Hyperbolic Geometry, Elliptic Geometry, and Euclidean Geometry
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Hyperbolic Geometry
Hyperbolic Geometry David Gu Yau Mathematics Science Center Tsinghua University Computer Science Department Stony Brook University [email protected] September 12, 2020 David Gu (Stony Brook University) Computational Conformal Geometry September 12, 2020 1 / 65 Uniformization Figure: Closed surface uniformization. David Gu (Stony Brook University) Computational Conformal Geometry September 12, 2020 2 / 65 Hyperbolic Structure Fundamental Group Suppose (S; g) is a closed high genus surface g > 1. The fundamental group is π1(S; q), represented as −1 −1 −1 −1 π1(S; q) = a1; b1; a2; b2; ; ag ; bg a1b1a b ag bg a b : h ··· j 1 1 ··· g g i Universal Covering Space universal covering space of S is S~, the projection map is p : S~ S.A ! deck transformation is an automorphism of S~, ' : S~ S~, p ' = '. All the deck transformations form the Deck transformation! group◦ DeckS~. ' Deck(S~), choose a pointq ~ S~, andγ ~ S~ connectsq ~ and '(~q). The 2 2 ⊂ projection γ = p(~γ) is a loop on S, then we obtain an isomorphism: Deck(S~) π1(S; q);' [γ] ! 7! David Gu (Stony Brook University) Computational Conformal Geometry September 12, 2020 3 / 65 Hyperbolic Structure Uniformization The uniformization metric is ¯g = e2ug, such that the K¯ 1 everywhere. ≡ − 2 Then (S~; ¯g) can be isometrically embedded on the hyperbolic plane H . The On the hyperbolic plane, all the Deck transformations are isometric transformations, Deck(S~) becomes the so-called Fuchsian group, −1 −1 −1 −1 Fuchs(S) = α1; β1; α2; β2; ; αg ; βg α1β1α β αg βg α β : h ··· j 1 1 ··· g g i The Fuchsian group generators are global conformal invariants, and form the coordinates in Teichm¨ullerspace. -
Squaring the Circle in Elliptic Geometry
Rose-Hulman Undergraduate Mathematics Journal Volume 18 Issue 2 Article 1 Squaring the Circle in Elliptic Geometry Noah Davis Aquinas College Kyle Jansens Aquinas College, [email protected] Follow this and additional works at: https://scholar.rose-hulman.edu/rhumj Recommended Citation Davis, Noah and Jansens, Kyle (2017) "Squaring the Circle in Elliptic Geometry," Rose-Hulman Undergraduate Mathematics Journal: Vol. 18 : Iss. 2 , Article 1. Available at: https://scholar.rose-hulman.edu/rhumj/vol18/iss2/1 Rose- Hulman Undergraduate Mathematics Journal squaring the circle in elliptic geometry Noah Davis a Kyle Jansensb Volume 18, No. 2, Fall 2017 Sponsored by Rose-Hulman Institute of Technology Department of Mathematics Terre Haute, IN 47803 a [email protected] Aquinas College b scholar.rose-hulman.edu/rhumj Aquinas College Rose-Hulman Undergraduate Mathematics Journal Volume 18, No. 2, Fall 2017 squaring the circle in elliptic geometry Noah Davis Kyle Jansens Abstract. Constructing a regular quadrilateral (square) and circle of equal area was proved impossible in Euclidean geometry in 1882. Hyperbolic geometry, however, allows this construction. In this article, we complete the story, providing and proving a construction for squaring the circle in elliptic geometry. We also find the same additional requirements as the hyperbolic case: only certain angle sizes work for the squares and only certain radius sizes work for the circles; and the square and circle constructions do not rely on each other. Acknowledgements: We thank the Mohler-Thompson Program for supporting our work in summer 2014. Page 2 RHIT Undergrad. Math. J., Vol. 18, No. 2 1 Introduction In the Rose-Hulman Undergraduate Math Journal, 15 1 2014, Noah Davis demonstrated the construction of a hyperbolic circle and hyperbolic square in the Poincar´edisk [1]. -
Elliptic Geometry Hawraa Abbas Almurieb Spherical Geometry Axioms of Incidence
Elliptic Geometry Hawraa Abbas Almurieb Spherical Geometry Axioms of Incidence • Ax1. For every pair of antipodal point P and P’ and for every pair of antipodal point Q and Q’ such that P≠Q and P’≠Q’, there exists a unique circle incident with both pairs of points. • Ax2. For every great circle c, there exist at least two distinct pairs of antipodal points incident with c. • Ax3. There exist three distinct pairs of antipodal points with the property that no great circle is incident with all three of them. Betweenness Axioms Betweenness fails on circles What is the relation among points? • (A,B/C,D)= points A and B separates C and D 2. Axioms of Separation • Ax4. If (A,B/C,D), then points A, B, C, and D are collinear and distinct. In other words, non-collinear points cannot separate one another. • Ax5. If (A,B/C,D), then (B,A/C,D) and (C,D/A,B) • Ax6. If (A,B/C,D), then not (A,C/B,D) • Ax7. If points A, B, C, and D are collinear and distinct then (A,B/C,D) , (A,C/B,D) or (A,D/B,C). • Ax8. If points A, B, and C are collinear and distinct then there exists a point D such that(A,B/C,D) • Ax9. For any five distinct collinear points, A, B, C, D, and E, if (A,B/E,D), then either (A,B/C,D) or (A,B/C,E) Definition • Let l and m be any two lines and let O be a point not on either of them. -
