85 Light rays bouncing in twisted tubes 2011-07-15T10:59:06.393

70 Is the sphere the only surface all of whose projections are circles? Or: Can we deduce a spherical Earth by observing that its shadows on the Moon are always circular? 2010-09-17T18:02:19.583

68 Light reflecting off Christmas-tree balls 2010-12-22T12:59:23.840

50 Tying knots with reflecting lightrays 2010-09-15T11:56:24.910

46 What do Weierstrass points look like? 2009-12-17T21:57:25.473

38 Is there a mathematical axiomatization of time (other than, perhaps, entropy)? 2011-03-08T12:56:29.990

34 Sheaves and bundles in differential geometry 2010-03-08T23:07:20.150

30 Why is the Laplacian ubiquitous? 2011-02-10T04:43:38.150

29 "Softness" vs "rigidity" in Geometry 2012-12-11T21:50:40.823

25 Why is the half-torus rigid? 2011-10-10T23:01:04.417

23 Rolle's theorem in n dimensions 2010-01-01T21:51:09.710

23 Geometry of complex elliptic curves 2011-06-27T18:34:07.753

22 Is there a topological description of combinatorial Euler characteristic? 2009-10-19T07:59:04.597

21 Minimal surface in a ball 2009-11-03T17:27:18.030

21 A Weak Form of Borsuk's Conjecture 2012-07-23T15:13:46.767

20 Is there a combinatorial analogue of Ricci flow? 2011-05-22T05:16:29.440

20 Random Distance Matrices 2011-11-02T18:16:14.403

17 Turning pants inside-out (or backwards) while tied together 2010-04-18T23:39:55.583

17 What can be said about the Shadow hull and the Sight hull? 2010-09-18T17:43:59.517

17 Arrangements of points in the plane 2010-12-30T07:19:19.537

17 Placing points on a sphere so that no 3 lie close to the same plane 2011-12-03T16:27:05.330

16 A question about the proof of Mostow rigidity 2010-04-20T16:40:01.360

16 Which norms have rich isometry groups? 2011-05-10T01:07:06.470

16 When does the set of isometries form a group? 2011-09-17T16:10:14.113

15 Can all convex polytopes be realized with vertices on surface of convex body? 2012-09-13T14:35:23.617

15 Does every connected set that is not a line segment cross some dyadic square? 2013-01-31T14:07:14.780

15 Integer lattice points on a hypersphere 2013-05-22T22:20:02.673

14 Use of n-transitivity in finite group theory 2009-10-24T13:11:01.217

14 The Symmetry of a Soccer Ball 2010-03-29T18:08:23.750

14 Totally rational polytopes 2011-08-03T01:29:14.860

14 How far is a set of vectors from being orthogonal? 2012-05-18T15:48:28.823

14 Approximating a convex function by a piecewise linear function 2012-09-28T13:04:26.623

13 When do two holonomy maps determine flat bundles that are isomorphic as just bundles (w/o regard to the flat connections)? 2010-03-04T08:15:30.397

