Thank you for an engaging reply. Working from a common basis of self-evident laws of logic, I will address the issues related to the topic of this commentary thread. I have grouped your responses together as they seemed closely related. If there is a specific point that you made that I have overlook, let me know.
You have basically simplified the question into "either the universe is necessary and does not need an explanation, or it is contingent and requires a necessary explanation". Then you effectively ruled out the former, and declared 'God' was the "necessary explanation". So, in effect, you have created a dichotomy, when in fact there are many other possible answers.
Why is infinite regress not allowable?
Because this would not explain why any contingent exists in the first place.
Perhaps, but 'God' doesn't explain why any contingent exists either. 'God' is simply a placeholder, an attempt to avoid admitting that you don't know what the explanation might be. In order to show that something explains something else, you must show how it does so, and not merely by saying that it's necessary, because that does not give it any explanatory power.
Demonstrating that something seems necessary (to you) in no way shows that it is necessary, or that it is not actually contingent on something else instead. That's why declaring that something is a "necessary entity" doesn't really work, because you have no way of knowing if it actually is one. Godel's incompleteness theorems apply here just as well as they do in math. You may be able to declare that there must be a necessary, unexplainable thing in order to explain the universe, but that in no way means that it actually is unexplainable.
What makes you think that the only non-contingent explanation is necessity? Just because all explanations must have the property of either contingency or non-contingency, it does not follow that non-contingent is synonymous with necessary. You have declared it so, but that's all you've done; you've made it part of your premise.
The only correction I see to your summary is that necessity is an explanation. If something exists necessarily, this means that it could not possibly not exist. Any need for further explanation, misunderstands the property of necessity.
You seemed to tacitly agree that infinite regress is a problem that should be avoided. However, your requirements for a valid explanation falls right back into that issue. If I ask why the water is boiling on the stove, you could explain it by talking about the activity of rapidly moving molecules or electrons. But such an explanation would, by your definition, be unsatisfactory, as now you would also have to explain every facet of the molecules and then every facet of energy and then every aspect of physical laws, and then...ad infinitum (to say nothing of a personal explanation for why the kettle is boiling i.e. you wanted to make tea). Under your standard, nothing could be considered an explanation until every piece of knowledge about everything was known.
However, in practice, when I ask why the kettle is boiling, and you say you are making tea, that is a perfectly valid and acceptable explanation. Or an explanation by way of a comprehensive, even if incomplete, detailing of molecules and energy will suffice. As I mentioned, if using the name 'God' is premature or confusing at this point, disregard it. We are still left with an explanation, whatever it might be, that will, in the very least, require the property of necessity.
Regarding necessity, this would seem to be a logically deduced requirement that in order to avoid an infinite regress, the explanation for why any thing contingent exists at all would have the property of necessity. If necessity is not synonymous with non-contingency, please provide a third option between contingency and necessity as no philosophical paper that I have read provides one.
As an example, the Stanford Encyclopedia for Philosophy:
"...4. What causes or explains the existence of this contingent being must either be solely other contingent beings or include a non-contingent (necessary) being. ...
....Premise 4 is true by virtue of the Principle of Excluded Middle: what explains the existence of the contingent being either are solely other contingent beings or includes a non-contingent (necessary) being." http://plato.stanford.edu/entries/cosmological-argument/#
Science supports a definite beginning to the universe and even, if cyclical, the conservation of entropy through the cycles prevents the cycles from occurring from an infinite past thus requiring a beginning.What science shows is that there's a point at which the universe was arbitrarily small and arbitrarily hot, not that it had a beginning. Furthermore, I have never heard of this "conservation of entropy" that you talk about. I've heard of the conservation of energy, but they are not the same thing. Do you perhaps mean the second law of thermodynamics? Even if that's the case, the second law does not make an infinite or cyclical past impossible, because the second law has to do with entropy in an isolated system. If the universe is not isolated (for example, if black holes ultimately act as 'drains' into another universe-space, as some scientists have argued), then there is no reason that entropy in the next universe-space could not be substantially less than it is here, because much of the entropy of this universe-space would stay here rather than being pulled through. There's other possibilities as well.
I was referring to the second law of thermodynamics. For any system to which this law applies (such as ours), an infinite past becomes extremely unlikely as it would allow an infinite amount of time which would allow an infinite amount of entropy to build. Since we are not in such a state, the universe could not have existed from infinite past but rather had a definite beginning.
Black hole universes, as theorized, attempts to get around the implications of the second law of thermodynamics. However, even if postulated by scientists, this is not an observable or scientifically verifiable theory. Further it seems that even Stephen Hawking in not in favor of this theory:
"Hawking also dismisses his previous suggestion that the information might have leaked into a different "Baby" universe. "The information remains firmly in our universe," he told the conference. "I am sorry to disappoint science fiction fans, but if information is preserved, there is no possibility of using black holes to travel to other universes. If you jump into a black hole, your mass energy will be returned to our universe, but in a mangled form which contains the information about what you were like, but in an unrecognisable state." http://physicsworld.com/cws/article/news/2004/jul/22/hawking-loses-black-hole-bet
I agree that there exists many logically possibilities for why the universe exists. However, it is important to make a distinction between logical possibility and epistemic possibility.
Logical possibility would allow any idea that is not logically contradictory to be consider rational. Under this criteria, the idea that we are brains in a vat of a mad scientist producing the illusion of reality and the idea that the universe is an actual reality in which persons exist are both equal rationally justified. This would, as you can see, invalidate knowledge of any kind, or perhaps, it would allow any logically consistent idea to count as knowledge. In either case, what would be the point of this discussion?
Epistemic possibility says something might be rational if there are good reasons to accept it as true, not merely the absence of logical contradiction. While we logically might be brains in a vat, there are no good reasons to think this is actually the case. Alternatively, there are good reasons to believe that our the universe does exist.
So while there are an infinite amount of logical possibilities that explain the appearance of the universe, not every possibility is epistemically possible. This point of logical and epistemic possibilities may not be an issue between yourself and I, but it seems to be pervasive in many posts on this forum. Skepticism can be a healthy and necessary pathway to knowledge; however, if we remain skeptical of any knowledge claim until all logical possibilities are exclude, knowledge becomes impossible, which is an absurdity.