An Historical Inquiry on Geometry in Relativity: Reflections on Early
Transcription
An Historical Inquiry on Geometry in Relativity: Reflections on Early
D History Research, ISSN 2159-550X December 2011, Vol. 1, No. 1, 47-60 DAVID PUBLISHING An Historical Inquiry on Geometry in Relativity: Reflections on Early Relationship Geometry-Physics (Part One) Raffaele Pisano Cirphles-École Normale Supérieure Paris, France Ferdinando Casolaro University of Sannio, Italy In order to present an historical discussion on spherical geometry in relativity between the 19th and 20th centuries, the following research is offered in two parts. Part I: Reflections on Early Relationship Geometry-Physics is an excursus focusing on the role played by geometry in history and its relationship with physics. Part II: Reflections on Late Relationship Geometry-Physics is an epistemological investigation on the historical foundations of geometry in special relativity focusing on a geometric model applied in S4 (O, x, y, z, t). In this sense, the two parts are complementary. Keywords: relationship geometry-physics-mathematics, foundations, historical epistemology of science. A Very Short Introduction on Mathematics and Geometry On Geometry and Mathematics The reasoning ascribed to mathematics originated with men who were able, in a practical way, to demonstrate the concept of one from two. They graphically described these cognitive processes by means of illustrations: e.g., one animal is less dangerous than two animals. Each culture developed its calculus related to their social typologies and demands. They used sexagesimal ratios associated with mythological and religious cults. The Egyptians obtained several results in both arithmetic and geometry: they understood the basis of multiplication and the technique of proofs. The Babylonians’ astronomy theories involved the use of primitive reasoning by ratios. They used a simple triangle having sides 3, 4 and 5. It seems that this method was used for buildings: e.g., a simple triangle, such as squadron, could be used. In order to calculate the equality between two triangles the Egyptians measured first a side of one triangle, then those of the other triangle and subsequently compared them. Moreover, by a degree of approximation, they could roughly measure a circumference, some areas’ plane figures and the volume of solids. We should emphasize that these conclusions were mostly conjecture and especially lacked the general rules applied in theory. Therefore, according to many historians, the birth of a kind of science was delayed. It was therefore more difficult for these scientific ideas to become widely accepted. Another reason however, could be related to social and cultural causes: new ideas and theories were mainly broadcast among the more affluent and educated sections of society thus denying them universal recognition. Nevertheless, the Egyptians applied this knowledge whereby geometry and the observation of phenomena married well with special building techniques around the Nile river, where all the Raffaele Pisano, Cirphles, Department of Philosophy, École Normale Supérieure Paris, France. 48 An Historical Inquiry On Geometry In Relativity: Reflections On Early Relationship Geometry-Physics (Part One) boundaries were destroyed by overflowing; for the re-building of planting lines, property ownership etc., it was necessary to use agrimensuration techniques. On the other hand, the Greeks could generalize a process of geometrical-mathematical knowledge, considering it to be merely an intellectual instrument. The Greeks did not seem as interested in the applications of geometry. They could show the equality between two triangles when only 3 data1 of each of them was known. They obtained the other three elements, which should be naturally equal by logical reasoning. Thus, geometry (Tannery, 1887; Dieudonne, 1985; Kvasz, 2006) progressed from a practical activity to an intellectual one. Reasoning and physical phenomena formed a crucial combination: discovery-propriety-relationship. Generally speaking historians of ancient science are unanimous in their claim that Pythagoras (fl. 575-490 B.C.) and Pythagoreans’ reasoning constituted an important attempt at understanding the philosophical structure of mathematics and its universe. Let us consider the discovery of musical harmonies2 in relation to mathematical ratios: Acoustical range Eighth Fifth Fourth Mathematical ratio 2:1 3:2 4:3 It is known that for Pythagoreans, a celestial body was represented by means of a range which corresponded, in a reciprocal way to harmonies of acoustical chords. Later, they also assumed valid a conjecture claiming that the motion of planets produced a sound called harmony of spheres. In effect, they discovered that harmonic ratios remained valid in both musical notes which were produced by chord perturbations, and these were produced by an air column in resonance. These aspects led them to consider the musical harmonies in the universe and the motion of bodies related to a sound. The harmony of spheres was obtained and the numbers were considered neutral. They were also able to transform a belief