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The Fine-Tuning Argument for God

The fine-tuning of the universe can't be just a coincidence, so it has to be the work of a designer

Trent Horn

Critics of the design argument—that a higher power intentionally conceived of and created the universe from nothing—have used the theory of evolution to argue that over billions of years, life was able to evolve from a single cell (which also formed through natural processes) into the complex organisms we see today. These critics claim that evolution makes God unnecessary and that life and the apparent design we observe in the universe can be explained naturally.

But design arguments do not need to disprove evolution in order to show that God exists. In fact, many major religions (including Catholicism) hold that religious doctrine and the theory of evolution do not lead to contradictions. Far from needing to disprove evolution, the fine-tuning argument asks, “Why do we live in a universe where evolution is even possible?”

The argument goes like this:

P1. The universe possesses finely tuned physical constants and initial conditions that allow intelligent life to exist.

P2. This is due to necessity, chance, or design.

P3. It was not due to necessity or chance.

C. Therefore, the fine-tuning of the universe is the work of a designer.

Constants are letters in scientific equations that represent unchanging numbers. For example, the C in the formula E=MC2 is a constant referring to the speed of light (approximately 186,000 miles per second). Conditions refer to the amount of matter and energy that was present at the beginning of the universe. The fine-tuning argument asks why these conditions were at the optimal level to allow the evolution of intelligent life.

For example, the cosmological constant represents the strength of gravity in an empty vacuum of space. This constant also controls how fast the universe expands. Once thought to be zero, this constant is actually fine-tuned to the negative 120th power—a decimal point followed by 119 zeroes and a one. And in the past fifty years, scientists have discovered that even a slight variation in many of the laws of nature, including this constant, would have spelled disaster for life as we know it. So there needs to be an explanation for the constant’s incredibly small yet non-zero value.

Even many non-religious scientists agree with the truth of the fine-tuning argument’s first premise, even if they don’t believe that God is the reason for that fine-tuning. Renowned physicist Alexander Vilenkin writes:

A tiny deviation from the required power results in a cosmological disaster, such as the fireball collapsing under its own weight or the universe being nearly empty. . . . This is the most notorious and perplexing case of fine-tuning in physics.

String theorist Leonard Susskind, a non-religious scientist like Vilenkin, says that unless this constant was fine-tuned, “statistically miraculous events” would be needed for our universe to be life-permitting. He suggests that, in light of this, “it is possible that an unknown agent set the early conditions of the universe we observe today.”

Another similar example is the relative weakness of gravitational force. Although gravity may seem like a strong force because it holds all of us on the earth, in comparison to the other forces in nature, it is actually extremely weak. According to Martin Rees, gravity is 1036 times weaker than competing forces within atoms. As a 2009 article in New Scientist magazine put it, “The feebleness of gravity is something we should be grateful for. If it were a tiny bit stronger, none of us would be here to scoff at its puny nature.”

According to some atheists, saying the universe is fine-tuned for life is like saying the Sahara desert is fine-tuned for water. However, to say the universe is fine-tuned for life does not mean that it is a perfect place for the maximum amount of life to evolve. Fine-tuning means only that out of all the possible universes, it is much more likely that there should be no life at all. The fact that our universe does accommodate life, regardless of how little, against such incredible odds requires an explanation.

But what about premise two? Why should we discount both necessity and chance to explain fine-tuning?

First, there is no evidence that the laws of nature or the values of the constants in physics are fixed, and there is some evidence that they are contingent, because we can at least imagine a universe where the constants are different. If the critic claims that these constants have to be the way they are, then he must offer evidence to support that claim.

Far from claiming necessity, scientists who work in a special branch of theoretical physics called string theory believe there are up to 10500 different possible universes that could have formed with different physical constants. Even Richard Dawkins finds the explanation of necessity insufficient:

It is indeed perfectly plausible that there is only one way for a universe to be. But why did that one way have to be such a set-up for our eventual evolution? Why did it have to be the kind of universe which seems almost as if, in the words of the theoretical physicist Freeman Dyson, it “must have known we were coming”?

Other atheists say we shouldn’t be surprised the universe is fine-tuned for life because, if it weren’t, then we wouldn’t be here to appreciate that fact. But, to borrow an example from John Leslie, that would be like saying I shouldn’t be surprised that fifty trained marksmen shot at me and all of them missed, because if even one of them had killed me, then I wouldn’t be here to appreciate that fact.

This so-called anthropic principle explains why we don’t observe life-prohibiting universes (because we’d be non-existent), but it doesn’t explain why we observe such an incredibly unlikely life-permitting universe.

What about fine-tuning being an incredibly fortuitous chance event? Consider this analogy: imagine that you are playing poker with a friend, and he gets a royal flush. You don’t question his apparent luck—until he wins ten hands in a row, all with royal flushes. Now you think he must be cheating, because that explanation is more probable than luck.

Well, the odds of our universe just happening to be finely tuned would be comparable to the odds of getting fifty royal flushes in a row! If we reject chance as an explanation for an improbable poker game, shouldn’t we reject chance as an explanation for an even more improbable universe?*

One last objection is that the fine-tuning argument shows only that the universe was designed, not that the designer is God. However, this is an objection only to an inference derived from the argument’s validly established conclusion. The fine-tuning argument may not prove that a being with every divine attribute created the universe, but it does prove that a powerful being did this—so it forms part of a powerful cumulative case for God’s existence.

For more resources on this argument and how it provides evidence for the existence of God, I recommend my book Answering Atheism; William Lane Craig’s Reasonable Faith; and, for a more comprehensive treatment, Luke Barnes’s excellent book A Fortunate Universe: Life in a Finely Tuned Cosmos. It’s also featured in my course Creation: Out of Nothing? at the Catholic Answers School of Apologetics.


*At this point some critics appeal to the multiverse as a means to overcome this improbability. I addressed this in my book Answering Atheism and may address it in a future article on this subject. For now, this article by my colleague Jimmy Akin may be helpful when it comes to addressing the subject.

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