The temporal, kalam cosmological argument, dates back to medieval Muslim philosophers such as al-Kindi and al-Ghazali. It has recently been restored to popularity by William Lane Craig. Like all cosmological arguments, the kalam cosmological argument is an argument from the existence of the world or universe to the existence of God. The existence of the universe, such arguments claim, stands in need of explanation. The only adequate explanation, the arguments suggest, is that it was created by God.

What distinguishes the kalam cosmological argument from other forms of cosmological argument is that it rests on the idea that the universe has a beginning in time. Modal forms of the cosmological argument are consistent with the universe having an infinite past. According to the kalam cosmological argument, however, it is precisely because the universe is thought to have a beginning in time that its existence is thought to stand in need of explanation.

This argument has the following logical structure:

The Kalam Cosmological Argument

(1) Everything that has a beginning of its existence has a cause of its existence.
(2) The universe has a beginning of its existence.
Therefore:
(3) The universe has a cause of its existence.
(4) If the universe has a cause of its existence then that cause is God.
Therefore:
(5) God exists.

The first premise of the argument is the claim that everything that begins to exist has a cause of its existence. In order to infer from this that the universe has a cause of its existence the proponent of the kalam cosmological argument must prove that the past is finite, that the universe began to exist at a certain point in time.

The crucial premise of the kalam cosmological argument, then, is the second: “The universe has a beginning of its existence”. How do we know that the universe has a beginning of its existence? Might not the universe stretch back in time into infinity, always having existed? The proponent of the kalam cosmological argument must show that this cannot be the case if his argument is to be successful.

Advocates of the kalam cosmological argument claim that it is impossible that the universe has an infinite past. In support of this claim, modern advocates of the argument often appeal to modern science, specifically to the Big Bang theory. Modern science, they say, has established that the universe began with the Big Bang.

Traditionally, however, it is mathematics that has been used by proponents of the kalam argument in order to establish that the past is finite. There are a number of ways of doing this; I‘ll outline three mathematical arguments for the finitude of the past.