Follow a point on the rim of a wheel as it rolls (without slipping) on a flat road and you'll get a cycloid. It's a beautiful curve with all sorts of interesting applications. [Wiki bit.ly/2St3vmA] #50FamousCurves
Fun fact: The area under one arch of a cycloid is exactly three times the area of its generating circle. #50FamousCurves
Fun fact: The period of a cycloidal pendulum is independent of its amplitude. (This isn't the case for the simple pendulum.) This was discovered by Huygens in his search for more accurate pendulum clock designs ≈350 years ago. #50FamousCurves
[Gif source: Wikipedia, Rem088roy]
Watch @thinktwice2580's latest video for an easy-to-understand explanation.
Fun fact: The cycloid is the brachistochrone curve i.e. the curve of fastest descent. Finding this out was a challenge posed by Johann Bernoulli in 1696 and solved by several great mathematicians of the time (including Leibniz and Newton). #50FamousCurves
The history of the brachistochrone problem is fascinating. I recommend watching @3blue1brown's video that he made with @stevenstrogatz on the topic.
Earlier this year a friend* and I've solved a long-standing problem which, in part, meant finding the eigenvectors of this matrix. In this thread, I'll review our result and bits of 170 years of history
*J.F. van Diejen, Talca
1/n
The title of our paper is "Elliptic Kac–Sylvester Matrix from Difference Lamé Equation" and it was recently published in the mathematical physics journal Annales Henri Poincaré.
Just to "name-drop" some of the characters that will appear in the story: Sylvester (duh), Jacobi, Boltzmann, two Ehrenfests, Schrödinger and Kac (obvs).
(I'll expand the thread over several days so please be patient.)
3/n
"Here's a photo of my boy, Peter. He doesn't yet know what the continuum is, but he doesn't know what fascism is either." - George Szekeres' message to Paul Erdős.
Peter Szekeres was born in Shanghai, where his parents George Szekeres and Esther Klein escaped from Nazi persecution in 1938.
Happy Ending Theorem: any set of five points in the plane in general position has a subset of four points that form the vertices of a convex quadrilateral.
Erdős gave this name to the theorem, because it led to the marriage of Szekeres and Klein
As a run-up to the "Introduction to Integrability" series (see my pinned tweet), I decided to share some interesting bits from the history of integrable systems.
Let's start at the beginning, shall we? So Newton...
#1 It all started with Newton solving the gravitational 2-body problem and deriving Kepler's laws of planetary motion as a result. I would argue that this was possible, because the Kepler problem is (super)integrable. [1/2]
This roughly means that there are many conversed physical quantities like energy, angular momentum, and the Laplace-Runge-Lenz vector. These conservation laws restrict the motion and allow for explicit analytic solutions of otherwise difficult equations. [2/2]