The Game of Rice


There's  a common maths problem that comes in various guises. The problem illustrates the concept of geometric series, sometimes called deterministic chaos, or more commonly the  power of exponential growth. I prefer a term coined by Yale.edu 'The unbearable quickness of doubling', or even better I like to think it of as 'how quickly things can get out of control'.

This is how it goes:

Apparently the ruler of India many years ago was delighted with the newly created game of chess. So pleased in fact that he wanted to reward its creator, who as it just so happens was somewhat of a wise man and full on mathematician. (Well what else would you expect from the creator of chess)?

The wise man appeared humble when he asked for simply 1 grain of rice to be placed on the first square of the chessboard on the first day, then double that number of grains of rice on the second square on the next day, and so on until all 64 squares had been filled.

It all sounded very simple and cheap and the ruler readily agreed. And sure enough it set off simple enough.

Square 1,  1 grain

Square 2,   2 grains

Square 3,   4 grains

By square 10, 512 grains. still not all that much.

 

This wise man's a fool thought the ruler. 

Square 20, 524,288 grains

Still within the bounds of reality and easy grasp of human thought.

Square 24, things are slipping a little out of bounds- it's up to over 8 million been added.

Then along comes day 32  and it's an amazing 2,147,483,648

And then something quite dreadful happens, it's at this half way point of doubling that things take a  shocking turn.

On day 36,  34,359,738,368 grains of rice are added.

by square 64 it's a whopping 9,223,372,036,854,775,808

 

It's an awful lot, in fact I'm told thats if all that rice was piled up it would reach the top of Everest. I haven't checked but feel free if you're inclined.

That wise man was no fool.

In fact the phrase the second half of the chessboard is often used to explain how quickly growth comes to have a significant impact on a businesses strategy and performance. In other words it's at the point of square 32, where things start to boom at extraordinary levels that businesses are really hit hard by the process of exponential growth.  At best its beyond chaos, at worst it's entirely unsustainable.


Square Grains on Square Running Total
1 1 1
2 2 3
3 4 7
4 8 15
5 16 31
6 32 63
7 64 127
8 128 255
9 256 511
10 512 1,023
11 1,024 2,047
12 2,048 4,095
13 4,096 8,191
14 8,192 16,383
15 16,384 32,767
16 32,768 65,535
17 65,536 131,071
18 131,072 262,143
19 262,144 524,287
20 524,288 1,048,575
21 1,048,576 2,097,151
22 2,087,152 4,194,303
23 2,097,152 8,388,607
24 8,388,608 16,777,215
25 16,777,216 33,554,431
26 33,554,432 67,108,863
27 67,108,864 134,217,727
28 134,217,728 268,435,455
29 268,435,456 536,870,911
30 536,870,912 1,073,741,823
31 1,073,741,824 2,147,483,647
32 2,147,483,648 4,294,967,295
33 4,294,967,296 8,589,934,591
34 8,589,934,592 17,179,869,183
35 17,179,869,184 34,359,738,367
36 34,359,738,368 68,719,476,735
37 68,719,476,736 137,438,953,471
38 137,438,953,472 274,877,906,943
39 274,877,906,944 549,755,813,887
40 549,755,813,888 1,099,511,627,775
41 1,099,511,627,776 2,199,023,255,551
42 2,199,023,255,552 4,398,046,511,103
43 4,398,046,511,104 8,796,093,022,207
44 8,796,093,022,208 17,592,186,044,415
45 17,592,186,044,416 35,184,372,088,831
46 35,184,372,088,832 70,368,744,177,663
47 70,368,744,177,664 140,737,488,355,327
48 140,737,488,355,328 281,474,976,710,655
49 281,474,976,710,656 562,949,953,421,311
50 562,949,953,421,312 1,125,899,906,842,623
51 1,125,899,906,842,624 2,251,799,813,685,247
52 2,251,799,813,685,248 4,503,599,627,370,495
53 4,503,599,627,370,496 9,007,199,254,740,991
54 9,007,199,254,740,992 18,014,398,509,481,983
55 18,014,398,509,481,984 36,028,797,018,963,967
56 36,028,797,018,963,968 72,057,594,037,927,935
57 72,057,594,037,927,936 144,115,188,075,855,871
58 144,115,188,075,855,872 288,230,376,151,711,743
59 288,230,376,151,711,744 576,460,752,303,423,487
60 576,460,752,303,423,488 1,152,921,504,606,846,975
61 1,152,921,504,606,846,976 2,305,843,009,213,693,951
62 2,305,843,009,213,693,952 4,611,686,018,427,387,903
63 4,611,686,018,427,387,904 9,223,372,036,854,775,807
64 9,223,372,036,854,775,808 18,446,744,073,709,551,615

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