Prominent atheist Christopher Hitchens (who has passed away recently) called the fine-tuning argument the most intriguing argument for the existence of a Creator, (http://www.youtube.com/watch?v=wSYKwAxyOG0). While Hitchens was stubborn, hardheaded, and often unreasonable in my personal opinion, I have to admire him for being vulnerable and admitting that this isn’t a topic that should be easily dismissed. It takes a lot of courage to admit a weakness in one’s own stance, especially when you’ve published on!
1) The fine-tuning of the universe is due to either physical necessity, chance, or design
2) It is not due to physical necessity or chance
3) Therefore, it is due to design.
Now, let’s address how the universe cannot be a product of physical necessity or chance in order to identify how we come up with the conclusion that the universe is designed.
The first option for the fine-tuning of the universe is physical necessity. The physical necessity option requires that the universe must have the required constants and quantities in order to produce a life-permitting universe. This would also imply that a life-prohibiting universe would be impossible 1. The fact is that the constants and quantities are not products of the laws of nature and there is no reason to believe they couldn’t be different 2. As of today, there is no empirical evidence to support the claim that the constants and quantities of universe couldn’t have been different. Therefore, the first option of physical necessity is an implausible one.
The second option for the fine-tuning of the universe is chance. That is to say, it was the luck of the draw that all the constants and quantities accidently fell into a life-permitting range. I’ll start off with an analogy. Suppose that you were dragged in front of one hundred trained marksmen for your execution and they were all commanded to simultaneously shoot you. “Ready, aim, FIRE!” is shouted to the marksmen but you remain alive and you notice that every single marksman had missed! Would this enormous improbability lead you to the conclusion that it was mere chance that every single trained marksman had missed? None of us would conclude that every single marksman would have missed by mere accident. The same principles of evaluation apply to the universe. The fact is that the constants and quantities that govern the universe are set perfectly to allow for a life-permitting universe and the probability that every single one fell within the perfect life permitting range is incomprehensibly improbable 1.
Since physical-necessity and chance are not viable options to explain the fine-tuning, it follows logically that design is the best explanation for the fine tuning of the universe. The fact is that if it appears designed, it likely is.
1 William Lane Craig, Reasonable Faith (Wheaton, IL: Crossway Books) Chapter 4
2 William Lane Craig, On Guard (Colorado Springs, CO: David C. Cook) Chapter 5