into early scientific theory3. Briefly, we do not focus on Greek commensurability, a (Smith, 1958) problem largely dealt with in secondary literature. In conclusion, all of these studies in geometry and mathematics contributed to producing a specific field of applicability in both mythological questions and astronomical problems. On Geometry and Astronomy During the 7th and 8th centuries (Chaldean-Babylonian period) (Youschkevitch, 1976) scholars, fascinated by the celestial bodies of the Upper Volta, attempted to closely investigate the properties of space and time in 3-dimensional geometry on spheres by means of formulas listed in tables. The constant effort to coordinate the lunar and the tropical years seems to have been one of the important stimuli in this area [astronomy and calendar] careful and continual observation of the apparent movements of the moon and the sun. This activity became “scientifically significant” at least as early as 747 B.C., the date of the first regularly repeated observations under the Assyrians. These observations were recorded in the form of tables which were apparently used by later Greek astronomers and which a great tribute to the patience and skill of Babylonian astronomers of Mesopotamia, although the length and completeness of these observations appear to have been greatly exaggerated by modern authors. Many pertinent scientific data were organized in these 1 2 3 A side was one of a given triangle. The numbers of harmonies’ ratios defines the lengths in which devices’ chords are divided. Of course, the term scientific theory does not currently stand for scientific theory. 49 An Historical Inquiry On Geometry In Relativity: Reflections On Early Relationship Geometry-Physics (Part One) tables (Clagett, 2001). Historical research into the evolution of mathematics in the past and its different fields of application reveals a remarkable interest (Sarton, 1952) both in astronomy (Neugebauer, 1945) within their society or in the astronomy–mathematics relationship. The Chaldeans, for example, went further than exploring metrics objects related to lengths, areas, volumes, systems and sexagesimal degrees. Useful as these were in practice, the Chaldeans also developed a kind of geometry, where they were able to conceive a curved space. The prediction of the first possible sighting of celestial bodies each month and its impact on society was one of the main problems (Cohen & Drabkin, 1948). In this sense, the difficulties were related to the moon and sun’s velocity, the length of daylight and the ability of the observer. Although ancient Greek knowledge of astronomy is incomplete, we can claim that the pseudo-scientific characters of the sun and moon (Kragh, 2008) were discovered. Greek scholars, supported by the previous Babylonian culture, were able to conduct studies of plane and spherical geometry. Euclidean geometry was considered useful for (ideally) describing observed phenomena. Aristotle’s reasoning was aimed at organizing an axiomatic and encyclopaedically structure of philosophical thought. The historian Hieronymus Georg Zeuthen (Zeuthen, 1902) (1839-1920) concluded that Euclidean objects existed because a constructive representation by ruler–and–compass (Mascheroni, 1797; Benjamin, 1969) was possible. Since Greek times, starting with the common belief that light travels in a straight line, many theorems were produced (especially by Euclid). They are still considered to be among the foundations of a mathematized light theory. Other studies concerned ambiguous speculations and were not commonly accepted. They were a consequence of a principle (accepted by Plato but rejected as false by modern physicists), that sight occurs through the effect of rays emanated–not by the viewed object but by the observer’s eye. In Elements, Euclid (fl. 300 B.C.) briefly wrote about the geometry of the sphere, while in Phaenomena, he dealt specifically with matters of spherical geometry. Astronomical tables were formulated based on addition and subtraction formulae. The use of the chord (modern, sin) produced substantial results. Chords and sin are essentially two equivalent functions: chord 2 sin (1) 2 Therefore, according to modern trigonometry sin is half of the chord subtended by a double angle.4 Claudius Ptolemaeus (fl. 90-168 B.C.) determined a geometrical relationship between chords-angles which he listed in tables. We highlight his argument regarding Pythagoras’ theorem in which he was able to establish a relationship:5 chord chord 180 120 (2) From (2) and by means of a simple reasoning, which is not necessary to explain, one can show that sin 2 cos 2 1 2 On this subject one should also refer to Hipparchus’s (fl. 190-120 B.C.) On the Chords in a circle. (3) Autolycus from Pitane (Heath, 1931; Neugebauer, 1975) (fl. 360-290 B.C.) wrote On the Moving Sphere (Pitane, 1971; Aujac, 1984, pp. 1-12; Pitane, 1979) and On Risings and Settings which were translated (Autolycus, 1885) in the second half of the 19th century. On the Moving Sphere is part of a booklet called Little Astronomy and was widely used by ancient astronomers. Some historians maintain that Autolycus preceded 4 5 We remark that several opinions concerning these aspects are different from one another. (Cfr: Geymonat L. 1973, I, 350-355. We also specify that equation (2) cannot be entirely correct because the units of each side are different. 