13 A characterization of convexity 2010-06-21T16:23:24.043

13 When sticks fall, will they weave? 2010-06-27T01:51:44.260

13 Fixed point theorems and equiangular lines 2010-07-07T14:20:52.183

13 Geodesic metrics that admit dilatation at each point 2010-09-25T17:19:01.487

13 orientations for zero-dimensional manifolds 2010-11-28T17:06:30.663

13 Geometric interpretation of Cartan's structure equations 2011-04-15T23:00:42.823

13 Optimal Wireframe Sphere 2012-04-11T13:09:22.210

12 Upper bound on the area of a midpoint pentagon? 2009-11-08T02:34:59.810

12 Finding Constant Curvature Metrics on Surfaces without full power of Uniformization 2010-02-07T20:31:03.047

12 geometry of null homotopies 2010-08-19T18:40:53.507

12 Effective contraction of a loop. Reference or a simple proof? 2010-09-21T19:28:19.883

12 Cheap, non-constructive, free group generating rotations for Banach-Tarski 2010-12-14T07:31:32.690

12 Which platonic solids can form a topological torus? 2011-01-28T11:44:32.707

12 F→E→B bundle with B,E,F hyperbolic: possible? 2011-05-25T21:46:56.583

12 Periodic lightray paths trapped between two nested mirror circles 2012-01-09T03:44:44.410

12 There are two points on the Earth's surface that ... ? 2012-11-18T01:13:11.027

12 Limiting shape for Brillouin zones 2015-10-23T13:52:44.673

12 Find structure geometry of $A_1, A_2,...,A_n$ such that $\prod_{i<j} A_iA_j$ is maximum 2016-09-04T04:20:25.097

11 Making an l_2 distance out of l_1 distance 2009-10-25T06:08:30.107

11 Geometry of the multilagrangian Grassmannian 2009-12-17T20:54:21.887

11 Prescribing Gaussian curvature 2010-03-09T02:09:09.790

11 creating high quality figures of surfaces 2010-05-25T16:55:15.137

11 Shortest-path Distances Determining the Metric? 2010-05-26T23:52:40.017

11 "minimal" embedding of bipartite graphs on a sphere 2010-12-09T05:01:37.113

11 Is there a complete classification of constant mean curvature surfaces? 2010-12-24T19:11:34.130

11 Who conjectured that a transitive projective plane is Desarguesian? 2011-06-01T07:06:44.187

11 On the definition of regularity 2011-08-22T18:47:41.423

11 For what metrics are circles solutions of the isoperimetric problem? 2012-06-26T09:07:02.150

11 Polyominoes with double contact 2013-01-02T12:57:47.073

11 To what extent does trajectory determine gravity sources? 2013-02-09T01:11:15.983

11 Dao's theorem on six circumcenters associated with a cyclic hexagon 2016-03-19T17:06:36.653

10 A "round" lattice with low kissing number? 2009-10-23T18:00:22.143

10 Diameter of universal cover 2009-12-11T05:57:36.900

10 Ordered geometries from convex subsets of the plane 2010-02-03T13:40:33.317

10 Dissecting trapezoids into triangles of equal area 2010-05-29T03:16:52.820

10 Triangle centers as power sum minimizing points: Which is the locus of all these points? 2010-05-29T22:58:17.787

10 Decomposing the plane into intervals 2010-10-26T01:36:49.313

10 Non-Kahler Complex manifolds 2010-11-17T00:19:58.677

10 Floating polyhedra with fair equilibria 2010-12-31T02:36:58.657

10 The "grassmannian" of a simplicial complex 2012-01-23T10:54:18.027

10 Altitudes of a triangle 2012-07-09T14:04:42.950

10 A strange question about closed geodesics on a closed manifold 2012-07-26T02:26:40.520

10 Optimization of points on a plane 2015-12-08T01:49:21.890

9 Minimize Perimeter(S)/Area(S) for S inside the unit square. 2009-11-11T06:15:47.853

9 Characterizing a tumbling convex polytope from the surface areas of its two-dimensional projections 2010-05-14T14:05:44.910

9 How many non-equivalent sections of a regular 7-simplex? 2010-09-20T20:17:23.263

9 Rigidity of triangle comparison in Alexandrov spaces 2010-11-05T12:40:23.063

9 Do elongated convex objects all have long simple geodesics? 2011-01-11T13:40:57.603

9 What is the "right" definition of the homology(cohomology) of an orbifold? 2011-10-05T15:35:13.743

9 is a group $G$, that admits finite $k(G, 1)$ and has no Baumslag-Solitar subgroups, necessarily hyperbolic? 2011-11-29T13:02:23.753

9 Why are isometries of Minkowski space necessarily linear? 2011-12-29T23:49:57.927

9 Can one do without a classifying space when showing vanishing of cohomology 2012-02-01T07:03:27.123

9 Ellipsoids and lattices: an enclosure problem. 2012-02-08T20:12:58.297

9 Recognising group actions on trees from the boundary 2012-05-18T12:57:50.790

9 About MF Atiyah and R Bott's 1983 paper 2012-10-25T13:23:33.660

9 Minimum separation among $m$ random points on an $n$-dimensional unit sphere 2016-07-25T06:28:19.293

8 Coiling Rope in a Box: Decidable? 2010-06-10T00:48:58.600

8 Maximum number of mutually equidistant points in an n-dimensional Euclidean space is (n+1). Proof? 2010-07-02T04:53:27.173

8 Expected number of steps for a discrete random walk to visit every point on an N-dimensional rectangular lattice 2010-08-16T14:23:06.740

8 Do singular values of a point set determine its shape? 2010-12-21T19:47:06.710

8 Coloring toroidal polyhedra with convex faces? 2011-02-03T19:26:24.003

8 The volume of the “unit ball” in $\mathbb{R}^{m\times n}$ with respect to the cut norm 2011-02-21T21:15:16.340

8 Will a ball fired through a focus of an ellipse eventually tend to a horizontal line? 2011-03-21T11:57:31.930

8 Dense sphere packings which are not lattice packings 2011-04-07T10:18:48.653

8 Eigenvalues of Laplacian-Beltrami operator 2011-05-05T15:53:17.923

8 $G$-structures of finite type. 2011-05-05T23:25:23.393