz, nach welchem eine ganze SammlungSubstanzen (das ist ein Raum) abgemessen wird, oder die Dimension der Ausdehnung, von den Gesetzenherr¨uhren, nach welchen die Substanzen verm¨oge ihrer wesentlichen Kr¨afte sich zu vereinigen suchen.” Margin comment to GSK, AA 01: 24.
Randtext . “
Die dreifache Abmessung scheinet daher zu r¨uhren,weil die Substanzen in der existierenden Welt so in einander w¨urken, daß die St¨arke der Wirkung sich wiedas Quadrat der Weiten umgekehrt verh¨alt.” GSK, AA 01: 24.26-30. “(...) daß dieses Gesetz willk¨urlich sei, und da Gott daf¨ur ein anderes, zumExempel des umgekehrten wirken, daß die dreifachen Verh¨altnisses, h¨atte w¨ahlen k¨onnen; daß endlich St¨arkeder viertens aus einem andern Gesetze auch eine Ausdehnung Wirkung sich von andern Eigenschaften undAbmessungen geflossen w¨are.” GSK, AA 01: 25.4-15.
Wenn es m¨oglich ist, daß es Ausdehnungen von andern Abmessungen gebe, so istes auch sehr wahrscheinlich, daß sie Gott wirklich irgendwo angebracht hat. Denn seine Werke haben alledie Gr¨oße und Mannigfaltigkeit, die sie nur fassen k¨onnen. R¨aume von dieser Art k¨onnten nun unm¨oglichmit solchen in Verbindung stehen, die von ganz anderm Wesen sind; daher w¨urden dergleichen R¨aume arbitrary character of the laws of motion.Perhaps, this led him to realize that tridimensionality of space is contingent . In addition,this also led him to speculate on the possible existence of different kinds of space and thenon the existence of multiple Worlds, which was denied by Leibniz.It must be stressed that, except for the title, in no other part of this tenth paragraphdoes Kant explicitly use the word space when referring to the tridimensionality, alluding toit only three times. The first and second, quoted above, only reinforce the idea of space defined from physical substance . The third, which also seems relevant to the theme treatedhere, is when Kant concludes his speculations by referring to space , that is, to the varioustypes of spaces, as objects of study of Geometry: “A science of all these possible kinds of space would undoubtedly be the highestenterprise which a finite understanding could undertake in the field of geome-try.” This fact can be considered as an indication of Kant’s comprehension that the study ofmore generic spaces should precede the discussion of space dimensionality in Physics. Eventhough his result refers to the dimensions of extension , Kant had to consider the possibilityof the existence of spaces with a different number of dimensions, before any formal theoryfor these types of space. It will be the Nineteenth Century discovery of non-Euclidean ge-ometries that will give impulse to the discussion of these issues. Anyhow, it seems to usthat Kant, already in 1747, foresees that the road to the comprehension of the dimension-ality of space should involve both Physics and Mathematics (through the generalization ofGeometry to higher dimensional spaces), even if he could not, at that time, envision how hisspeculations would become important to the comprehension of space tridimensionality. Inany case, he sets the basis for modern discussions of this fascinating theme.Looking forward in time, one can see that the road proposed by Kant leads to importantdevelopments. For example, one can quote the work of William Paley, which can be con-sidered the first attempt to shed light on the space dimensionality problem clearly from whatnowadays is called Anthropic arguments. In his work, Paley analyzes the consequences ofchanges in the form of Newton’s gravitational law (the inverse square law) and of the stabilityof the solar system on human existence. Starting from a theological thesis, his speculationstake into account a number of mathematical arguments which guarantee an anthropocentricdesign of the World, and rest upon the stability of the planetary orbits in our solar systemand on a Newtonian mechanical
Weltanschauung . On the other hand, in the second half of zu unserer Welt gar nicht geh¨oren, sondern eigene Welten ausmachen m¨ussen. In dem vorigen habe ichgezeigt, daß mehr Welten, im metaphysischen Verstande genommen, zusammen existiren k¨onnten; alleinhier ist zugleich die Bedingung, die, wie mir deucht, die einzige ist, weswegen es auch wahrscheinlich w¨are,daß viele Welten wirklich existiren . Garnett, op. cit. , p. 102. GSK, AA 01: 24.31-33. “
Eine Wissenschaft von allen diesen m¨oglichen Raumesarten w¨are unfehlbardie h¨ochste Geometrie, die ein endlicher Verstand unternehmen k¨onnte.” Jammer, 1993. Se also Hagar, 2008 and Kim, 2006. Whitrow, 1955. Payle, 1802. Barrow & Tipler, op. cit. Although these ideas did not resonate among the majority of the physicists andmathematicians in Riemann’s time, those questions were largely discussed by Einstein andare the fulcrum of his General Theory of Relativity.