50 An Historical Inquiry On Geometry In Relativity: Reflections On Early Relationship Geometry-Physics (Part One) Euclid, others claimed that his works were derived from Eudoxus6 and from Cnidus’ (fl. 408-355 B.C.) reasoning but it was generally concluded that these were the most ancient books on the matter. Greek scholars already had an interest in both plane and spherical geometry. The abundance of reasoning on spherical geometry theorems led historians to justifiably consider them to be known only by Greek scholars. Autolycus’ reasoning is surely more abstract than that of Euclid. Euclid’s style of presentation was not original. In On the Moving Sphere, Autolycus deals mainly with the meridian circles, the maximum circles and parallels. Of course, the lack of historical research in ancient times makes it difficult to propose adequate historical hypotheses. Nevertheless, one could claim that the propositions within On the Moving Sphere are arranged according to a logical order: the propositions are first shown in a general form, and then they are repeated with a clear reference to diagrams, and are proven. From an epistemological point of view, this aspect shows the Euclidean style in Phaenomena (Berggren & Thomas, 1992), in which a spherical surface is initially defined as a surface of revolution caused by a circumference around its own diameter. At that time, when geometry was applied to cosmology (Kragh, 1991) questions also arose in astronomy such as determining the time of night by observing the stars. The latter was one of the main problems in Greek astronomy. This question led astronomers to improve methods used in spherical geometry. Theodosius is quite interesting in Bitinia’s (fl. 379-395 B.C.) attempts. He collected his results in Spherica. Unfortunately, at that time it did not help to solve the Greek problem mentioned above. Menelaus (fl. 98 B.C.), in his studies on trigonometry, wrote Sphaerica collected from three books written in Arabic7 released and later translated by Francesco Maurolycus (1494-1575). In Book I, the concepts of a spherical triangle are clearly shown, e.g.: a figure composed of three arcs of the maximum circle belongs to a sphere and each of them is lesser than a semi–circle. He aimed at showing that with spherical triangles; theorems were almost similar to the ones shown by Euclid on the triangles in plane geometry. The sum of two sides of a spherical triangle is greater than the third; the sum of the angles of a triangle is greater than two right angles and equal sides subtend equal angles. Moreover, Menelaus demonstrated a singular theorem with no analogous theorems in the field of the plane triangles: if the angles of a spherical triangle are respectively equal to those of another triangle, then the two triangles are congruous. Other theorems of congruence for isosceles triangles completed the book.8 In the 2nd century Claudius Ptolomaeus (fl. 100-175 B.C.), faced with problems of spherical trigonometry, calculated the chords of the arcs, and at the same time, introduced the theoretical basis of plane trigonometry.9 Ptolomaeus dealt with spherical triangles but in his manuscripts a systematic illustration is missing and the theorems necessary to solve specific astronomical problems are the only ones to be proved. Later on, the Arabians al’Battani (fl. 858-929) and Abu’l Wafa10 (fl. 940-998), to a greater extent than Persian Nasir–Ed din (1201-1274), left their legacy of geometry and of spherical trigonometry. It seems that they were not known in Europe until the 2nd half of the 15th century, when Georg von Peuerbach (1423-1461) and his pupil Johannes Müller from Königsberg11 (called Regiomontanus: 1436-1476) began to translate Greek and Arabic works. In 6 Eudoxus studied homocentric and concentric systems. These constituted one of the main astronomical problems in antiquity. On speed explained them, but is now lost. 7 A Grecian translation had been lost. See also a new interesting approach in a recent work by Szczeciniarz (Szczeciniarz). 8 Book II is mainly on astronomy and indirectly refers to spherical geometry. Book III deals with spherical trigonometry. 9 We should emphasise that trigonometry was mainly formulated in order to be applied to astronomy and since spherical trigonometry proved more useful, it is understandable that it developed first. 10 He translated Euclid, Diophantus (fl. 284-298) and al–Khwarizmi’s (fl. 780-850) works adding his commentaries. 