The First Cause Argument

The first cause argument (or “cosmological argument”) takes the existence of the universe to entail the existence of a being that created it. It does so based on the fact that the universe had a beginning. There must, the first cause argument says, be something that caused that beginning, a first cause of the universe.

The universe consists of a series of events stretched across time in a long causal chain. Each one of these events is the cause of the event that comes after it, and the effect of the event that comes before it. The world as it is came from the world as it was, which came from the world as it was before.
If we trace this series of events back in time, then what do we find? There seem, at first glance, to be two possibilities: either we eventually reach the first event in the series, the cause at the beginning of the universe that set everything going, or there is no first event in the series and the past stretches back into infinity.

The first cause argument tells us that the second of these is not possible, that the past cannot stretch back into infinity but rather must have a beginning. The argument then proceeds by suggesting that if the universe has a beginning then there must be something outside it that brought it into existence.

This being outside the universe, this Creator, the first cause argument tells us, is God.

It’s Impossible to Traverse an Infinite Series

If I told you that I had just counted down from infinity to zero, starting with “infinity minus zero” and carrying on until I reached “infinite minus infinity, i.e zero”, then you would know that this claim is false. Just as it is impossible to count up from zero to infinity, so it is impossible to count down from infinity to zero. If I had started counting down from infinity and kept going, then I would still be counting to this day; I would not have finished. My claim to have counted down from infinity to zero must be false. This is because it is impossible to traverse an infinite series.

The Past Therefore Cannot be Infinite

The idea that the universe has an infinite past is just as problematic as the idea that I have just counted down from infinity. If the universe had an infinite past, then time would have had to count down from infinity to reach time zero, the present, and so would not have reached it. The fact that we have reached the present therefore shows that the past is not infinite but finite. The universe has a beginning. This claim, of course, has been confirmed by modern science, who trace the universe back to a point of origin in the ‘big bang’.
The past cannot go back forever, then; the universe must have a beginning. The next question is whether something caused this beginning, or whether the universe just popped into existence out of nothing. We all know, though, that nothing that begins to exist does so without a cause; nothing comes from nothing. For something to come into existence there must be something else that already exists that can bring it into existence. The fact that the universe began to exist therefore implies that something brought it into existence, that the universe has a Creator.

The First Cause Must be Uncreated, Eternal

If this Creator were a being like the universe, a being that exists in time and so that came into existence, then it too would have to have been created by something. Nothing comes from nothing, not even God.
This tells us that the ultimate cause of the universe must never have come into existence; the ultimate Creator must be a being that exists outside of time, an eternal being with neither beginning nor end. (For a more detailed defence of this argument, see William Lane Craig’s The Existence of God and the Beginning of the Universe.)

What the First Cause Argument Proves
There are several objections to the first cause argument, but if it is successful then it establishes the existence of a Creator that transcends time. Combined with the ontological argument, this would give us proof that there is a perfect, necessary, and eternal Creator.

This would not quite be the same as proving all that Christianity and the other monotheistic religions teach about God, but it would be close. It would tell us that God exists, and what he is like, and that he created the universe. It would not, however, tell us why he created the universe or what we ought to do about it.

The final two arguments speak more about God’s purpose in Creation, and so at least hold out the hope of completing this picture. The first of these two arguments is the argument from design.

http://www.existence-of-god.com/first-cause-argument.html