Dr. Craig is a liar.

[SteveII]

My point is that Carroll believes
 
Oh.  I thought you said that all atheists do believe (or should believe?) that the universe is without explanation.  That would be an absurd claim, patently false. 
 
that the universe (or its quantum vacuum predecessor)
 
If the universe is everything that exists, including time, then it can't have a predecessor. 

That depends on what model you are hanging your hat on, but that does not matter. Carroll understands the problem. Going back however many steps you think it takes does not escape the problem of the past infinite causes. Do you believe the universe began or are you willing to live with the absurdity of an infinite regression?

does not exist necessarily (could have failed to exist) and that it has existed from infinity with no explanation--a "brute fact" as he also put it.
 
Like your god?
 
He does not believe in God so that is not an explanatory option for him.
 
I don't think gods are ever explanatory.

So you are willing to believe, despite the logical absurdity and scientific evidence, that the universe is past eternal or sprang from nothing uncaused but deny that God can't be an explanatory option?

Other atheists might have a slightly different idea about universe generators, endless expansion/contraction, etc. but that does not escape the problem of eventually you have to say something always existed (brute fact) 
 
So many ways to approach that.  Let me just ask, how is it different with gods? 

BTW, this type of argument is part of natural theology. Natural theology is examining attributes and properties of God through examining reality and using logic rather than appealing to the Bible. To avoid the problems above, you need an uncaused first cause. Just by examining the problem, you get the properties of this entity: eternal, timeless, powerful enough to make something out of nothing, non-physical, has intent, etc.

even in the face of the absurdity of a past infinite.  
 
I don't see how an unbegun infinite past is any more absurd than a begun finite past.  Both present conceptual difficulties greater than I can cope with. 
 
I can't say, "X must be true because Y is weird," when X and Y seem to be equally weird.  If Y's weirdness made X true, then X's weirdness would also make Y true, which would result in contradiction.  So I think the rational response is to say we don't  know. 
 
I wandered onto campus one day to check out this no-infinities assertion that Christians make.  I found three physics professors, and put the question to them:  Do infinities exist in real life?   None of them opined that infinities do not exist.

 
You perhaps did not phrase the question right. Infinites in math is a conceptual tool. It is used in equations (which of course physicist use). There are an infinite number of real numbers. We are talking about actual infinities. There is no way to get to infinity by adding one at a time--you will never get there. Causal chains and time are created by adding. The same principle applies going into the past. You could never had arrived at today without there being a yesterday and a day before. You could never get to today as the end of a causal chain without all the causes before adding one to another.

A) If atheism is true, the universe (or its predecessors) has no explanation of its existence.

If your claim is that this is the claim of this Carroll person, I'll have to take your word for it.  But if your claim is that this claim is logically entailed by atheism, then I'd like to see you make your case.

see above

If you believe A) to be true then you also believe B) If the universe (or its predecessor) has an explanation of its existence, then atheism is not true because it is the logical equivalent. You cannot affirm A) and deny B) --they rise and fall together.
 
I don't want to nitpick.  I can say it this way:
 
The premise, "If there are no gods, then the universe has no explanation," logically entails the conclusion, "If the universe has an explanation, then there is at least one god." 
 
I agree that that premise entails that conclusion.

That's fine. Occam's razor would dictate that we consider only one at this stage, but that's fine with me.