Original by Philip Gibbs, 1997.

Yes. *π* is a mathematical constant usually defined as the ratio of the
circumference of a circle to its diameter in euclidean geometry. It can also be
defined in other ways; for example, by using an infinite series:

π/4 = 1 - 1/3 + 1/5 - 1/7 + 1/9 - . . .

In general relativity, space and spacetime are non-euclidean geometries. The ratio of the
circumference to diameter of a circle in non-euclidean geometry can be more or less than π. For the
types of non-euclidean geometry used in physics, the ratio is very nearly *π* over small distances, and so
we do not notice the difference in ordinary measurements. This does not mean that *π* changes,
because our definition of *π* specified a euclidean geometry, not physical geometry. No new
theory or experiment in physics can change the value of mathematically defined constants.