Monthly Archives: February 2010

Test Your Intuition (11): Is it Rational to Insure a Toaster

Posted on February 28, 2010 by Gil Kalai

Here is a question from last year’s exam in the course “Basic Ideas of Mathematics”:   You buy a toaster for 200 NIS ($50) and you are offered one year of insurance for 24 NIS ($6).   a) Is it … Continue reading →

Posted in Probability, Rationality, Teaching, Test your intuition | Tagged , | 18 Comments

The Beauty of Mathematics

Posted on February 24, 2010 by Gil Kalai

This semester I am teaching an introductory course in mathematics for students in other departments.  I taught a similar course last year entitled “Basic Ideas in Mathematics,” and this year, following a suggestion of my wife, I changed the name to “The Beauty of Mathematics”. Another … Continue reading →

Posted in Teaching | 26 Comments

Nerves of Convex Sets – A Recent Result by Martin Tancer

Posted on February 23, 2010 by Gil Kalai

Martin Tancer recently found a very beautiful proof that finite projective planes can’t be represented by convex sets in any fixed dimension. This was asked in the paper entitled “Transversal numbers for hypergraphs arising in geometry” by Noga Alon, Gil … Continue reading →

Posted in Convexity | 2 Comments

Itamar Pitowsky: Probability in Physics, Where does it Come From?

Posted on February 15, 2010 by Gil Kalai

I came across a videotaped lecture by Itamar Pitowsky given at PITP some years ago on the question of probability in physics that we discussed in two earlier posts on randomness in nature (I, II). There are links below to … Continue reading →

Posted in Obituary, Philosophy, Physics, Probability | Tagged , , , | 2 Comments

Noise Stability and Threshold Circuits

Posted on February 10, 2010 by Gil Kalai

The purpose of this post is to describe an old conjecture (or guesses, see this post) by Itai Benjamini, Oded Schramm and myself (taken from this paper) on noise stability of threshold functions. I will start by formulating the conjectures and … Continue reading →

Posted in Combinatorics, Computer Science and Optimization, Probability | Tagged , , , , | 14 Comments

The Möbius Undershirt

Posted on February 9, 2010 by Gil Kalai

“Look at this brand new undershirt,” my wife said. “I am shaking it and shaking it but still I have this twist.  Can you see what to do?”  I gave the undershirt a good shake. And another one. And one more. And … Continue reading →

Posted in Mathematics to the rescue, Taxi-and-other-stories | Tagged , , , | 5 Comments

Anat Lotan: Who is Gina II, My Own Shocking Revelation

Posted on February 5, 2010 by Gil Kalai

Who’s Gina? (Part 2): My Own Shocking Revelation By: Anat Lotan It was one of those typically hot Israeli end-of-August days; a scorching summer morning, where you have to convince yourself that the cool breezes of autumn are just around … Continue reading →

Posted in Gina Says, Guest blogger | Tagged , | 4 Comments

Anat Lotan: Who is Gina I

Posted on February 5, 2010 by Gil Kalai

  Several people asked me to explain who is Gina, the hero of my book “Gina says:  Adventures in the Blogosphere String War.” There was a chapter written by Anat Lotan about who Gina is.  And in view of the … Continue reading →

Posted in Gina Says | Tagged , | 2 Comments

A Discrepancy Problem for Planar Configurations

Posted on February 3, 2010 by Gil Kalai

Yaacov Kupitz and Micha A. Perles asked: What is the smallest number C such that for every configuration of n points in the plane there is a line containing two or more points from the configuration for which the difference between the … Continue reading →

Posted in Combinatorics | Tagged , | 3 Comments

The Ultimate Riddle

Posted on February 2, 2010 by Gil Kalai

 Click on the picture!

Posted in Riddles | Tagged | 15 Comments