Cross-Ratio Dynamics on Ideal Polygons
Cross-ratio dynamics on ideal polygons Maxim Arnold∗ Dmitry Fuchsy Ivan Izmestievz Serge Tabachnikovx Abstract Two ideal polygons, (p1; : : : ; pn) and (q1; : : : ; qn), in the hyperbolic plane or in hyperbolic space are said to be α-related if the cross-ratio [pi; pi+1; qi; qi+1] = α for all i (the vertices lie on the projective line, real or complex, respectively). For example, if α = 1, the respec- − tive sides of the two polygons are orthogonal. This relation extends to twisted ideal polygons, that is, polygons with monodromy, and it descends to the moduli space of M¨obius-equivalent polygons. We prove that this relation, which is, generically, a 2-2 map, is completely integrable in the sense of Liouville. We describe integrals and invari- ant Poisson structures, and show that these relations, with different values of the constants α, commute, in an appropriate sense. We inves- tigate the case of small-gons, describe the exceptional ideal polygons, that possess infinitely many α-related polygons, and study the ideal polygons that are α-related to themselves (with a cyclic shift of the indices). Contents 1 Introduction 3 ∗Department of Mathematics, University of Texas, 800 West Campbell Road, Richard- son, TX 75080; [email protected] yDepartment of Mathematics, University of California, Davis, CA 95616; [email protected] zDepartment of Mathematics, University of Fribourg, Chemin du Mus´ee 23, CH-1700 Fribourg; [email protected] xDepartment of Mathematics, Pennsylvania State University, University Park, PA 16802; [email protected] 1 1.1 Motivation: iterations of evolutes . .3 1.2 Plan of the paper and main results . -
+ 2R - P = I + 2R - P + 2, Where P, I, P Are the Invariants P and Those of Zeuthen-Segre for F
232 THE FOURTH DIMENSION. [Feb., N - 4p - (m - 2) + 2r - p = I + 2r - p + 2, where p, I, p are the invariants p and those of Zeuthen-Segre for F. If I is the same invariant for F, since I — p = I — p, we have I = 2V — 4p — m = 2s — 4p — m. Hence 2s is equal to the "equivalence" in nodes of the point (a, b, c) in the evaluation of the invariant I for F by means of the pencil Cy. This property can be shown directly for the following cases: 1°. F has only ordinary nodes. 2°. In the vicinity of any of these nodes there lie other nodes, or ordinary infinitesimal multiple curves. In these cases it is easy to show that in the vicinity of the nodes all the numbers such as h are equal to 2. It would be interesting to know if such is always the case, but the preceding investigation shows that for the applications this does not matter. UNIVERSITY OF KANSAS, October 17, 1914. THE FOURTH DIMENSION. Geometry of Four Dimensions. By HENRY PARKER MANNING, Ph.D. New York, The Macmillan Company, 1914. 8vo. 348 pp. EVERY professional mathematician must hold himself at all times in readiness to answer certain standard questions of perennial interest to the layman. "What is, or what are quaternions ?" "What are least squares?" but especially, "Well, have you discovered the fourth dimension yet?" This last query is the most difficult of the three, suggesting forcibly the sophists' riddle "Have you ceased beating your mother?" The fact is that there is no common locus standi for questioner and questioned. -
Arxiv:1210.8144V1 [Physics.Pop-Ph] 29 Oct 2012 Rcs Nw Nti a Ehv Lme Oad H Brillia the Enlightenment
