Our readers may remember the original story with grains of rice. In other versions, the grains were wheat. Beyond the differences, its essence remains intact: In the end, the humble inventor of chess asked for much more than the king could deliver as a reward, and that conflict is one of the best examples of exponential growth we know. A Dutch teacher decided to put the famous legend onto a real board, and the result is wonderful.
The Legend and the Reward
“Name your reward and you shall have it,” the king had said (or emperor, depending on the version). After all, the creation of an exciting game like chess deserves proper recognition, and the king’s expression suggests a mix of spontaneous generosity and the classic arrogance of rulers. Now, some people believe the inventor really wanted food, and others that he sought to teach the king a lesson. That ambiguity is also reflected in the ending: One grain of rice for the first square, two for the second, four for the third, eight for the fourth... and so on until the last square. When scholars confirmed the chilling size of the request, the surprised king decided to turn the inventor into one of his most valuable advisers. The second version indicates that his request was interpreted as an act of arrogance, and the king decided to execute him. Which of the two endings is the real one? We don’t know. All we have left is chess, and a lot of rice.
The Project on a Real Board
18,446,744,073,709,551,615 grains, to be precise. A number impossible to visualize unless you apply a good dose of creativity. That brings us to the project by user “ajvdmeij” on Instructables, a teacher, DIY builder, and math enthusiast. His goal is to represent the exponential growth of rice grains on a chessboard, and to achieve it he used a series of polycarbonate tubes, different miniatures (the Eiffel Tower, the Burj Khalifa, a Magic Johnson figure), wood, and lots of glue. The tallest real tube measures 1.3 meters, and it barely reaches square 18. On square 26, the amount of rice needed would be taller than the Eiffel Tower. On square 36, it would almost touch the International Space Station. And on square 62... it would surpass the distance traveled by the Voyager 1 probe.
The total cost of materials is about 250 euros, but there is always room to improvise in these projects. “Ajvdmeij” did an excellent job here, and we are convinced that other teachers can use it as a basis to create their own visualizations of exponential growth.