11 Daniel Santbech (fl. 1561) compiled a collection of De triangulis written in 1462-1463, Tabulae directionum: De triangulis planis et sphaericis libri quinque (1533) and Compositio tabularum sinum recto. An Historical Inquiry On Geometry In Relativity: Reflections On Early Relationship Geometry-Physics (Part One) 51 particular, De triangulis Spaericis collected within an organic system all the information available on spherical geometry and spherical trigonometry. Meanwhile, Johann Werner (1468-1522) improved Regiomontanus’s ideas in De triangulis Sphaericis (1514) where spherical trigonometry was emphasized due to the need for using a large amount of formulae as Regiomontanus and Werner (and later Copernicus) had used the functions of sine and cosine only. George Joachim Rhaeticus (1514-1574), a pupil of Nicolaus Copernicus (1473-1543), used all of the six trigonometric functions. Spherical trigonometry was further arranged in a system and partly developed by Francois Viète (1540-1603), who obtained all of the necessary formulae to calculate a part of a spherical rectangular triangle: two known parts and a practical rule known as Napier’s rule from John Napier (1550-1617). In the 17th century, Edmund Halley (1656-1742) used spherical geometry (also reviewed in some works). In the 18th century, thanks to Euler (1707-1783), a modern study of spherical trigonometry started to define the whole of trigonometry by main principles. Carl Friedrich Gauss (1777-1855), who considered a curved surface a space by itself, provided a generalization of spherical trigonometry. In a later period all of the studies mentioned produced a generalization of geometry on curved surfaces which became known as non–Euclidean geometries. In order to have a global view of scientific works12 contested in the 19th century we present an incomplete excursus of the most relevant contributions to geometry and mathematics in that short revolutionary period. Table 1 A partial excursus on geometry and physics–mathematics manuscripts Year 1799 1799 1805 1820 1821 1822 1823 1826 1827 1829(30) 1829 1831 1832 1833 1835(38) 12 13 Author and manuscript Theory C.F. Gauss (177-1855): Demonstratio nova theorematis omnem functionem algebraicam Geometry rationalem integram unius variabilis in factores reales primi vel secundi gradus resolvi posse. G. Monge (1746-1818): Traité de Géométrie descriptive Geometry P. S. Laplace (1749-1827): Traité de Mécanique céleste Physics–mathematics J.B.J. Fourier (1768-1830): Mémoire d'analyse sur le mouvement de la chaleur dans les Physics–mathematics fluides A. L. Cauchy (1789-1857): Cours d'analyse de l‘École Polytechnique Mathematics J. V. Poncelet (1788-1867): Traité des propriétés projectives des figures. Geometry A. L. Cauchy (1789-1857): Résumé des leçons sur le calcul différentiel Mathematics N.I. Lobacevskij13 (1793-1856): Exposition succincte des principes de la géométrie, avec Geometry une démonstration rigoureuse de la Théorie des Paralléles C. F. Gauss (177-1855): Disquisitiones generales circa superfice curvas Geometry N.I Lobacevskij (1793-1856): “O Nachalakh Geometrii” in Kazanskij Vestnik Geometry A. L. Cauchy (1789-1857): Leçons sur le calcul différentiel Mathematics E. Galois (1811-1832): Deux mémoires d’analyse in Azra J. P., Bourgne R. Mathematics(-geometry) Gauthier–Villars, 1862, Paris. J. Bolyai (1802-1860): “Appendix” in scientiam spatii absolute Veram exhibens: a veritate aut iaisitate Axiomatis XI Euctidei (a priori haud unquam decidcnda) independentem;adjeeta,ad casum faisitatis, quadratura circuti geometrica. Auctore Geometry Johanne Bolyai de Bolya, Geometrarum in Exercïtu Caesareo Regio Austriaco Castrensium Capitaneo. Maros-Vasarhelyini. J. Bolyai (1802-1860): Tentamen iuventutem studiosam in elementa matheseos puræ elementaris ac sublimioris methodo intuitiva evidentiaque huic propria introducendi: cum Geometry appendice triplic. Auctore Professare Mathescos et Physices Chemiaeque publico ordinario. Toums Primus, umptibus Academiæ scientiarum hungaricæ. N.I Lobacevskij (1793-1856): Novye nacala geometrij s polnoj teoriej parallel'nyh Geometry Pisano & Capecchi, 2009, 83-90. For the history of geometries: Boris & Rosenfeld, 1998. 52 1836 1836 1837 1840 1868 1878 1885 1887 An Historical Inquiry On Geometry In Relativity: Reflections On Early Relationship Geometry-Physics (Part One) P. S. Laplace (1749-1827): Exposition du système du monde Physics–mathematics N. I. Lobacevskij (1793-1856): “Primeniene voobrazaemoj geometrii k nekotorym Geometry integrlam”, in Kazanskij Vestnik N.I Lobacevskij (1793-1856): “Géométrie imaginaire” in Journal für die reine und Geometry angewandte Mathematik, XVII. N. I. Lobacevskij (1793-1856): Geometrische Untersuchungen zur Theorie der Geometry Parallellinien N. I. Lobacevskij (1793-1856): La Science Absolue de l’Espace indépendante de vérité ou Geometry de la fausseté de l’Axiome XI d’Euclide (que l'on ne pourra jamais établir a priori) J. B. J. Fourier (1768-1830): Analytical theory of heat Physics–mathematics Autolycus from Pitane. (fl. 360-290). De sphaera quae movetur liber de ortibus et Geometry occasibus libri duo, transl. by. Hultsch, Teubneri, Lipsiae. J. H. Poincaré, “Sur les hypothèses fondamentales de la géométrie” in Bulletin de la Geometry Société Mathématique de France, XV Although the chronology is not very detailed, as in Table 1 above, basically, there is enough evidence to suggest the significant role and influence played by geometry and mathematics in future physics: physics-mathematics or rational theory. On Geometry and Mathematics Applied to Mechanics It is likely that the Greeks would have been the first to attempt to solve some problems of representation and it is not improbable that in the classical age a system of representation similar to the one developed during the Renaissance had already been developed. There is, however, no evidence that a mathematical and unique definition of space can be found in the pre-historical representations. At the beginning of the Renaissance, architects (Briggs, 1927; Pisano, 2009; Pisano & Gaudiello, 2009) were interested in re-evaluating14 De architettura (Vitruvius, 1990) by Vitruvius (fl. 80 (70?)