Q:

Why there are constant numbers in the universe?

Why the ratio of a circle's circumference to its diameter is always the constant $\pi$?
Moreover many of you know better about golden ratio $\phi$, Euler's number e, and many other constants. How explain this while everything seems to be in a complex system?

A:

$\pi, e,$ and $ \gamma$ are all mathematical constants. They are not dependent on the physical universe. For example, 
$$\pi = 4\left(1 - \frac{1}{3} + \frac{1}{5} - \frac{1}{7} + \ldots\right)$$
but it's unlikely for you to ask why the numbers, 4, 1, 3, 5, 7 aren't changing in a chaotic universe.
Real things aren't circles; circles are just math. For some real things, though, measurements of them can be well-approximated by circles.

