othergeeks:

In the academic world Dover Publications is widely known for publishing standard texts in mathematics. To me they’re known for publishing books with the best cover designs around, which truly make them stand out among the boring rest.

“Another picture from our wonderful blackboard artist Ryan Budney in Victoria, Canada. He’s taken a 4-dimensional sphere and removed a knotted 2-dimensional sphere (i.e. the surface of a beach ball), and tried to triangulate the resulting space. Triangulation means breaking up a complicated space into simpler pieces – triangles! – and then explaining how these pieces fit together. The triangulation here has precisely one vertex (a 0-dimensional triangle), one edge (a 1-dimensional triangle), 4 triangles (i.e. your usual garden-variety triangles), 5 tetrahedra (3D triangles) and the two pentachora (4-dimensional triangles).  The bottom picture shows how the pieces are glued together. The top picture is completely unrelated.
The knotted 2-dimensional sphere is called a Cappell-Shaneson knot because it is sitting inside a ‘homotopy 4-sphere’. That is, the space the knot is sitting in looks like a normal sphere from a distance but might turn out not to be upon closer inspection. If it isn’t, then it would provide a counterexample to the Poincaré Conjecture, which is still open in 4 dimensions (but was famously solved for 3 dimensions by Grigori Perelman in 2003).” Via What’s On My Blackboard?

“Another picture from our wonderful blackboard artist Ryan Budney in Victoria, Canada. He’s taken a 4-dimensional sphere and removed a knotted 2-dimensional sphere (i.e. the surface of a beach ball), and tried to triangulate the resulting space. Triangulation means breaking up a complicated space into simpler pieces – triangles! – and then explaining how these pieces fit together. The triangulation here has precisely one vertex (a 0-dimensional triangle), one edge (a 1-dimensional triangle), 4 triangles (i.e. your usual garden-variety triangles), 5 tetrahedra (3D triangles) and the two pentachora (4-dimensional triangles).  The bottom picture shows how the pieces are glued together. The top picture is completely unrelated.

The knotted 2-dimensional sphere is called a Cappell-Shaneson knot because it is sitting inside a ‘homotopy 4-sphere’. That is, the space the knot is sitting in looks like a normal sphere from a distance but might turn out not to be upon closer inspection. If it isn’t, then it would provide a counterexample to the Poincaré Conjecture, which is still open in 4 dimensions (but was famously solved for 3 dimensions by Grigori Perelman in 2003).” Via What’s On My Blackboard?

othergeeks:

Next time you’re at a party and want to leave an impression on someone say: “I bet you don’t know how to slice a doughnut into 13 pieces with just three cuts!” (This puts a very vivid image in my head of Ryan Gosling saying: “Hey Girl, do you know how to slice a doughnut into 13 pieces with only three cuts?”) 
From “The 2nd Scientific American Book of Mathematical Puzzles & Diversions” via the Reanimation Library, a really great project looking to resurrect “cultural debris.” They have some amazing images.

othergeeks:

Next time you’re at a party and want to leave an impression on someone say: “I bet you don’t know how to slice a doughnut into 13 pieces with just three cuts!” (This puts a very vivid image in my head of Ryan Gosling saying: “Hey Girl, do you know how to slice a doughnut into 13 pieces with only three cuts?”) 

From “The 2nd Scientific American Book of Mathematical Puzzles & Diversions” via the Reanimation Library, a really great project looking to resurrect “cultural debris.” They have some amazing images.

Reblogged from Fresh Photons
fuckyeahtopology:

This is a much more elegant representation of the problem on last week’s assignment that I was most proud of. My explanation wasn’t terribly clear, but at least it was correct, and I don’t know that anybody else managed that much. Oh, and if the problem isn’t clear, it’s to continuously deform a double torus into a double torus with linked arms, all without tearing or cutting anything, and without identifying and specific points. The way I was able to wrap my head around it involved stretching one lobe of the torus until it looks sort of like a thick coffee cup with no bottom and one handle. Then if you pinch the area where the handle connects (between the two connections really, you’re grabbing the inside of the hole of that lobe of the torus) and then pull it halfway through, so the two lobes are looped over each other. This shape is fairly easy to mold into the linked double torus.
image credit to the dying love grape, which seems to be a pretty interesting blog at least somewhat about maths.

fuckyeahtopology:

This is a much more elegant representation of the problem on last week’s assignment that I was most proud of. My explanation wasn’t terribly clear, but at least it was correct, and I don’t know that anybody else managed that much. Oh, and if the problem isn’t clear, it’s to continuously deform a double torus into a double torus with linked arms, all without tearing or cutting anything, and without identifying and specific points. The way I was able to wrap my head around it involved stretching one lobe of the torus until it looks sort of like a thick coffee cup with no bottom and one handle. Then if you pinch the area where the handle connects (between the two connections really, you’re grabbing the inside of the hole of that lobe of the torus) and then pull it halfway through, so the two lobes are looped over each other. This shape is fairly easy to mold into the linked double torus.

image credit to the dying love grape, which seems to be a pretty interesting blog at least somewhat about maths.

Non-orientability of the Klein bottle.

Non-orientability of the Klein bottle.