Perplexity
I don’t think (1) is very plausible. Or I should say, without any proposed reason to believe it I just kind of shrug my shoulders: it’s not obvious to me.
Here is Craig’s argument:
*f actual infinites that neither increase nor decrease in the number of members they contain were to exist, we would have rather absurd consequences. For example, imagine a library with an actually infinite number of books. Suppose that the library also contains an infinite number of red and an infinite number of black books, so that for every red book there is a black book, and vice versa. It follows that the library contains as many red books as the total books in its collection, and as many red books as red and black books combined. But this is absurd; in reality the subset cannot be equivalent to the entire set. Hence, actual infinites cannot exist in reality.
Kalam
A common objection to this argument is that Cantor set theory does not mathematically require this result; however, there are a couple of reasons why I believe it is inapplicable to Craig’s analysis. First, the Kalam argument is limited to the impossibility of an “actual” infinite - meaning that an infinite series of x cannot exist in the physical universe. Second, Craig’s use of the term “infinite” seems to reflect the algebraic definition of the absence of a bound.
With regard to aleph numbers, they are not (at least in my understanding) defined as infinite sets in the sense used by Craig. By definition the size of certain infinite sets are different from the size of others. I have no problem with this, and it is clear to me that mathematically the distinctions work. The issue I do have is that when reference is made to a “universe that has always existed” or “an infinite series of causes in the universe,” it is in fact a reference to a completely unbounded series with no limit. Cantorian set theory posits very very large “infinite” sets and subsets, but not limitless. My experience with the concept of infinity in mathematics is that it proxies (successfully) for very large quantities or numbers, but when applied to the ontological existence of the universe it is difficult to see how anything other than a series without bound is being posited.
(2) seems to assume a theory of time that I reject. I accept b-theory. So, for me, (2) makes about as much sense as saying that the segments of a ruler are formed by successive addition. But, of course the entire ruler exists regardless where, when or how you try to count its segments.
I don’t understand this objection. While the B-theory of time maintains tenseless propositions, it still describes a series of events. The argument stands that an actual infinite cannot exist, even with respect to a B-theory of time.*