We have seen that Kant actually proposes a justification for the tridimensionality of ex-tension and not of space , since he considers the latter as non-perceptible, as the productof an intellectual effort to seek to establish a kind of order from the intelligible things.This space appears as the object of study of Geometry and not of Physics. What reallyimpresses the soul – what is perceptible – are the spatially extended objects, the matter which causes effects on other substances : “(...) matter, by means of the force which it hasin its motion, changes that state of the soul whereby the soul represents the world to itself.” It is possible to extract intelligible relations from substances starting from causal and uni-versal laws of force like, particularly, Newton’s law, and the nature of space is dependentupon those substances. Garnett points out that Kant was arguing in circle, claiming thatthe force in bodies (or in the souls) lies in their outwardly directed acts. From the physical point of view, a deeper comprehension of Kant’s conjecture can onlybe reached by means of the field concept in Physics. It is through the solution of Laplace-Poisson equation in n -dimensional Euclidean space that the relation between the exponent ofthe Newtonian potential and the dimensionality of space is straightforwardly established. But it is only in the context of contemporary unified field theories that the problem of spacedimensionality achieves the status of a central problem in Physics: from this point of viewone can realize the full meaning of Kant’s contribution.Turning back to Kant’s first text, we cannot ignore his intention to revisit this issue andthe explicit warning at the end of the eleventh paragraph: “These thoughts may serve as an outline of an inquiry which I have in prospect.But I cannot deny that I expound them just as they have come into my mind, “Es muss also entweder das dem Raume zu Grunde liegende Wirkliche eine discrete Mannigfaltigkeitbilden, oder der Grund der Massverh¨altnisse ausserhalb, in darauf wirkenden bindenden Kr¨aften, gesuchtwarden”. Riemann, Collected Works , p. 286. See also Riemann, 1873. GSK, AA 01: 21.22-24. “(...) daher ¨andert die Materie vermittelst ihrer Kraft, die sie in der Bewegunghat, den Zustand der Seele, wodurch sie sich die Welt vorstellet.” Such a causal relation was elaborated later by ¨Uberweg, 1882, apud
Jammer, 1993. “For this to occur, a body or a soul must have a position in space. Its position in space is, however,nothing but the resultant of its outwardly directed action upon other bodies and souls, and the actions ofthe others upon it. Kant begins by using position in space as a condition of the interaction of substancesand went on to hold that such position is dependent upon the interaction”. Garnett, 1939, p. 95. Ehrenfest, 1920; Tangherlini, 1963; Caruso & Moreira Xavier, 1987. ithout that certainty which a more prolonged examination of them would havegiven. I am therefore ready to reject them, immediately a riper judment revealsto me their defects.” As far as we know – with the concordance of Brittan – there is no other attempt byKant aimed at giving a physical basis to the dimensionality issue. Indeed, afterwards Kantconsidered tridimensional space as an intuition a priori .It is known that Kant returned to this question, as certified by a manuscript included inthe Opus Postumum , but, ironically enough, there is an interruption in a key part of thetext which makes it impossible for us to discover what the mature Kant would say about theproblem of space dimensionality. We will therefore conclude this article with this reticentquotation by Kant: “The quality of space and time, for instance, that the first has 3 dimensions, andthe second only one, that the revolution is ruled by the square of the distancesare principles that (...). [interruption]” Acknowledgment
The authors are in debt to an anonymous referee for pertinent comments and usefulsuggestions.
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