Of Eru

[Voronwe]

First there was nothin and time passed, so the odds were that something would eventually come to pass.

Methinks that the Universe was around forever, never created, never will be destroyed

I suggest you take a glance at any Popular Science book on cosmology.

Thankfully, such questions are side-stepped in Tolkien's universe. It is essentially taken as axiomatic that Eru was the ultimate 'first cause', creating all things and needing no creator. Whether one agrees this is possible or not doesn't matter; Tolkien is simply writing about a reality in which this is the case.