-23 B.C.). The application of geometry to early mechanics became the first guide15 for both design (practical) (Casolaro, 2004) and building. Its translation also included figures by Daniele Barbaro (1513-1570) published in Venice in 1567 and it made an important contribution to the popularization of Roman works (Reymond, 1927) during the Renaissance. Figure 1. Tower section–Book I16 14 De architectura was probably written between 27 and 23 B.C. In 1414, the manuscript was re-translated by Poggio Bracciolini (1380-1459), historian and Italian humanist. In regard to the originality of the manuscript, George Sarton (1884-1956) and John Louis Emil Dreyer (1852-1926) thought that De architectura could also be post and written by a “pseudo-Vitruvius”. (Cfr.: Stahl, 1972, 123). 15 It seems that Theophrastus (fl. 372-287 B.C.) was also a guide for the architects at that time. 16 Vitruvius, 1567. I dieci libri dell'architettura, by Daniele Barbaro, Libro I, cap.V, 49. (The two images present the importance of geometry both as pure discipline and applied to architecture). On the history of science and architecture, please see recently: Capecchi & Pisano, 2010. 53 An Historical Inquiry On Geometry In Relativity: Reflections On Early Relationship Geometry-Physics (Part One) Figure 2. Plant and wall–Book I17 In particular, if we refer to mechanics (Clagett, 1959), and more specifically to geometry in statics (Capecchi & Pisano, 2007), we will notice many Renaissance building problems (Pisano, 2008) already discussed in De architectura. For example, Vitruvius’ reasoning on Gerone II’s (fl. 308-216. A.C.) golden crown and Book IX completed by Archimedes (fl. 287-212) are very well–known. De architectura consists of ten Books which correspond with the reasoning put forward by Heron from Alexandria (fl. I B.C.? II A.C.?). Without a doubt, Vitruvius would also have been familiar with the theories of Marcus Terentius Varro Lucullus (fl. 116-27 B.C.) as found in Disciplinarum. In Book I, Vitruvius suggested (sometimes ambiguously) that both mathematical and geometrical knowledge were necessary for architects and builders and applied geometry was useful in astronomy (Book IX). The 12th century brought dramatic changes in style and in Gothic architecture. One of the main problems was to achieve maximum light and space by minimizing the least clutter of walls and structures. Generally speaking, one of the first physical sciences to be influenced by mathematics was René Descartes’18 (1625-1637) Optics in which any physical law was followed by a mathematical interpretation. The methods of perspective, in geometry, can be considered to be among those used to represent figures of space on a plane. Gothic architecture lengthened vertical lines and increased the geometric complexity of the plants producing more aisles. Thus, Gothic with radial chapels, perspectives continually changing, according to the dynamic and ever changing interplay of light, often filtered through the coloured stained glass. Therefore, the Gothic cathedral around which generations of builders and craftsmen flourished is in fact an extremely logical and stable building. The representation of the technical details of a figure is achieved through the methods of descriptive geometry (Monge, 1811), while projective geometry (Poncelet, 1865-1866) serves to produce a representation through a transformation caused by the use of projections and sections. An Epistemological Excursus on Astronomy The history of astronomy (as cited in Dumas, 1957; as cited in Taton, 1961, pp. 123-126), (including cosmology) was born at least two thousand five hundred years ago (Duhem, 1958): Comparing such a long 17 Vitruvius, 1567, Libro I, V, 52. Descartes, 1897-1913. See Discours de la méthode et Essais, Specimina philosophiae Vol. VI; Physico–mathematica Vol. X, Le Monde ou Traité de la lumière, Vol. XI (Id. 1964-1974). 