I'm a Christian but I also enjoy science and am myself a reformed atheist so I'll go ahead and play devil's advocate. Apologetics can be fun but in my view the role of apologetics is to show that Christianity is reasonable, not to demonstrate that it is true. The difference between the two can be ambiguous, but I wouldn't consider any of the proofs or arguments used in apologetics to be in any way conclusive.
First Cause/Kalaam Cosmological Argument
Premise 1: Everything that begins to exist has a cause
Evidence: This is simply a casual relationship. Everything that BEGINS must have a cause in our universe due to the constraints of spacetime.
First, the premise that anything at all begins to exist is an assumption. According to the idea of conservation of matter and energy, neither matter nor energy (which are the same thing) can be created or destroyed. Therefore, if it cannot be created, it cannot begin to exist.
This is not a problem for the origin of the universe if the big bang singularity is supposed to have always existed, or if something is supposed to have existed before the big bang, from which the big bang was produced. Since we don't really know anything about the big bang singularity or what might have caused it or come before it, we can only speculate.
Additionally, the basic idea of causation is itself an assumption. Randomness and events without discernable causes are generally understood to be an inherent ingredient of quantum mechanics, which is currently our best and most fundamental understanding of nature (for example, virtual particles, which pop into existence in a seemingly random fashion and quickly annihilate one another, or wave functions, which are constrained by probability but whose outcome cannot even in principle be predicted).
Ultimately, this premise is just an argument from intuition (common sense). Intuitively, because of our interactions with the world on an everyday basis, we form ideas about things like causation, space, and time. However, one of the most important lessons we have learned from the revolutions of relativity, quantum mechanics, and cosmology is that our common-sense notions about the universe are suspect and usually wrong.
Common Objections:
Q: Why doesn't God have a cause?
A: The theistic understanding is that God is eternal and does not have a beginning. Ergo, Premise 1 does not apply to God
As is often pointed out, the same can just as easily be said about the universe.
Q: What about "virtual particles?"
A: Virtual particles require space time to exist so, in essence, they have a cause and exist within space and time.
The existence of spacetime doesn't qualify as a cause for virtual particles unless it's accompanied by a mechanism for producing them.
Premise 2: The universe began to exist
Evidence: Mathematical proof by Guth et al proves that universes such as ours come from a single point when spacetime is equal to zero. "Before" that "time" the universe did not exist.
As noted above, modern cosmology actually doesn't have anything to say about "time zero." Big bang theory and related cosmological theories attempt to describe what happened beginning a fraction fo a second after the big bang and continuing on from there, but are silent when it comes to the actual "bang." This is because our best current theories are unable to resolve the existing conflicts between relativity and quantum mechanics, both of which are required to work in concert in order to understand the workings of extremely small, extremely massive objects and events (such as black holes and the very early universe).
Common Objections:
None really as most atheists accept the Big Bang Theory
Conclusion: The Universe has a Cause
Furthermore: To prevent infinite regression there must be some Uncaused Cause.
As pointed out above, this could just be said to be the universe itself.
This Uncaused Cause must be powerful enough to create the universe and is outside spacetime and therefore eternal.
But not if it is itself the universe. This is why the cosmological argument doesn't really work.
Additionally, since causation and the conservation laws are basically just assumptions, there's no reason to suppose that the universe couldn't have come into existence spontaneously, without any cause or predecessor.
It is this Uncaused Cause that we call God.
