This is the second installment of my blog series "Mapping the Fine-Tuning Argument" in which I try to give a simple, common-sense breakdown of the argument.
The idea behind it is this: Physicists know what numbers that they should plug in to their equations to describe certain physical laws and forces. But no one knows why our universe had to have the numbers it does and not some other numbers. For example, why does light have to travel at 186,000 miles per second rather than 200,000 miles per second or 50,000 miles per second (or any other number we can imagine)? What's more is that, when physicists change some of the numbers that they use in their equations (even to a very small degree), it appears that the universe described in their equations would not support life as we know it. It seems that out of all the logically possible universes, very few would support life (as we know it, anyway). How do we explain that? Many believers argue that God is the explanation. I suppose they believe that God would have wanted life to exist, and so if God exists there is a 100% chance that our universe will exist with all the laws of physics having values that will allow life to exist. However, if chance is behind the laws of the universe, then our existence would be very, very improbable. Of course, many will object that chance is not the only alternative to God, and they are right. In later blog posts I will discuss the alternatives. But for now, suffice it to say that believers tend to argue that the alternative explanations are contrived or in some way not as good as the theisitic explanation.