(1) Identify a specific cause (e.g., God).
(2) Postulate that there must be a cause but that we cannot or do not yet know what it is.
(3) Claim that there is no cause and that the existence of the universe is simply a "brute fact."
(4) Deny that the question makes sense (It is like asking, "What is north of the North Pole?").
Yet, Law points out that there are difficulties with each answer. The problem with answer #1 is that it too requires a cause and that cause a cause leading to an infinite regress of causes. Answer #2 fares no better in that it still says there is cause, even if it is not yet known, and that there must, therefore, be an infinite regress of causes. Answer #3 simply seems unreasonable. And the fact that answer #4 is controversial among philosophers suggests that it is untenable.
My own current inclination is to go with answer #3, but I take a different tack than the one Law takes. Law says that answer #3 entails accepting as "brute fact" that the universe simply "popped into existence" without cause or reason. But I ask why the universe ever had to have come into existence. That is, why must we assume that there was ever a natural nothing? Why could we not assume that there was always a natural something that now comprises natural reality as we know it?
Here is how David Mills, in his outstanding book Atheist Universe, defends this idea:
But what about Mortimer Adler's question: "Why is there something rather than nothing?"...From a scientific perspective, though, the question is: Why shouldn't there be something rather than nothing? What law of science claims that the universe is not supposed to exist or that nonexistence is the "natural" condition? There is no such law. On the contrary, the law of the conservation of mass-energy leads to a radically different conclusion: that the mass-energy which now constitutes our universe always existed, though this universe, as we observe it today, did indeed have a beginning at the Big Bang. (p. 94)When I read this passage from Mills, it struck me with the force of an intellectual explosion. Unless I encounter good reason to think otherwise, I believe that this is a very reasonable way to look at the existence of the universe and a compelling objection to the argument that the universe had to have been created out of nothing by God.