Credible/Honest Apologetics?

[R00tKiT]

Premise 1 is referring to the things we observe in the universe, beginning to exist from other stuff that already exists; trees, chairs, animals, cars, etc. This is creation ex materia.

That's not what Premise 1 refers to, that's your personal interpretation of it. Both premises refer to creation ex nihilo, not ex materia. It's a mundane fact that things like cars didn't begin to exist the moment they are assembled, "cars" are assembled items that are useful to us, and these items obviously existed before, it's the meaning of the term "car" that began to exist once we figured out how to make them.

 As you can see "creation ex materia" is just wordplay, there is no creation, just cobbling stuff together. 

This is an equivocation fallacy, using the same word(s), "begins to exist", to mean 2 different things; ex materia in one premise, ex nihilo in another premise.

As I clarified above, there is only one meaning of "begins to exist" that is interesting in this argument, and that is creation ex nihilo -no need to double down on the word creation since it begs the existence of a creator, I am just using it for the lack of a better word-

Kalam also contains the fallacy of composition.

Just because parts of the universe begin to exist, does not mean the universe itself began to exist.

I am not sure there is a fallacy of composition in this particular case. It's like saying: just because your body parts are made of flesh and blood, does not mean you are not made of flesh and blood. If the word "you" is exactly identical to the sum of your body parts, then I don't think it's a fallacy to conclude that you are in fact flesh and blood, from the observation that each of your body parts/organs is flesh and blood.

Same with the universe, what else does the word "universe" mean if not the sum of its parts, let's denote the content of the whole universe U (its energy, for example) and its different parts P_i. Then:

U=P_1 + P_2 + ... + P_n.

Since the universe is finite in size, there will be finite terms in the sum above, so there is no paradox or confusion about the possibility of infinite terms. Now how can we formalize the idea that each P_i began to exist in the simple formula above? well let's add the subscript t to denote time, U_t is simply the total energy of the universe at the moment t, so:

U_t = P_1,t + P_2,t + ... P_n,t

Now you don't need to use more than one brain cell to see that if each term of the sum above is 0 when t=0, U_0 must also be equal to 0

Which leads to the main contentious premise. How do we know the universe began to exist? It is quite possible, that the universe always existed, but just in another form.

There is only one compelling argument that I know of trying to establish that the universe began to exist. Assume the universe is indeed past infinite, now in order to get to the present moment, you have to exhaust infinitely many moments in the past, in other words, it took an infinitely long period of time for the present moment to happen, obviously this is a contradiction.