pi is the ratio of circumference to diameter.That is true in a flat, Cartesian space. In a curved space, a physicist measuring the ratio of the circumference of a circle to its diameter will come up with a different value, which will be more or less than pi depending on which way his space is curved. But a mathematician will calculate the ratio of circumference to diameter, and come up with pi, won't he? So, pi is universal? But our measurement of it depends on our space?