It's an arbitrary stopping point on the road of infinite regression.

What reason would anyone have to consider an unmoved mover? It just makes no sense.

Also, the opposite of magical creature isn't "chance". It's "I don't know", and not knowing is different than thinking you know exactly what it was (ie "chance" ).

I notice that this was never demonstrated. Somehow, does anything that causes something else have to be separated and completely unaffected from the result?

It doesn't seem to follow.

That is a completely unnecessary requirement.

The inability of the Greeks to come to terms with systems where the flow of cause does indeed loop-back and effect the outcome, a fundamental aspect of modern science, especially of biology, as well as their problems with infinite convergent sequences (Zeno's Paradox), or even irrational numbers, disqualifies them to be treated as authorities on anything technical. 

Quantum Theory strongly suggests that there truly is a fundamental randomness at the heart of reality, or at least something virtually equivalent, such as an indefinitely large number of interacting fundamental bits of reality, whose individual trajectory, like that of an individual molecule of oxygen in our atmosphere, is as close to being unpredictable as makes no difference.

This ability of 'determinism' to give rise to effective unpredictability, whether by such mechanism as just described, or by more specifically 'chaotic' feedback systems, is yet another thing 'traditional' philosophy and metaphysics has yet to come to terms with.

OK Syphro, could you speak to what your concept of an unmoved mover actually is?

I ask because the concept dropped into a discussion without some qualification is rather lacking in well, anything. Do you mean it to have been a conscious act on the part of a thinking being?

Consider the idea that the universe has existed for a finite amount of time. Well, I don't really see is as a shattering observation that something happened first. However, without some qualification, what was the thing that happened first?

On the face, that could have been a willful act of a conscious being, although that brings in a whole host of other issues that have already been pretty much beaten to death. It could also have been an unintentional act of a conscious being (what I call the “god farted” scenario) but that still leaves us with much the same problems.

A possible third option is the “shit happens” theory of creation, which is more or less in line with mainstream conjecture on the matter. The problem here is that it still doesn't say what happened or how anything else follows. Basically, in the big bang, what went bang?

As it happens, the big bang/inflationary cosmology doesn't take us there either. Really, all that that gives us is an accounting for a body of evidence that the universe is expanding and getting cooler over time. At the extreme edge of cosmological thought, we have entities such as dark matter and dark energy which are largely placeholder terms for stuff that we have not found just yet but seem to be required in order to make the rest of the body of cosmological thought coherent.

They could be real things or we could be missing important information that would point us in some other direction. Absent direct observation, we don't actually know. Even if we did have that stuff nailed down, it still does not reveal the origin of the universe so much as how the universe has developed since it began.

Well, in all honesty, I would not recommend that anyone start by reading Hawking. He skips over so much in a desire to get salable prose that he really is all about how cool science is without actually covering the truly cool bits to any great level.

If you have not already read it, I would recommend that you try Simon Singh's book titled “The Big Bang”. Honestly, he starts the book in ancient Greece and it takes him about half the book just to get to the 20^th century. Then he uses the other half to cover the most recent developments in some detail.