Sophie's Diary, book by Dora Musielak

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Sophie Germain
El Diario de Sofi
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Sophie Germain Home in Paris
18th Century Paris

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Sunday 7th of March 1790     

 

I was alone in the library playing chess when Papa came in with Monsieur de Maillard. He startled, moving a piece on the board and smiling he commented on my strategy. As he  settled in an armchair to drink coffee, M. de Maillard told me an extraordinary story about how the game originated. He said that chess is related to mathematics. I recount what he told me:

      Many centuries ago there was a king who wanted a unique game that no one else had, a game that was so original that it could be played over and over in endless combinations, a game that would teach the children of the royal family to become better thinkers and better leaders on the battlefield. With this in mind, a wise man invented the game that we now call chess. The king was very pleased, and he offered as a payment anything the man would want, gold, jewels, anything. The wise man asked to be paid with wheat grain. When asked how much, the man replied that he wanted the amount based on the number of squares on the game board.

     His formula was simple; for square one, he wanted one grain. For square two, it would be doubled to 2 pieces, for square three, it would be 4 pieces, for square four it would be 8 pieces, and so forth until all sixty four squares were filled in this proportion. The king was surprised by the seemingly modesty of this request, and he ordered a sack of wheat grain. The king’s servants patiently began to place the grain on each square on the board as requested by the wise man. Soon, they discovered that not even all the grain in the kingdom would be sufficient to cover half of the squares on the chessboard.

      M. de Maillard asked me if I could figure this out by myself. Hence, I will start by illustrating the distribution of wheat grain on the chessboard using numbers. Since there are 8 squares on the first row, I write:

 

1          2          4          8          16        32        64              128

 

in the second row:

256      512      1,024   2,048   4,096   8,192   16,384       32,768

 

in the third row:

65,536    131,072   262,144   524,288   1,048,576   2,097,152   4,194,304   8,388,608

chessboarda.jpg

Très bien! enough! I have to stop here. Now I just imagine the huge numbers on the squares of the fourth row and the remaining squares on the chessboard. Without doing the calculation I know that, on each square I can represent the number of grain by the number 2n, with the first square 20 = 1, and the number on the last square 2n = 263. Then I have to add the grain on all squares, making the total number of grain enormous. Even 263 is such a huge amount of grain that I cannot visualize it!

      I wonder how this story can be explained using only mathematics. Perhaps I can write a sum S equal to 1 plus 63 powers:

 

S = 1 + 21 + 22 + 23 + 24 + 25 + 26 + … + 261 + 262 + 263

 

Is this how mathematicians would analyze this problem?

chessboardb.jpg

A Historical Fiction book by Dora Musielak