The Kalam Cosmological Argument
1) If something begins to exist, it must have a cause.
2) The universe began to exist.
Therefore,
3) The universe had a cause
This was the first argument for God that I encountered and, still today, remains one of my favorites. Its current formulation was developed and made famous by the contemporary philosopher and theologian Dr. William Lane Craig, but the argument itself has a history spanning nearly a millennium and originates with philosopher Al-Ghazali. The argument is simple and intuitive. The structure of the argument is that of the logical rule of inference, Modus Ponens. However, the strength of the argument depends upon the plausibility of each of the premises. If premises 1 & 2 are more plausibly true than false, then the conclusion (3) follows necessarily.
Premise 1: If something begins to exist, it must have a cause.
This premise is supported by two philosophical principles: A) the principle of sufficient reason and B) the general principle of causation.
A) The principle of sufficient reason states: that for every fact F there must be a sufficient reason why F is the case. With regard to Premise 1, it simply means that if something exists, it demands an explanation of its existence.
B) The general principle of causation simply states: that for every event b it must have a cause a. The Kalam Cosmological Argument, however, makes a more modest claim: that whatever begins to exist must have a cause. In short, it means that things don't just "pop" into existence without a cause.
Philosopher Walter Terrence Stace once remarked that, "Every student of logic knows that this is the ultimate canon of the sciences, the foundation of them all. If we did not believe in the truth of the law of causation, namely, that everything which has a beginning has a cause,…all the sciences would at once crumble to dust. In every scientific investigation, this truth is assumed”.
Science depends upon the principle of causation. If things could just pop into existence without a cause, it would become inexplicable why anything and everything doesn't just pop into existence without a cause. Rejecting the principle of causation would destroy the scientific endeavor, whose aim is, in large part, a search for causes in an effort to provide an explanation for some phenomena. Philosopher William Lane Craig once mused, "to believe that something could just pop into existence, uncaused, out of nothing, would literally be worse than magic".
Premise 1, then, stands on solid ground as the one premise that is universally verified and never falsified and, therefore, more plausibly true than false.
Premise 2: The universe began to exist
This premise is supported by both philosophical and scientific evidence.
The philosophical evidence:
1) The impossibility of traversing an actual infinite series of past events. This means that the history of the universe cannot be eternal in the past. Consider the following simple thought experiment:
a) You have a series of dominos laying in front of you and each one represents a moment in time. They stretch to the left for infinity into the past. The one directly in front of you represents today. But, before you get to today, the domino prior must fall over, but before you get to that domino, the domino before it must fall over and the one before that one must fall over, so on and so forth forever into infinity. In effect, you would never arrive at today because there would be an infinite series of past events that have to occur first. So, the fact that we are at today is good evidence that the universe must have a beginning in time.
2) The absurdity of an actual infinite number of things.
b) "Hilbert's Hotel" is a famous example of the absurdity of an "actual infinite". A visual explanation is given in the "Part 2: Philosophical" video below as well as other examples.
The scientific evidence:
1) The Second Law of Thermodynamics: Entropy is always increasing. Entropy is the measure of disorder in the universe. In the most basic sense, entropy stipulates that things fall apart, decay, and energy transforms from usable to unusable energy. As time goes on, the amount of usable energy decreases while the amount of unusable energy in the universe continues to increase. However, if the universe has existed forever, we should expect to find a universe completely exhausted of usable energy, but we don't. Not only does this suggests the universe had a beginning, but it also spells the demise of our universe in an eventual "heat death".
2) The Borde-Guth-Vilenkin (BGV) Theorem: The BGV theorem argues that any universe (even the alleged multi-verse) that is, on average, expanding throughout its history cannot be eternal in the past, it must have a cosmic beginning. Alexander Vilenkin, one of the authors of the BGV theorem, writes in his book, "It is said that an argument is what convinces reasonable men and a proof is what it takes to convince even an unreasonable man. With the proof now in place, cosmologists can no longer hide behind the possibility of a past eternal universe. There is no escape, they have to face the problem of a cosmic beginning."
3) Cosmic Microwave Background Radiation (CMBR): This is the remnant heat from the initial creation event. It permeates the entire universe at just 2.73 degrees above absolute zero and serves as the "fingerprints" of the Big Bang.
Premise 2 also seems to be more plausibly true than false.
Conclusion: The Universe Had a Cause
Given that premises 1 & 2 are more plausibly true than false, the conclusion follows necessarily: the universe had a cause.
Further, given the fact that the beginning of the universe also marks the beginning of time, space, and matter, we can conclude that the cause of the universe must, therefore, be timeless, spaceless, and immaterial. It must also be incomprehensively powerful, since it created the universe out of nothing and personal, since it made a willful decision to create the universe.
In effect, we have a timeless, spaceless, immaterial, incomprehensibly powerful, personal, creator of the universe. These characteristics are typically what we mean by God.