to understand vs to understanding [duplicate]

I was wondering why we use "understanding" instead of "understand" in this sentence? can we just use "understand"?

Math is the hidden secret to understanding the world.

understanding the world is a gerund (it doesn't include "to"). The gerund can stand on its own as an object.

If you want to use the infinitive (a different use of "to"), you need an auxiliary verb, for example:

Math is the hidden secret needed to understand the world.