18 An Historical Inquiry On Geometry In Relativity: Reflections On Early Relationship Geometry-Physics (Part One) 54 period with nearly four centuries of physics, from the Renaissance until today, seems odd. The history of astronomy seems much older than the history of physics. Nonetheless, at least with the work of Alexandre Koyré (Koyrè, 1957) (1892-1864) and Thomas Kuhn (Kuhn, 1962, 1978) (1922-1996), it has been transformed from a descriptive history (results, devices, scientists and institutions) to an interpretative one. This transformation did not occur in the history of astronomy, although it had been initiated during the Copernicus revolution which was extremely important both from an intellectual and also foundational point of view. This historical deficiency may depend on many different factors, one being a history too strictly tied to the division between two cosmological theories, so confining the interpretative data to just a few hypotheses. Yet in the history of astronomy a further historiographical problem exists, that is the question of the temporal aspect: Table 2 A temporal excursus for the history of astronomy (adapted by Drago, 1991) Items Astronomy Pre–Hellenism Clergies Objects Cosmos, Sun and Stars Theories Trigonometry Type of Knowledge of science Isolated and non–systematic Hellenism 1540 1687 1820 Copernicus, Ptolomaeus Newton Laplace Kepler, Galilei Cosmos, Sun and Sun, Earth and Solar Sun, Earth and Solar Solar system and Stars system system Galaxies Trigonometry, Trigonometry, Infinitesimal Infinitesimal geometry geometry analysis analysis, mechanics The only science for A new science for a A physical theory to a (mathematical) general interpret terrestrial A mathematicaldescription of nature understanding of the and celestial pattern theory (cosmos) World phenomena It is worth noticing that, according to the previous Table 1, the ancient history of astronomy cannot be fully examined, due to its insufficient theorization, since it is largely rooted in the cultural geographical and temporal context. As a matter of fact, its interpretation mainly depends on its social and cultural background. Subsequently, using a uniquely conservative approach (religious), the next step was the study (laically) of the universe. That is why this period seems, from a temporal point of view, very short. Only two millennia later did astronomers reconsider the conjecture of a cosmological view founded on a curve basis and only when it was necessary to face the problem of determining the most suitable geometry for the space ruling laws. The scientific research at that time seems to echo (or be centered around) the scientific programmes in Traité de Mécanique céleste and Exposition du système du monde (Laplace, 1836). Both are the crucial programmes proposed by Pierre Simon Laplace (Gillispie, 1997) (1749-1827) and are focused on central forces offering the 2 possibility of realizing differential equations d x f ( r , v, t ) by as an exponent different even from 2. dt Man being induced, by the illusions of his senses, to consider himself as the centre of the universe, it was easy to persuade him, that the stars influenced the events of his life, and could prognosticate to him his future destiny.19 Simeon-Denis Poisson (1781-1840), fully respecting the Newtonian paradigm (Newton I., 1730)20 in his interpretation of all types of celestial and earthly phenomena through cause–forces, that is, typically, the central forces, applied the scheme to many other cases, in particular to heat phenomena (Lavoisier & Laplace, 1784), 19 Laplace 1809, 248-249, line 23. (In French: “L’homme, porté par les illusions des sens à se regarder comme le centre de l'univers, se persuade facilement que les astres influent sur sa destinée, et qu'il est possible de la prévoir par l'observation de leurs aspects au moment de la naissance.” (Laplace 1836, Tome II, 373, line 3). 20 Please, see the Newtonian claim on last queries in: Newton I. 1730, 388-389. An Historical Inquiry On Geometry In Relativity: Reflections On Early Relationship Geometry-Physics (Part One) 55 discovering some laws of gases, e.g., the law of adiabatics (Poisson, 1823). Table 3 Main Newtonian paradigm Items in theory Space Time Basic concepts Inertia Atom Fluid Mass Interaction Newtonian Mechanics (1687) Absolute and mathematical. Absolute and mathematical. Accelerations. Perpetual. Infinitesimal part of matter. Phlogiston (corporeal) Inertial. Force–cause. Problem of the theory F ma Arguing techniques Solutions Differential equations. Any possible solution, for a given force. Charles Singer (1876-1960) (Singer, 1959), referring to the Newtonian paradigm and the development of astronomy, proposed the following classification: (a) Experimental astronomy: observation of celestial bodies by telescope (b) Dynamical astronomy: Laplacian program (c) Astrophysics: physical and chemical studies of celestial bodies. With regard to astronomy, theories which were included in mechanics became rational ones, that is to say, a physical-mathematical (Paty, 2001; Paty, 1994) theory in which, in some cases, the physical principles (and experimental phenomena) could also be considered. These aspects developed mainly due to Jean Baptiste Joseph Fourier (Grattan-Guinness & Ravetz, 1972; as cited in Gillispie & American Council of Learned Societies, 1970-1990) (1768-1830) who included numerous mathematical calculations resulting in the theory appearing to be a completely mathematical one: Théorie analytique de la chaleur (Fourier, 1822). Let us examine some historical examples which occurred in the 19th century. Table 4 Examples of the roles played by mechanics in the theory (adapted by Drago, 1991) Celeste Planetary MECHANICS (Mathematics) Engineering Corporeal Molecular Stars, comets, planets satellites, Stability of planetarium system Geodesy, cartography Mechanics, instruments, frictions, structures, analytical theory of heat Statics, dynamics, hydrodynamics, crystallography Elasticity In 181121, on the occasion of a competition, whose subject was the propagation of heat in solid bodies, Fourier improved his work, presented again in Mémoire su la théorie analytique de la chaleur (Fourier, 1829). In 21 On 21 December 1807, he presented his work on heat, Théorie de la propagation de la chaleur dans les solides, (Fourier, 1807. Tome I, 112-116. (n. 6, mars 1808); Id., 1888-1890.