Question: "What is the fine-tuning argument?"
Answer: The fine-tuning argument is a specific application of the teleological argument for the existence of God. A teleological argument seeks to demonstrate that the appearance of purpose or design is itself evidence of a designer. The counter to such a claim suggests that what “appears” to be designed is simply random coincidence. The counter to that counter, so to speak, notes the drastic improbability of certain things being accidental. Fine-tuning arguments tend to focus on the specific nature of the universe and how it appears to have been carefully arranged to allow for intelligent life.
Modern physics recognizes a set of universal constants. These fundamental quantities are entirely independent: they are not derived from anything else. Properties such as the strength of steel or the rate of heat transfer through glass are dependent: they are effects caused by a combination of other factors. Independent constants such as the elementary charge of a proton, the Planck constant, or the speed of light in a vacuum are not the result of other forces or effects. They are “hard-coded” at the most fundamental levels of reality. Modern science currently recognizes more than twenty of these constants.
Fine-tuning arguments look at these and other factors that influence the nature of the universe. According to the fine-tuning argument, the exact quantity of each physical constant and the respective ratios must all be precisely as they are in order for life to exist. In most cases, the tiniest change to one of these constants would not only prohibit life as we know it, but it would make most forms of matter impossible, as well. Our universe is not merely tuned to allow for “some kind” of life, but it seems to be arranged in the only way allowing for “any life” at all.
The probabilities involved with the fine-tuning of the universe aren’t comparable to winning the lottery or being struck by lightning. Lottery odds are represented using eight or nine digits, e.g., 1:109. Randomly dealing a deck of 52 playing cards in perfect order presents odds of 1:1068. Physicists express the odds of “randomly” arranging universal physical constants in the present arrangement using numbers more like 1:10120.
In that sense, a universe capable of sustaining intelligent life is like a treasure hidden in safe whose dial has millions of numbers and whose proper combination is millions of digits long. A single wrong digit, anywhere, and there is no result. It can’t be partly opened, or mostly opened—the door is entirely closed unless the combination is perfect.
If someone opened that million-digit lock, it would be overwhelmingly likely they did so on purpose. Immediately dismissing the feat as random chance would be inane. Lacking any evidence that the person repeated random digits until the safe opened—just as we lack any evidence whatsoever for a cyclical universe or parallel realities—the most sensible conclusion is “fine-tuning.”
Fine-tuning points to specific properties of the universe and posits that some higher power deliberately chose their arrangement. This is grounded in a reasonable assumption, based on the evidence at hand. Of course, as with the cosmological argument, the fine-tuning argument gives little information about the nature of the “Fine-tuner.” That subject must be explored through other means.