(Book: On Guard, by William Lane Craig. Chapter 4: “Why did the universe begin?”)
We’re on a trip back to 12th-century Persia. Dr. Craig needs someone to rescue the Christian God from the perils of scientific advancement, and he thinks he has found a champion in a Muslim philosopher named Ghazali. (It’s amazing that Dr. Craig is able to successfully sell Muslim philosophy to conservative post-9/11 American Christians, don’t you think?) According to Ghazali, whatever begins to exist has a cause (premise 1), the universe began to exist (premise 2) and therefore the universe has a cause (conclusion).
Being a medieval Muslim philosopher, Ghazali did not have access to discoveries about particle physics and so on, so to prove premise number 2, he (and Dr. Craig) rely on philosophy. The argument is a bit flawed, however, in that it relies on a fundamental misunderstanding of what an infinity is. Curiously enough, it also contradicts the Christian doctrine of eternal life.
Ghazali argued that if the universe never began to exist, then there have been an infinite number of past events prior to today. But, he argued, an infinite number of things cannot exist… Ghazali recognized that a potentially infinite number of things could exist, but he denied that an actually infinite number of things could exist….When we say that something is potentially infinite, infinity serves merely as an ideal limit that is never reached. For example, you could divide distance in half, then into fourths, then into eights… The number of divisions is potentially infinite, in the sense that you could go on dividing endlessly. But you’d never arrive at an “infinitieth” division. You’d never have an actually infinite number of parts or divisions.
If there cannot be an actually infinite number of events in the past, then there also cannot be an infinite number of events in the future. Believers can get around this by saying that most of those events are only potential events because we haven’t experienced them yet. According to Christian cosmology, however, God exists outside of space and time, and is therefore not subject to the “haven’t experienced it yet.” All times are supposed to be immediately real to God, and thus if there cannot be an infinite number of them, then sooner or later there must come a day that will be the last day in the life of “immortal” believers and even God Himself. This means that, according to Dr. Craig’s arguments in Chapter 2, Christian life is devoid of all true meaning, value and purpose.