Œuvres de Fourier) at the Académie des Sciences de Paris. He focused on heat transmission between discrete masses and special case-studies of continuous bodies (e.g. ring, sphere, cylinder, rectangular prism and cube). The prize was conferred only in 1812. 56 An Historical Inquiry On Geometry In Relativity: Reflections On Early Relationship Geometry-Physics (Part One) 1822 Fourier (Grattan-Guinness 1970-1990; as cited in Gillispie & American Council of Learned Societies, 1970-1990) published a monographic work, the Théorie analytique de la chaleur (Fourier, 1822) which contained (in its first part) the whole of his Mémoire of 1811. The basic proprieties claimed by Fourier concern the capacity of bodies to absorb and transfer heat. However, a small group of primeval facts deduct the principles of the theory. As a matter of fact, one can see this aspect in rational mechanics, where Fourier claimed that The principles of the theory are derived, as are those of rational mechanics, from a very small number of primary facts, the causes of which are not considered by geometers, but which they admit as the results of common observations confirmed by all experiment. The differential equations of the propagation of heat express the most general conditions, and reduce the physical questions to problems of pure analysis, and this is the proper object of theory. They are not less rigorously established than the general equations of equilibrium and motion. 22 For his Habilitationsschrift (probationary essay), Bernhard Riemann (1826-1866) (Freudenthal, 1970-1980) studied Fouriers’ series and presented the essay in 1853. Although trigonometric series were long used in astronomy, Fourier made frequent use of them in solving the heat equation but did little to resolve the fundamental issues. Riemann’s essay made considerable progress towards solving this problem, first by giving a criterion for a function to be integrable and then by obtaining a necessary condition for a Riemann integrable function to be representable by Fourier’s series. Nevertheless, at that time, Fourier’s analytic theory of heat was too under-developed to be included in a definitive mathematical (-mechanical) scheme (Grattan-Guinness, 1969), in fact, “part of its impact was that it did not fit into the scheme of rational and celestial mechanics”23. Fourier based his scientific thought firmly on the role played by mathematics with regard to physical phenomena, which guided his thinking towards a rational physics. Many physical concepts (e.g., velocity, propagation) were supported by means of differential equations and integral calculus. This mathematical aspect gave these concepts rationality thereby producing a physical-mathematical theory. Therefore it can be concluded that a theoretical physics theory becomes more significant when it is included in a larger and consolidated theory and strongly interpreted by mathematics. Following Fourier’s approach, in 1861 Gabriel Lamé (1795-1870) wrote Leçons sur la théorie analytique de la chaleur (Lamé, 1861), focusing on the mathematical role to be played in the transmission of heat, independently, both of physical law phenomena and the nature of heat. Like Fourier (Pisano & Capecchi, 2009), Lame was not interested in experiments and measuring procedures, hypotheses on the nature of heat, the physical theory of heat, or specific heat, as one can read in his theoretical premise in his Discours préliminaire24 where he establishes that his course on the analytical theory of heat does not presuppose the laws of heat-exchange, or radiation. 22 Fourier 1878, 6, line 11. (In French: “Les principes de cette théorie sont déduits, comme ceux de la mécanique rationnelle, d'un très–petit nombre de faits primordiaux, dont les géomètres ne considèrent point la cause, mais qu'ils admettent comme résultant des observations communes et confirmés par toutes les expériences. Les équations différentielles de la propagation de la chaleur expriment les conditions les plus générales, et ramènent les questions physiques à des problèmes d'analyse pure, ce qui est proprement l'objet de la théorie. Elles ne sont pas moins rigoureusement démontrées que les équations générales de l'équilibre et du movement.” (Fourier 1822, xj, line 4). 23 Keston D. “Joseph Fourier, Politician & Scientist”, http://www.todayinsci.com/F/Fourier_JBJ/FourierPoliticianScientistBio.htm (Quotations marks from the author). 