Possible Bubbles of Spacetime Curvature in the South Pacific Benjamin K. Tippett∗ Department of Mathematics and Statistics University of New Brunswick Fredericton, NB, E3B 5A3 Canada In 1928, the late Francis Wayland Thurston published a scandalous manuscript in purport of warning the world of a global conspiracy of occultists. Among the documents he gathered to support his thesis was the personal account of a sailor by the name of Gustaf Johansen, describing an encounter with an extraordinary island. Johansen’s descriptions of his adventures upon the island are fantastic, and are often considered the most enigmatic (and therefore the highlight) of Thurston’s collection of documents. We contend that all of the credible phenomena which Johansen described may be explained as being the observable consequences of a localized bubble of spacetime curvature. Many of his most incomprehensible statements (involving the geometry of the architecture, and variability of the location of the horizon) can therefore be said to have a unified underlying cause. We propose a simplified example of such a geometry, and show using numerical computation that Johansen’s descriptions were, for the most part, not simply the ravings of a lunatic. Rather, they are the nontechnical observations of an intelligent man who did not understand how to describe what he was seeing. Conversely, it seems to us improbable that Johansen should have unwittingly given such a precise description of the consequences of spacetime curvature, if the details of this story were merely the dregs of some half remembered fever dream. We calculate the type of matter which would be required to generate such exotic spacetime curvature. -
MATH32052 Hyperbolic Geometry
MATH32052 Hyperbolic Geometry Charles Walkden 12th January, 2019 MATH32052 Contents Contents 0 Preliminaries 3 1 Where we are going 6 2 Length and distance in hyperbolic geometry 13 3 Circles and lines, M¨obius transformations 18 4 M¨obius transformations and geodesics in H 23 5 More on the geodesics in H 26 6 The Poincar´edisc model 39 7 The Gauss-Bonnet Theorem 44 8 Hyperbolic triangles 52 9 Fixed points of M¨obius transformations 56 10 Classifying M¨obius transformations: conjugacy, trace, and applications to parabolic transformations 59 11 Classifying M¨obius transformations: hyperbolic and elliptic transforma- tions 62 12 Fuchsian groups 66 13 Fundamental domains 71 14 Dirichlet polygons: the construction 75 15 Dirichlet polygons: examples 79 16 Side-pairing transformations 84 17 Elliptic cycles 87 18 Generators and relations 92 19 Poincar´e’s Theorem: the case of no boundary vertices 97 20 Poincar´e’s Theorem: the case of boundary vertices 102 c The University of Manchester 1 MATH32052 Contents 21 The signature of a Fuchsian group 109 22 Existence of a Fuchsian group with a given signature 117 23 Where we could go next 123 24 All of the exercises 126 25 Solutions 138 c The University of Manchester 2 MATH32052 0. Preliminaries 0. Preliminaries 0.1 Contact details § The lecturer is Dr Charles Walkden, Room 2.241, Tel: 0161 27 55805, Email: [email protected]. My office hour is: WHEN?. If you want to see me at another time then please email me first to arrange a mutually convenient time. 0.2 Course structure § 0.2.1 MATH32052 § MATH32052 Hyperbolic Geoemtry is a 10 credit course. -
Of Rigid Motions) to Make the Simplest Possible Analogies Between Euclidean, Spherical,Toroidal and Hyperbolic Geometry
SPHERICAL, TOROIDAL AND HYPERBOLIC GEOMETRIES MICHAEL D. FRIED, 231 MSTB These notes use groups (of rigid motions) to make the simplest possible analogies between Euclidean, Spherical,Toroidal and hyperbolic geometry. We start with 3- space figures that relate to the unit sphere. With spherical geometry, as we did with Euclidean geometry, we use a group that preserves distances. The approach of these notes uses the geometry of groups to show the relation between various geometries, especially spherical and hyperbolic. It has been in the background of mathematics since Klein’s Erlangen program in the late 1800s. I imagine Poincar´e responded to Klein by producing hyperbolic geometry in the style I’ve done here. Though the group approach of these notes differs philosophically from that of [?], it owes much to his discussion of spherical geometry. I borrowed the picture of a spherical triangle’s area directly from there. I especially liked how Henle has stereographic projection allow the magic multiplication of complex numbers to work for him. While one doesn’t need the rotation group in 3-space to understand spherical geometry, I used it gives a direct analogy between spherical and hyperbolic geometry. It is the comparison of the four types of geometry that is ultimately most inter- esting. A problem from my Problem Sheet has the name World Wallpaper. Map making is a subject that has attracted many. In our day of Landsat photos that cover the whole world in its great spherical presence, the still mysterious relation between maps and the real thing should be an easy subject for the classroom. -
