PMI Ciência: Mitos, Histórias e Factos Arquímedes

Referência: http://www.aip.org/pt/june00/origins.htm

The Origins of Mathematical Physics: New Light on an Old Question

A recently resurfaced tenth century manuscript, the Archimedes Palimpsest, includes the sole extant copy of Archimedes’s treatise, the Method. As scholars begin study, new insights into Archimedes are emerging. -- Reviel Netz

Imagine that you have to start science from scratch. … the Archimedes manuscript has been overwritten Upon what disciplines should you draw? Philosophy, by a twelfth century prayer book. (Palimpsestos is the for instance, discusses the nature of time, space, and Greek word for rescraped, or overwritten, parchment.) reality. Religion, too, tries to make sense of the world Work is only just beginning on uncovering and as a whole; and so, sometimes, does literature. Several studying the original text. Many scholars in the field disciplines—for example, biology and medicine—deal hope we are near a much better understanding of with special and highly significant features of the Archimedes. I have looked at the palimpsest, and I world. Such are the most natural ways to begin believe this hope is well founded. In this article, I thinking about the world, and, in fact, most cultures delineate some of Archimedes’s originality, give an make sense of their world through a combination of example of the new information the Archimedes such intellectual resources. Mathematics, in Palimpsest may provide us, and I suggest, tentatively, comparison, appears like a non-starter. Here is a theory what Archimedes’s mathematical physics may have dealing with abstract objects, aiming at internal meant. coherence rather than at connection to any external Archimedes’s originality reality. All cultures develop some ways of dealing with “Give me a place to stand, and I shall move the calculation and measurement, and in some societies, a Earth”—Archimedes may indeed have said this: more abstract discipline, a “mathematics,” may also Among the wealth of anecdotes and legends emerge. But it is a peculiarity of the modern world to surrounding the man, this is perhaps one of the more take this abstract discipline as the cornerstone for plausible.1 He was referring to the law of the lever, science. which (in the variant form of the law of the balance) he In this respect, as in many others, modern science is had proved in his treatise, Planes in Equilibrium. One Greek: The strange combination of mathematics and can say that Archimedes moved the Earth—in physics is a Greek invention, pioneered by principle—without standing anywhere: Pure thought Archimedes. Modern science is a mythical monster: alone showed how the Earth must behave. half-goat, half-bird. The student of physics is led Ernst Mach, who in the beginning of this century simultaneously to the laboratory, to face the offered a philosophy of science in which science was phenomena of physical reality; and to the math course, assumed to do no more than arrange sensory input, to forget about the phenomena and to contemplate pure thought Archimedes’s proof of the law of the lever was abstractions. That this hybrid existence is at all fertile flawed. Effectively—so Mach argued—Archimedes is amazing: We use it, because we have discovered its had reasoned in a circle, taking for granted his main effectiveness through experience. result. Otherwise, how could he obtain a physical result But just what went through the head of the person who without any experiment? However, Mach failed to see first tried to put this combination to work? Why marry the way Archimedes’s proof worked: No circular the goat to the bird in the first place? In Syracuse, reasoning was involved.1 The way in which Sicily, in the third century BC, Archimedes set out in a Archimedes manages to have satisfactory physical series of works to combine physics and mathematics. proofs, based purely on conceptual considerations, may How did he manage to do it? And why did he believe it be neatly illustrated by a closely related proof, found in was worth the try? Planes in Equilibrium and presented in box 1: that the In October 1998, a manuscript containing some of center of the weight of a triangle lies at the intersection Archimedes’s works, known to scholars as the of its medians. (The modern term “center of gravity” Archimedes Palimpsest, resurfaced from long should be avoided for Archimedes, as it misrepresents obscurity and was sold in New York for two million both his language and his underlying thought.) dollars. The private owner has, with great generosity, This proof is one of the earliest and most simple agreed to make it available for research and applications of mathematics to physics. Archimedes publication. This manuscript, shown in figure 1 and on went on to a backward application: using such physical this month’s cover, is a unique source of evidence for results to derive results in pure mathematics. Archimedes’s thought. Among its many treasures is the Archimedes died in 212 BC, but what may be his most only evidence we have for the treatise known as the interesting work—the Method—came to the attention Method, in which physics and mathematics are most of modern readers only in 1906 AD, following the intimately combined by Archimedes. initial discovery of the Archimedes Palimpsest. The treatise is surely one of the longest-neglected pieces of

