هندسة مطلقة
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| التاريخ (خط زمني) |
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الهندسة المطلقة إنگليزية: Absolute geometry هي الهندسة الرياضية المبنية على النظام البديهي الذي لا يفترض مسلمة التوازي أو أي من بدائلها. تم استخدام هذا المصطلح من قبل العالم يانوس بولياي في العام 1832.[1][2] ويطلق عليها أحياناً اسم الهندسة الحيادية neutral geometry[3] حيث أنها حيادية تجاه مسلمة التوازي.
وعليه فإن نظرياتها تكون صحيحة في الهندسة اللاإقليدية بالإضافة إلى الهندسة الإقليدية. في العناصر الإقليدية تتجنب الافتراضات الـ28 الأولى استخدام مسلمة التوازي، وبالتالي يمكن تطبيقها على الهندسة المطلقة. The first four of Euclid's postulates are now considered insufficient as a basis of Euclidean geometry, so other systems (such as Hilbert's axioms without the parallel axiom) are used instead.[4]
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الخصائص
In Euclid's Elements, the first 28 Propositions and Proposition 31 avoid using the parallel postulate, and therefore are valid in absolute geometry. One can also prove in absolute geometry the exterior angle theorem (an exterior angle of a triangle is larger than either of the remote angles), as well as the Saccheri–Legendre theorem, which states that the sum of the measures of the angles in a triangle has at most 180°.[5]
Proposition 31 is the construction of a parallel line to a given line through a point not on the given line.[6] As the proof only requires the use of Proposition 27 (the Alternate Interior Angle Theorem), it is a valid construction in absolute geometry. More precisely, given any line l and any point P not on l, there is at least one line through P which is parallel to l. This can be proved using a familiar construction: given a line l and a point P not on l, drop the perpendicular m from P to l, then erect a perpendicular n to m through P. By the alternate interior angle theorem, l is parallel to n. (The alternate interior angle theorem states that if lines a and b are cut by a transversal t such that there is a pair of congruent alternate interior angles, then a and b are parallel.) The foregoing construction, and the alternate interior angle theorem, do not depend on the parallel postulate and are therefore valid in absolute geometry.[7]
In absolute geometry, it is also provable that two lines perpendicular to the same line cannot intersect[8] (which makes the two lines parallel by definition of parallel lines), proving that the summit angles of a Saccheri quadrilateral cannot be obtuse, and that spherical geometry is not an absolute geometry.
العلاقة بالهندسات الأخرى
The theorems of absolute geometry hold in hyperbolic geometry, which is a non-Euclidean geometry, as well as in Euclidean geometry.[9]
Absolute geometry is inconsistent with elliptic geometry: in that theory, there are no parallel lines at all, but it is a theorem of absolute geometry that parallel lines do exist. However, it is possible to modify the axiom system so that absolute geometry, as defined by the modified system, will include spherical and elliptic geometries, that have no parallel lines.[10]
Absolute geometry is an extension of ordered geometry, and thus, all theorems in ordered geometry hold in absolute geometry. The converse is not true. Absolute geometry assumes the first four of Euclid's Axioms (or their equivalents), to be contrasted with affine geometry, which does not assume Euclid's third and fourth axioms. (3: "To describe a circle with any centre and distance radius.", 4: "That all right angles are equal to one another." ) Ordered geometry is a common foundation of both absolute and affine geometry.[11]
The geometry of special relativity has been developed starting with nine axioms and eleven propositions of absolute geometry.[12][13] The authors Edwin B. Wilson and Gilbert N. Lewis then proceed beyond absolute geometry when they introduce hyperbolic rotation as the transformation relating two frames of reference.
