《数学与人类文明》Mathematics & Civilizations

《数学与人类文明》数学与现代文明：

1. 哲学：希腊 Euclidean Geometry

2. 艺术 : Arabic 文艺复兴， 达芬奇, Golden Ratio

3. 工业革命：Descartes Analytic Geometry, Newton Calculus

4. 抽象: Gauss “Non-Euclidean Geometry” , Paradox in Set Theory, Godel “Incomplete Theorem” .

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Symmetry Music Scores : 9 “Eigen” Notes 特征音符

This is a good mathematical symmetry trick to remember all musical notes thru 3 notes (1,4,5) in 9 positions.

Remember these 9 “Eigen“ Notes (C1, F4, G5) which are symmetric in position on the 5 lines, the other notes can be derived easily.

“Eigen” (German : characteristics 特征) as in Eigen vectors / Eigen values.

Green 4 (top ) & 5 (bottom)

Blue 5 (2nd line bottom up ) & 4 (2nd line top down)

Orange 1 (3rd space bottom up ) & 1 (3rd space top down)

https://m.toutiaoimg.cn/a6761794168806179331/?app=news_article_lite&is_hit_share_recommend=0

Music = Math + History

To really appreciate music, you must understand this Math & history :
5 notes to 7 notes to 12 notes.
& fractions: 3/2, 3/4, 2/1 (octave)

Music = Math + History

1. Ancient China 600 BC 管仲 (5 notes 宫商角徵\zhǐ羽）

2. Pythagoras 450 BC (7 notes, Chords 和弦)

3. Modern Music: 十二平均律 (明朝 1600 AD 朱载堉- > Bach 1700 AD)

https://m.toutiaoimg.com/group/6683391962764018183/?app=news_article_lite&timestamp=1581773659&req_id=20200215213418010194100050312DF0B9&group_id=6683391962764018183

Pythagoras did not believe in Irrational numbers (sqroot 2) , so only 7 integer notes.

17CE Chinese 明朝 Prince invented 12 notes music, using a giant 81-row Abacus to compute the12th root of 2 (picture below) ：

https://chinoiseries2014.wordpress.com/2019/02/07/%e5%8d%81%e4%ba%8c%e5%b9%b3%e5%9d%87%e7%8e%87/

十二平均律 12-tone Equal Temperament

《十二平均律》 是明朝 ＂布衣王子＂ 朱载堉 (1536年－1610年) 发明的，由当时在中国传教的意大利人 利马窦 (Matteo Ricci, 传给欧洲的法国数学家 Marin Mersenne (Mersenne Prime ) 。现代音乐之父 巴哈 Bach 第一个采用，制作世界第一架钢琴有12黑白键，并作曲 《Bach 12-tone Equal Temperament》。

$\boxed { \displaystyle \sqrt[12] {2} = 2^{\frac {1}{12} }= 2^{{\frac {1}{3}}.{\frac {1}{2}}.{\frac {1}{2}}} = \sqrt {\sqrt {\sqrt[3]{2}}}}$

Side Note:

1977年法国大学数学教授在课堂好奇地问我，你们祖先如何解代数？是用算盘吗？当时计算机还不流行，复杂的算法只能用Log Table 或 计算尺 (Slide Rule) 。

Bach 12-tone Equal Temperament

https://zh.m.wikipedia.org/wiki/%E5%8D%81%E4%BA%8C%E5%B9%B3%E5%9D%87%E5%BE%8B

Music and Mathematics (12 Tone Equal Temperament)- Dr. Eugenia Cheng (Prof Math in Category Theory)

Arrow’s Theorem

The Axioms for a fair voting system (eg. Political Election) :

1. Non-dictatorship:
◇ Outcome decided not by one ‘dictator’, but more than one person.

2. Unanimity
◇ If everyone votes that A is better than B, then A will be ranked higher than B in the final result.

3. Independence of irrelevant alternatives
◇ The ranking of A relative to B should not be affected by someone changing their mind about C.

Arrow’s Theorem says that if there are more than 2 people (parties) to vote for, then there is no fair voting system.

Note:
Most democratic voting systems violate the 3rd axiom (independence of irrelevant alternatives).