The discovery of the Big Bang – that the universe began about 13.7 billion years ago – is what breathes the fire into the Kalam Cosmological argument. You can see this by imagining a hypothetical debate between a Christian and an atheist before the disovery of the Big Bang.
Christian: How did the universe come to exist if God did not create it?
Atheist: How did God come to exist? Who created God?
Christian: No one created God. God has always existed.
Atheist: Exactly. No one made the universe, because the universe has always existed.
The discovery of the Big Bang took this last response away from atheists and permenantly redrew the battle lines in the process. The rest of the debate over the Kalam cosmological arguments consists of atheists trying to create a new defense that is just as good as “the universe has always existed.” But make no mistake, if an eternal universe were to once again become a live option, then atheists would promptly abandon these alternate responses.
The importance of the an eternal universe is not a Christian straw man. After the Big Bang atheists devised numerous theories to challenge the Big Bang and rescue the eternal universe. Einstein’s theory of relativity predicted the Big Bang, so he introduced a cosmological constant that made the universe eternal (Einstein was not an atheist, but he believed in an impersonal God and thus also needed the eternal universe). The problem was that he also divided by zero. He later called this mistake his “greatest blunder.”
Other physicists such as Fred Hoyle created the Steady State model, which predicted an eternal universe, as a rival to the Big Bang. They championed it for avowedly atheistic reasons. The discovery of cosmic background radiation falsified the steady state model. Another theory primary championed by Russian physicists, who were also atheists (as would be expected from a communist nation) is the oscillating model which predicted an endless cycle of expansions and collapses for the universe. That died with the discovery of dark energy in 1998. Another attempt was quantum vacuum fluctuations. Quantum mechanics tells us that vacuum is not really empty; it is filled with wrinkles and twists in the fabric of space-time itself. Changes (fluctuations) in these wrinkles give birth to subatomic particles. Perhaps this quantum vacuum is eternal, and the Big Bang was merely the result of a quantum vaccum fluctuations. That theory died in the 1980s because it actually predicts an infinite number of universe that would collide into each other and form larger universes like soap bubbles until you have one giant, infinitely old universe. Since we do not see evidence for this, the theory was rejected.
The Kalam Cosmological Argument
Now that it is clear that the universe is not eternal it is time to formally introduce the Kalam cosmological argument. It takes the form of one of Aristotle’s syllogisms:
(1) Whatever begins to exist has a cause
(2) The universe began to exist
(3) The universe has a cause
The phrase “begins to exist” is crucial. The Kalam argument is powerless against an eternal universe that was “always there.” For that you would have to use a more general first cause argument such as those of the medieval scholastic Saint Thomas Aquinas. But since we know that the universe is not eternal, the more powerful Kalam argument can be used instead. An interesting consequence is that arguments for the existence of God are stronger today than they were back in medieval times.
If you were to ask atheists who have not studied philosophy about the origins of the universe, it is safe to say that most of them would have assumed that there is a natural explanation for the cause of the Big Bang. They would be surprised to find out that the most popular atheistic objection to the Kalam argument is to claim that the Big Bang was uncaused. Not that it has an unknown cause, but that it has no cause at all. The origins of the universe cannot be studied scientifically, but must simply be accepted as brute fact. The Christian philosopher William Lane Craig who is the leading proponent of the Kalam cosmological argument calls this an escape route. But I would compare it to a secular miracle. A Christian miracle is “God did it.” A secular miracle is “it happened without any cause.”
Further Reading
See Kalam: Refuting the Standard Objections for a (mostly) plain English exploration of the standard objections.
Gentle Respect 