مستويات هيلبرت
A plane that satisfies Hilbert's Incidence, Betweenness and Congruence axioms is called a Hilbert plane.[14] Hilbert planes are models of absolute geometry.[15]
عدم الاكتمال
الهندسة المطلقة هي مثال على عدم الاكتمال لنظام بديهي. على سبيل المثال خذ العبارة التالية (إن مجموع قياسات زوايا أي مثلث يساوي إلى مجموع قياسي زاويتين قائمتين). هذه العبارة لا يمكن برهانها في الهندسة المطلقة. فإذا كانت العبارة مبرهنة فإنها ستكون صحيحة في هندسة القطع الناقص، حيث أن مجموع قياسات زوايا أي مثلث هو أقل من مجموع زاويتين قائمتين، وبالتالي تنتقض العبارة.
راجع أيضاً
مصادر
- ^ Various Geometries
- ^ In "Appendix exhibiting the absolute science of space: independent of the truth or falsity of Euclid's Axiom XI (by no means previously decided)" (Faber 1983, pg. 161)
- ^ Greenberg cites W. Prenowitz and M. Jordan (Greenberg, p. xvi) for having used the term neutral geometry to refer to that part of Euclidean geometry that does not depend on Euclid's parallel postulate. He says that the word absolute in absolute geometry misleadingly implies that all other geometries depend on it.
- ^ Faber 1983, pg. 131
- ^ One sees the incompatibility of absolute geometry with elliptic geometry, because in the latter theory all triangles have angle sums greater than 180°.
- ^ Faber 1983, p. 296
- ^ Greenberg 2007, p. 163
- ^ Fine et al. 2022, Corollary 1.8, p. 11.
- ^ Indeed, absolute geometry is in fact the intersection of hyperbolic geometry and Euclidean geometry when these are regarded as sets of propositions.
- ^ Ewald, G. (1971), Geometry: An Introduction, Wadsworth
- ^ Coxeter 1969, pp. 175–6
- ^ Edwin B. Wilson & Gilbert N. Lewis (1912) "The Space-time Manifold of Relativity. The Non-Euclidean Geometry of Mechanics and Electromagnetics" Proceedings of the American Academy of Arts and Sciences 48:387–507
- ^ [1], a digest of the axioms used, and theorems proved, by Wilson and Lewis. Archived by Wayback Machine
- ^ Hartshorne 2005, p.97
- ^ Greenberg 2010, p.200
المراجع
- Coxeter, H. S. M. (1969), Introduction to Geometry (2nd ed.), New York: John Wiley & Sons
- Faber, Richard L. (1983), Foundations of Euclidean and Non-Euclidean Geometry, New York: Marcel Dekker, ISBN 0-8247-1748-1
- Fine, Benjamin; Moldenhauer, Anja; Rosenberger, Gerhard; Schürenberg, Annika; Wienke, Leonard (2022), Geometry and Discrete Mathematics: A Selection of Highlights, De Gruyter Textbooks (2nd ed.), Walter de Gruyter, ISBN 9783110740783
- Greenberg, Marvin Jay (2007), Euclidean and Non-Euclidean Geometries: Development and History (4th ed.), New York: W. H. Freeman, ISBN 0-7167-9948-0
- Greenberg, Marvin Jay (2010), "Old and New Results in the Foundations of Elementary Plane Euclidean and Non-Euclidean Geometries", Mathematical Association of America Monthly 117: 198–219, https://www.maa.org/sites/default/files/images/upload_library/22/Ford/Greenberg2011.pdf
- Hartshorne, Robin (2005), Geometry: Euclid and Beyond, New York: Springer-Verlag, ISBN 0-387-98650-2
- Pambuccain, Victor Axiomatizations of hyperbolic and absolute geometries, in: Non-Euclidean geometries (A. Prékopa and E. Molnár, eds.). János Bolyai memorial volume. Papers from the international conference on hyperbolic geometry, Budapest, Hungary, July 6–12, 2002. New York, NY: Springer, 119–153, 2006.
وصلات خارجية
Media related to هندسة مطلقة at Wikimedia Commons- Eric W. Weisstein, Absolute Geometry at MathWorld.