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the best discoveries don't take long to explain


From: David Farber <dave () farber net>
Date: Sat, 02 Apr 2005 05:34:33 -0500


------ Forwarded Message
From: Esther Dyson <edyson () edventure com>
Date: Fri, 01 Apr 2005 20:29:39 -0500
To: <dave () farber net>
Subject: the best discoveries don't take long to explain

note that this nice little groundbreaker comes in just 10 pages. and note
the last paragraph.

Esther Dyson

Classic maths puzzle cracked at last
17:53 21 March 2005
NewScientist.com news service
Maggie McKee

A number puzzle originating in the work of self-taught maths genius
Srinivasa Ramanujan nearly a century ago has been solved. The solution
may one day lead to advances in particle physics and computer security.

Karl Mahlburg, a graduate student at the University of Wisconsin in
Madison, US, has spent a year putting together the final pieces to the
puzzle, which involves understanding patterns of numbers.

"I have filled notebook upon notebook with calculations and equations,"
says Mahlburg, who has submitted a 10-page paper of his results to the
Proceedings of the National Academy of Sciences.

The patterns were first discovered by Ramanujan, who was born in India
in 1887 and flunked out of college after just a year because he
neglected his studies in subjects outside of mathematics.

But he was so passionate about the subject he wrote to mathematicians in
England outlining his theories, and one realised his innate talent.
Ramanujan was brought to England in 1914 and worked there until shortly
before his untimely death in 1920 following a mystery illness.

Curious patterns
Ramanujan noticed that whole numbers can be broken into sums of smaller
numbers, called partitions. The number 4, for example, contains five
partitions: 4, 3+1, 2+2, 1+1+2, and 1+1+1+1.

He further realised that curious patterns - called congruences -
occurred for some numbers in that the number of partitions was divisible
by 5, 7, and 11. For example, the number of partitions for any number
ending in 4 or 9 is divisible by 5.

"But in some sense, no one understood why you could divide the
partitions of 4 or 9 into five equal groups," says George Andrews, a
mathematician at Pennsylvania State University in University Park, US.
That changed in the 1940s, when physicist Freeman Dyson discovered a
rule, called a "rank", explaining the congruences for 5 and 7. That set
off a concerted search for a rule that covered 11 as well - a solution
called the "crank" that Andrews and colleague Frank Garvan of the
University of Florida, US, helped deduce in the 1980s.

Patterns everywhere
Then in the late 1990s, Mahlburg's advisor, Ken Ono, stumbled across an
equation in one of Ramanujan's notebooks that led him to discover that
any prime number - not just 5, 7, and 11 - had congruences. "He found,
amazingly, that Ramanujan's congruences were just the tip of the iceberg
- there were really patterns everywhere," Mahlburg told New Scientist.
"That was a revolutionary and shocking result."

But again, it was not clear why prime numbers showed these patterns -
until Mahlburg proved the crank can be generalised to all primes. He
likens the problem to a gymnasium full of people and a "big, complicated
theory" saying there is an even number of people in the gym. Rather than
counting every person, Mahlburg uses a "combinatorial" approach showing
that the people are dancing in pairs. "Then, it's quite easy to see
there's an even number," he says.

"This is a major step forward," Andrews told New Scientist. "We would
not have expected that the crank would have been the right answer to so
many of these congruence theorems."

Andrews says the methods used to arrive at the result will probably be
applicable to problems in areas far afield from mathematics. He and
Mahlburg note partitions have been used previously in understanding the
various ways particles can arrange themselves, as well as in encrypting
credit card information sent over the internet.



Esther Dyson              Always make new mistakes!
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