A. Serralheiro 1 Academia Militar, Outubro 2004 PMI Ciência: Mitos, Histórias e Factos Arquímedes intellectual legacy in the history of science. It is allows him to use physics—in particular, mechanics— fascinating to speculate how the history of science to derive mathematical results. Archimedes derives a might have looked with Galileo, say, aware of its wide range of results, including such highlights of his existence. For it is in this work that Archimedes most mathematical achievement as the volume of the sphere explicitly connects the mathematical and the physical. and the volumes of segments of solids of revolution. He claims here that he has invented a procedure that … The Eurekas of Archimedes Archimedes made many discoveries. Some, perhaps most, he committed to writing, and some of these writings, perhaps most, survived. The most remarkable of them, the Method, survives only thanks to the Archimedes Palimpsest. The palimpsest contains, in more or less fragmentary form, seven works by Archimedes. The first three form a natural sequence in mathematical physics: • Planes in Equilibrium. Archimedes proves the law of the balance and derives results for centers of gravity in planes. • On Floating Bodies. Here he proves his law of buoyancy and derives results for the flotation of solids of geometrically interesting shapes. • Method. As illustrated in the main text, the law of the balance is used to derive geometrical properties. Next come four studies in pure geometry: • Spiral Lines. Spirals are first defined and their lengths and areas are measured. • On Sphere and Cylinder. Archimedes provides the ratios for the surface area and volume of a sphere and then solves a series of problems concerning spheres. • Measurement of the Circle. An approximation of the value of p is obtained using a method that can, in principle, be extended indefinitely. • Stomachion. Only a fragment survives. Apparently, this is a study in a tangram-like game, where areas are covered by given geometrical figures. Three further works of Archimedes have survived in Greek in other manuscripts: • Quadrature of the Parabola. Related in certain ways to the Method, this is an exploration of the applicability of the law of the balance to geometry. • Sand-Reckoner. In this complex miscellany, Archimedes sets out to measure how many grains of sand it would take to fill up the universe, in the process contributing to astronomy as well as to calculation techniques. • Conoids and Spheroids. Archimedes introduces the solids of revolution of conic sections, and provides several measurements for those figures. Archimedes may also have been the author of the Cattle Problem, a numerical problem comparable in spirit to the Sand-Reckoner, although the attribution is nowhere directly founded. An Arabic text, On Lemmas, showing various configurations of circles and measurements concerning them, may be derived from Archimedes; the same may be said, with even less confidence, of an Arabic treatise on the Construction of the Regular Heptagon. We know for sure, on the authority of the knowledgeable commentator Pappus, that Archimedes had produced a work (now lost) on Semi- Regular Solids (the faces of which are all regular, though not identical). One may go on counting, beyond these 14 works, well into the realm of myth, as recounted by Greek and Arabic stories on Archimedean feats of engineering and proof. We cannot know how much the Archimedean corpus originally contained. However, we do have a relatively large body of surviving works—more representative, probably, than for any other mathematician from antiquity: None of the others appears to us with as well-defined a scientific personality. … References 1. An excellent source for information on Archimedes, including evidence for and against the anecdotes and legends, is E. J. Dijksterhuis, Archimedes, Princeton U. P. (1987). 2. J. L. Heiberg, Archimedis Opera (2nd ed.), Teubner, Leipzig (1910–1915). 3. See G. E. R. Lloyd, Demystifying Mentalities, Cambridge U. P. (1991), and R. Netz, The Shaping of Deduction in Greek Mathematics, Cambridge U. P. (1999). 4. The history of the Archimedes Palimpsest, as well as biographical information about Archimedes, can be found at the website of the Walters Art Gallery.

Reviel Netz is an assistant professor of classics at Stanford University in Palo Alto, California. He is currently preparing a translation, with commentary, of the works of Archimedes and is part of the international team restoring and editing the Archimedes Palimpsest. © 2000 American Institute of Physics

A. Serralheiro 2 Academia Militar, Outubro 2004