One of the most astonishing discoveries of the twentieth century was that the universe is fine-tuned to support intelligent life. From the force of gravity to the balance of matter and antimatter, the universe is balanced, as it were, on the fine edge of a razor.

Consider the force of gravity. If it were stronger or weaker by just one part out of 10100 (that’s a 1 with one hundred zeros after it!), the universe would not—could not—support intelligent life! To help grasp this number and not miss the gravity of gravity’s fine-tuning, consider that the number of atoms in the entire observable universe is estimated to be only 1080.

Furthermore, the fine-tuning of a force like gravity could not be a function of physical law. Why? Gravity could be stronger or weaker and still be gravity, so physical law does not dictate its precise strength. But were the force of gravity not fine-tuned to be the strength that it is, it could not support intelligent life.

Finally, the fine-tuning of the universe cannot reasonably be attributed to chance because of the infinitesimally small range of values involved. Chance is “infinitely” more likely to produce a life-prohibiting universe than a life-sustaining one. The only plausible source of the fine-tuning of the universe is an external, transcendent, incalculably powerful and intelligent personal Mind, whom we call God.

Source (and for further study), see William Lane Craig, Reasonable Faith: Christian Truth and Apologetics, 3rd ed. (Wheaton, IL: Crossway, 2008).