Again, talking a bit outside my comfort zone, but I believe our universe's physics say that circles only have a fixed circumference-to-radius ratio at "small" (astronomically) scales. At large enough scales space is curved and the ratio begins to change.
In a similar way, a set of different physics would apply to small enough aliens that are principally governed by quantum mechanics. They might never come up with the real numbers because they do not believe that quantities are dense.
We could think of more examples -- aliens who typically move at speeds close to the speed of light would have very different conceptions of time, etc.
Our best estimate for the topology of the universe at the largest scale is that it is 'flat'. If it has curvature, it's below the margin of error we are able to measure it at. The only thing we know that can curve space significantly is gravity, but it would take truly stupendously strong gravity fields to significantly change basic results from classical geometry, such as those close to the event horizon of a black hole. Even then we can calculate it accurately nowadays so our results would still correspond to theirs even in those circumstances.
In a similar way, a set of different physics would apply to small enough aliens that are principally governed by quantum mechanics. They might never come up with the real numbers because they do not believe that quantities are dense.
We could think of more examples -- aliens who typically move at speeds close to the speed of light would have very different conceptions of time, etc.