Let's engage one of the best arguments there is for the existence of God. It's called the Kalam Cosmological Argument. Before we look at the argument it's important to note a few things.
This argument is based soundly on the notion that it is impossible to have an infinite number of past events.
This argument is also based upon sound logical reasoning and as such in order to refute the argument one would have to show one of the premises false or that the conclusion does not follow.
The main goal of this argument is to show that there is a first cause, not to prove the existence of the Christian God. This is important to understand.
I believe this argument is the best argument to start with when addressing a skeptic because it lays a foundation for other arguments and eventually for the God of the Bible.
Simple right? Now let’s look at each step and check its validity. Let's dive in shall we. The argument is straightforward and easy to memorize. There are just three simple steps.
Whatever begins to exist requires a cause.
The universe began to exist
Therefore the universe has a cause.
Simple right? Now let’s look at each step and check its validity.
1. Whatever begins to exist requires a cause:
First and foremost, to deny this premise is to deny a fundamental metaphysical principle and go against the fact that matter can neither be created nor destroyed and science in general. Something cannot come out of nothing. This should be completely obvious to everyone.
Nothing comes from nothing. If this weren’t true we would see things appearing in front of us constantly. In fact Craig would say that it’s so obvious that the premise stands on its own. However you may encounter one argument to this premise and that is “Who created God then?” But this is an illogical question because God is necessarily uncaused.
2. The universe began to exist:
I mentioned earlier that this argument is soundly based upon the idea that it’s impossible to have an actual infinite number of past events; here’s why. Today is built on yesterday and yesterday on the day before and the day before on the day before that, etc. Each day is a single thing and knowing that we are here today would imply that a finite number of days have passed one by one. If there are an infinite number of days in the past we would never be able to reach this point in time because there is always one more day at the beginning or, more so, there would be an infinite number of points between and two points in time.
A string or recent scientific discoveries also imply that the universe had a beginning.
The expansion of the universe suggests that the it is not infinite because if you trace this expansion back in time we witness the universe getting more and more dense until it reaches a singular point from which the universe begins to expand.
We witness this expansion of the universe by viewing the distances between galaxies growing, the red shifting of light from cosmic object and what’s called cosmic background radiation.
General Relativity does not permit for an infinite universe. This eventually led to Big Bang theory.
The second law of thermodynamics suggests that in a closed system everything moves towards equilibrium. Basically this means that after certain amount of time the universe will slow down and die what I’ve heard referred to as a “heat death.” Since we are still here we know that hasn’t happened yet so, the universe cannot be infinitely old.
3. The universe had a cause:
From the two premises above it is logical to conclude that the universe had a cause. But what was this cause? Before the universe there was nothing: no time, space or matter. So the cause must be non-temporal (eternal), non-physical, and non-material. So what could satisfy these requirements?
Because there are only two kinds of things that are non-material the cause can only be one of two possible things, an abstract object like a number or a mind. We know that abstract objects don’t cause anything. Minds do however. It is here that we can conclude that a non-physical, non-temporal, and immaterial creator must have been the cause of all we see and experience. By very definition this is God.
This is a very simple argument to memorize but one that can also lead you to some very complicated areas of study. For more information I highly recommend William Lane Craig’s Reasonable Faith. Dr. Craig is also has a plethora of information on his website.