Ex Nihilo

Ex nihilo nihil fit
-Parmenides-

The notion that "nothing comes from nothing" was first argued by pre-Socratic philosopher Parmenides. In the "Way of Truth", which constitutes the first part of his poem On Nature, he takes the emergence of something out of nothing as a logical impossibility, concluding that all existence is eternal, unchanging, and One. The appearance of change is just an illusion brought about by our senses, which are fallible. Reason alone can pierce the veil of impression, and glimpse the eternal truth: everything is One.

The Old Testament famously features a creation ex nihilo, and many religious people no doubt feel vindicated by the latest cosmological discoveries of a universe with a definite beginning, according to the Big Bang theory. However, things are not so simple. It is true that, according to our latest theories, the universe had a first moment in time (even though one should be wary of trusting a theory, General Relativity, that predicts singularities with infinite densities, and wait for a complete quantum theory of gravity, which could very well change the picture completely), but that does not necessarily mean that it was created.

Indeed, if it is true that our universe had a first moment, it is also true that Time doesn't exist outside of it. Time is a feature of our universe, and cannot be used as a meaningful concept outside of it. Stating that our universe was created, or came into existed at the moment of the Big Bang, presupposes some notion of time outside of its boundaries, or, put in another way, some notion of "before the first moment", which is nonsensical, like asking what's north of the north pole (this point has been made over and over again well before me).

The universe simply is, it exists, with no boundary in space and time,

...the universe has not existed forever.
Rather, the universe, and time itself, had a beginning in the Big Bang, about 15 billion years ago.
-Stephen Hawking-

No need for a creator, or any kind of creation ex nihilo. In fact, it is conceptually easier and more accurate to picture the universe as a space-time manifold (a topological space), like this

Conceptually, there's no difference between a big bang cosmology, with a beginning, and a bouncing cosmology, without a beginning, stretching infinitely back in time, as well as forward. Both are self-consistent entities, requiring no external input to function, no creation, and no prime mover. One just happens to have an earliest time, and the other doesn't. This view of the universe is called "eternalism" in philosophy of time, and it represents the view that all existence in time is equally real, and future existence is on the same footing as present existence, or past for that matter. This view goes very well together with the general theory of relativity, according to which the universe is to be understood as a space-time entity, or continuum, with time being ontologically no different than space. Just like all points in space are on the same footing, and all exists simultaneously, all points in time are the same, and future events are "already there" in the same sense other places are already there, and there is no objective flow of time.

This view is often contrasted with "presentism", i.e. the idea that only the present really exists, because past events have passed, and future events have not occurred yet. This is the most intuitive of the two, but, as it often happens, also the most difficult to defend from a scientific or even philosophical standpoint. Presentism is often associated to another pre-Socratic philosopher, Heraclitus, in many ways the intellectual rival of Parmenides, who said that "Panta Rhei", everything flows, and reality is in a state of constant flux.

In physics, Parmenides and Heraclitus contrasting views are embodied in the A and B theories of time. According to A-theory the flow of time is real, while B-theory argues that it is a subjective illusion of human consciousness, and temporal becoming is not an objective feature of reality. Kurt Gödel famously argued for B-theory by constructing a solution of GR that features closed timelike curves, i.e. spacetime curves that close, returning to the starting point, both in space and time. These curves, if possible, would allow time travel, and definitely dispel the idea that future and past are in any way different. For Gödel, the mere mathematical possibility of closed timelike curves in GR was enough to rule out A-theory, and vindicate the idea of a timeless Parmenidean universe.

In a four dimensional block universe (B-theory), time is intimately embedded within the structure of the cosmos, therefore asking temporal questions outside of it is meaningless. In A-theory, or presentism, the universe is more like an evolving block of space, with time being an absolute reference and ultimately non-physical, perhaps something even a creator would be subject to, given that the act of creation entails some notion of time.

Indeed, for an eternalist like Parmenides, or Gödel (or me), the difficulty in believing that our universe was "created" lies in the word itself, which, like many human words, has the idea of time embedded within it. For something to be created, a notion of time must be defined (an earlier time where that thing does not exist, and a later time where it comes into existence by some process), and while this is perfectly fine for events within the universe, it runs into trouble when we're trying to think about the creation of the universe itself, which by definition contains everything, time included.

Parmenides' philosophical argument against motion, change, and creation run much deeper than this, though. For Parmenides all these concepts share a common impossibility: the void. For something to truly change, or be created for that matter, that entity has to disappear into non-existence, and another, of a different quality, must appear into existence. This is inconceivable as non-existence, by definition, is not. Differences between things are also impossible, as that would imply some kind of void in between that separates them, which again, by definition, cannot exist.

Divine creation necessitates the void, in one form or the other, as God is believed to be creator but separate from its creation. The only way for anything to exist, Parmenides argues, is to exist completely, absolutely, and eternally, and since motion and separation are illusions, everything is One, a complementary participant, a part of the same whole. The universe is like a timeless jewel. A much more realistic depiction of God, if you ask me.