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Arxiv:1808.05573V2 [Math.GT] 13 May 2020 A.K.A
THE MAXIMAL INJECTIVITY RADIUS OF HYPERBOLIC SURFACES WITH GEODESIC BOUNDARY JASON DEBLOIS AND KIM ROMANELLI Abstract. We give sharp upper bounds on the injectivity radii of complete hyperbolic surfaces of finite area with some geodesic boundary components. The given bounds are over all such surfaces with any fixed topology; in particular, boundary lengths are not fixed. This extends the first author's earlier result to the with-boundary setting. In the second part of the paper we comment on another direction for extending this result, via the systole of loops function. The main results of this paper relate to maximal injectivity radius among hyperbolic surfaces with geodesic boundary. For a point p in the interior of a hyperbolic surface F , by the injectivity radius of F at p we mean the supremum injrad p(F ) of all r > 0 such that there is a locally isometric embedding of an open metric neighborhood { a disk { of radius r into F that takes 1 the disk's center to p. If F is complete and without boundary then injrad p(F ) = 2 sysp(F ) at p, where sysp(F ) is the systole of loops at p, the minimal length of a non-constant geodesic arc in F with both endpoints at p. But if F has boundary then injrad p(F ) is bounded above by the distance from p to the boundary, so it approaches 0 as p approaches @F (and we extend it continuously to @F as 0). On the other hand, sysp(F ) does not approach 0 as p @F . -
Math 181 Handout 16
Math 181 Handout 16 Rich Schwartz March 9, 2010 The purpose of this handout is to describe continued fractions and their connection to hyperbolic geometry. 1 The Gauss Map Given any x (0, 1) we define ∈ γ(x)=(1/x) floor(1/x). (1) − Here, floor(y) is the greatest integer less or equal to y. The Gauss map has a nice geometric interpretation, as shown in Figure 1. We start with a 1 x × rectangle, and remove as many x x squares as we can. Then we take the left over (shaded) rectangle and turn× it 90 degrees. The resulting rectangle is proportional to a 1 γ(x) rectangle. × x 1 Figure 1 Starting with x0 = x, we can form the sequence x0, x1, x2, ... where xk+1 = γ(xk). This sequence is defined until we reach an index k for which xk = 0. Once xk = 0, the point xk+1 is not defined. 1 Exercise 1: Prove that the sequence xk terminates at a finite index if { } and only if x0 is rational. (Hint: Use the geometric interpretation.) Consider the rational case. We have a sequence x0, ..., xn, where xn = 0. We define ak+1 = floor(1/xk); k =0, ..., n 1. (2) − The numbers ak also have a geometric interpretation. Referring to Figure 1, where x = xk, the number ak+1 tells us the number of squares we can remove before we are left with the shaded rectangle. In the picture shown, ak+1 = 2. Figure 2 shows a more extended example. Starting with x0 =7/24, we have a1 = floor(24/7) = 3. -
A Brief Survey of Elliptic Geometry
A Brief Survey of Elliptic Geometry By Justine May Advisor: Dr. Loribeth Alvin An Undergraduate Proseminar In Partial Fulfillment of the Degree of Bachelor of Science in Mathematical Sciences The University of West Florida April 2012 i APPROVAL PAGE The Proseminar of Justine May is approved: ________________________________ ______________ Lori Alvin, Ph.D., Proseminar Advisor Date ________________________________ ______________ Josaphat Uvah, Ph.D., Committee Chair Date Accepted for the Department: ________________________________ ______________ Jaromy Kuhl, Ph.D., Chair Date ii Abstract There are three fundamental branches of geometry: Euclidean, hyperbolic and elliptic, each characterized by its postulate concerning parallelism. Euclidean and hyperbolic geometries adhere to the all of axioms of neutral geometry and, additionally, each adheres to its own parallel postulate. Elliptic geometry is distinguished by its departure from the axioms that define neutral geometry and its own unique parallel postulate. We survey the distinctive rules that govern elliptic geometry, and some of the related consequences. iii Table of Contents Page Title Page ……………………………………………………………………….……………………… i Approval Page ……………………………………………………………………………………… ii Abstract ………………………………………………………………………………………………. iii Table of Contents ………………………………………………………………………………… iv Chapter 1: Introduction ………………………………………………………………………... 1 I. Problem Statement ……….…………………………………………………………………………. 1 II. Relevance ………………………………………………………………………………………………... 2 III. Literature Review …………………………………………………………………………………….