24 “Le Cours que j’entreprends aujourd’hui a pour objet principal d’établir la Théorie analytique de la Chaleur, sans partir d’aucun principe hypothétique relatif à la constitution intérieure des milieux solides, sans présupposer les lois de l’échange calorifique, ou du rayonnement particulaire, sans adopter aucune restriction pour les variations de la conductibilité autour d’un même point. Je suis de plus en convaincu qu’en évitant, de cette manière, toute idée préconçue sur les lois naturelles, […]. En effet, la Théorie de l’Élasticité, complètement dégagée de tout principe hypothétique, peut démontrer rigoureusement, en s’appuyant sur les faits, que dans les milieux diaphanes, les particuliers pondérables vibrent lumineusement” (Lamé, 1861. V). An Historical Inquiry On Geometry In Relativity: Reflections On Early Relationship Geometry-Physics (Part One) 57 Table 5 Basic concepts in Fourier’s theory Items in theory Space Time Basic concepts Heat Problem of the theory Arguing techniques Solutions Fourier’s Théorie analytique de la chaleur (1822) Mathematical for calculus. Mathematical for calculus. Temperature as a mathematical and continuous function. Velocity of heat transmission. Declared doubts on the nature of heat overcame by trust in mathematics laws25. To calculate the temperature T= f(x,y,z,t) for an isotropic and homogènes solid bodies–system which expresses the value of v (Fourier, 1822). Differential calculus and Integral calculus. Differential equations applied to particular case-study and integral calculus applied to general cases to obtain (only) mathematical results. Series expansions. Ultimately, the recognition of the importance of mathematics in a theory occurs when it is included in a new theory: e.g., propagation, velocity etc. mathematically applied to physics. The theory was promoted by means of an advanced mathematics (differential calculus by partial derivates, integral calculus, series, etc.) to interpret each field of phenomena. In this sense, a theory is absorbed by mathematics, producing crucial consequences: that is the birth of new theories, e.g., Théorie analytique de la chaleur, mécanique céleste and Exposition du système du monde (Laplace, 1805, 1836). Nevertheless, there is the risk that the original theory can become devalued (Pisano & Capecchi, 2009). Some Final Remarks Greek geometry as a proved science is essentially considered from 500 to 300 B.C. (Archimedean era). One has to wait for a more thorough application of geometry to machines (Knobloch, 2004). We do not have to wait until medieval or early modern times for the application of geometry to the investigation of nature, for it began in both physics and astronomy in the fourth century and matured in the Hellenistic and Greek–Roman periods (Clagett, 2001). Thus, even if it is not formalized and is incomplete, the Greek astronomers already had enough knowledge to apply plane and spherical geometry in the interpretation of natural phenomena and astronomy, e.g., for the motions of the moon and sun. Let us consider the Chaldean–Babylonian era. This part of the history of science is fragmented with regard to philosophical and device studies. This science in antiquity had above all crucial theoretical significance. It was oriented towards astronomy, geography and mathematics. In fact, practical studies, useful to astronomers and geographers (tables, formulas etc.) were formulated. Nevertheless, an intrinsic improvement in spherical theoretical geometry, e.g., by Autolycus and Menelaus, was developed. Let us also recall the spherical triangles theory developed at the same time as the plane theory (Elements, Book I). Theodosius also disputed spherics theorems, even if he presented them like theorems on solids. A collection of interesting results on spherical geometry was developed up to the time of Ptolomaeus who gave us one of the first trigonometric rules for finding the chord as the sum of two angles. Since the 1950s, all of these studies have not always been historically recorded as scientific ones by historians. On this point Clagett claimed: 25 “15. Il restait encore à comparer les faits avec la Théorie. […]. Ces expériences confirment le principe dont on est parti, et qui est adopté de tous les physiciens, malgré la diversité de leurs hypothèses sur la nature de la chaleur. (Fourier, 1822. 12, line 16). “Section II. […] 22. On ne pourrait former que des hypothèses incertaines sur la nature de la chaleur, mais la connaissance de lois mathématique auxquelles ses effets sont assujettis est Independent da toute hypothèse; elle exige seulement l’examen attentif des faits principaux que les observations communes ont indiquées, […]” (Fourier, 1822, 18, line 7). 58 An Historical Inquiry On Geometry In Relativity: Reflections On Early Relationship Geometry-Physics (Part One) One of my colleagues has raised a question as to whether the title [of the book:] Greek Science in Antiquity is a tautology. My answer is no for two important reasons. [1] In the first place there is other than Greek Science in antiquity (e.g., Babylonian Science or Indian Science). [2] Secondly and more important, I have stressed throughout the volume that the Greek scientific corpus has had a long life in antiquity, in the Middle Ages, and in early modern times (Clagett, 2001). 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