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- Why is Mathematics Possible: Tim Gowers's Take on the Matter
- New Ramanujan Graphs!
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# Monthly Archives: May 2013

## Joram’s Memorial Conference

Joram Lindenstrauss 1936-2012 This week our local Institute of Advanced Study holds a memorial conference for Joram Lindenstrauss. Joram was an immensely powerful mathematician, in terms of originality and conceptual vision, in terms of technical power, in terms of courage to confront … Continue reading

## Andriy Bondarenko Showed that Borsuk’s Conjecture is False for Dimensions Greater Than 65!

The news in brief Andriy V. Bondarenko proved in his remarkable paper The Borsuk Conjecture for two-distance sets that the Borsuk’s conjecture is false for all dimensions greater than 65. This is a substantial improvement of the earlier record (all dimensions … Continue reading

## Why is mathematics possible?

Spectacular advances in number theory Last weeks we heard about two spectacular results in number theory. As announced in Nature, Yitang Zhang proved that there are infinitely many pairs of consecutive primes which are at most 70 million apart! This is a sensational achievement. … Continue reading

## Dan Mostow on Haaretz and Other Updates

Enlightenment at a red traffic light Wolf Prize laureate Prof. George Daniel Mostow made his greatest scientific breakthrough while driving. Haaretz tells the story of how Dan Mostow reached his breakthrough known as Mostow’s rigidity theorem. Congratulations, Dan! French-Isreali Meeting … Continue reading

## Test Your Intuition (21): Auctions

You run a single-item sealed bid auction where you sell an old camera. There are three bidders and the value of the camera for each of them is described by a certain (known) random variable: With probability 0.9 the value … Continue reading

Posted in Economics, Games, Test your intuition
Tagged Auctions, Roger Myerson, Test your intuition
4 Comments

## Oz’ Balls Problem: The Solution

A commentator named Oz proposed the following question: You have a box with n red balls and n blue balls. You take out each time a ball at random but, if the ball was red, you put it back in the box and take out … Continue reading

Posted in Probability, Test your intuition
Tagged Erosion, J. F. C. Kingman, Probability, S. E. Volkov
1 Comment

## Answer: Lord Kelvin, The Age of the Earth, and the Age of the Sun

Yeshu Kolodni and Lord Kelvin The question In 1862, the physicist William Thomson (who later became Lord Kelvin) of Glasgow published calculations that fixed the age of Earth at between 20 million and 400 … Continue reading

Posted in Geology, Physics, Test your intuition
4 Comments

## Test your Intuition/Knowledge: What was Lord Kelvin’s Main Mistake?

The age of the earth (Thanks to Yeshu Kolodny) We now know that the age of the earth is 4.54±1% Billion years. From Wikipedea: In 1862, the physicist William Thomson (who later became Lord Kelvin) of Glasgow published calculations that … Continue reading

Posted in Controversies and debates, Geology, Physics, Test your intuition
Tagged Earth, Geology, Lord Kelvin, Test your intuition
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## Indian Crested Porcupine

For a few days we had an Indian Crested Porcupine (דורבן) in our garden. It ate all the flowers and dug an impressive array of tunnels.

## New Ramanujan Graphs!

Margulis’ paper Ramanujan graphs were constructed independently by Margulis and by Lubotzky, Philips and Sarnak (who also coined the name). The picture above shows Margulis’ paper where the graphs are defined and their girth is studied. (I will come back to the question … Continue reading

Posted in Algebra and Number Theory, Combinatorics, Open problems
Tagged Ramanujan graphs
10 Comments