As in Babylonia, Indian scientists made a lot of progress in geometry as a result of interest in astronomy. By 1300 BC the Indian astronomer Lagadha used geometry to write a book of rules to predict the movement of the sun and moon as they seemed to move around the earth. (Nobody knew yet that the earth goes around the sun.) Did Lagadha work these rules out on his own? Or did he learn about them from the Babylonians? Nobody knows.
By about 400 BC, a little after the time of the Buddha, Indian mathematicians were doing more work on the idea of infinity. The Surya Prajinapti defines five kinds of infinity: an infinite line beginning from an endpoint, an infinite line going both directions, an infinite plane, an infinite universe, and the infinity of time.
Around 300 BC, when Chandragupta was ruling India, Indian mathematicians began working on the mathematical idea of combinations. This is the study of how many combinations you can make out of the same group of things. For example, how many different poker hands can you make out of a pack of cards? Or, what are the chances that in any class of thirty kids, some of them will share the same birthday? Indian mathematicians worked on how you could figure that out. They published their ideas in a book called the Bhagabati Sutra.
Indian mathematicians’ biggest contribution was the use of zero as a placeholder. Zero made it easier to add and multiply numbers. Our word “zero” comes from the Sanskrit word meaning “nothing.” Chinese mathematicians had already been using a blank space to mean “zero” for several hundred years, but Indian mathematicians created the empty circle to be clearer. In 458 AD, Indian mathematicians wrote a book, the Lokavibhaaga, that uses zero in this way.
