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What You Missed About the Fine-Tuning Argument

Atheists and Christians who debate the fine-tuning argument for God's existence can fall victim to misunderstandings.

Trent Horn

One popular argument for the existence of God is the fine-tuning argument. This is a version of the design or teleological argument for God’s existence, based on findings made cosmology and astrophysics over the past fifty years.

Since the 1970s, cosmologists and other physicists have confirmed that the strength of gravity between objects lies within a narrow life-permitting range of possible values. Martin Rees, the British royal astronomer, says the odds that it would fall within a life-permitting range are 1 in 1060. The same is true of the strength of gravity in a vacuum devoid of particles, which is called the cosmological constant, and the odds of that constant falling within the life-permitting range are 1 in 10120.

And it’s not just gravity. Similar fine-tuning has been discovered for the strong nuclear force, the weak force, and the low amount of entropy that was present in the universe after the Big Bang. To put these numbers into perspective, the number of atoms in the observable universe is estimated to be 1080. So the odds of getting even one of these constants right is on par with the odds of finding a randomly marked atom somewhere in the visible universe.

Given these facts, some apologists put forward the following version of the fine-tuning argument (FTA) for God’s existence:

  1. The values of the constants in the laws of physics and the conditions of the early universe are fine-tuned.
  2. This fine-tuning is due to necessity, chance, or design.
  3. It is not due to necessity or chance.
  4. Therefore, it is due to design.

Many popular objections to the first premise of the FTA are rooted in a misunderstanding of “fine-tuning.” Normally when we speak of a musical instrument or electronic device being “finely tuned,” we mean that an intelligent agent has adjusted it so that it produces the highest-quality effects. But in the FTA, saying the constants are “fine-tuned” does not mean an agent has set them to produce the best effect possible. If it did, then the argument would be circular—it would be taking for granted exactly the thing it’s setting out to prove. Instead, fine-tuning simply means that the life-permitting values of the constants and conditions is very narrow in comparison to the range of life-prohibiting values. This qualification avoids objections like “the universe is not fine-tuned because 99.99999 percent of it is hostile to of life.”

The first premise of the FTA does not claim that God designed the universe in order to produce the most intelligent embodied life possible. Saying, “God designed the universe for a certain purpose” is a value judgement, whereas the first premise of the FTA is an uncontroversial, empirical judgement. Of all the possible values of the constants and conditions, only a narrow subset of them make it possible for intelligent, embodied life to exist in the universe.

“Fine-tuning” does not mean that an agent has carefully crafted something. Again, if it did, then the argument would be circular. The term is actually neutral to the question of whether an agent or intelligence is involved. According to Barnes and Lewis in their book defending fine-tuning, “whether such a fine-tuner of our universe exists or not, this is not the sense in which we use the term. ‘Fine-tuning’ is a technical term borrowed from physics, and refers to the contrast between a wide range of possibilities and a narrow range of a particular outcome or phenomenon.”

That’s why, in order for the argument to be successful, we need to talk about fine-tuned constants in the laws of nature. And by that we mean that the range of possible values for these constants is large and mostly life-prohibiting. The range for them being life-permitting is much, much smaller. Therefore, the fact that they are life-permitting is an example of fine-tuning, given all the many more possible ways they could have not had that property.

For example, imagine that in the future, with amazing scientific tools, we explored a billion planets and proved that none of them had organic life. Then we find one planet that has a tiny amount of organic life. Naturally, we would ask why this planet is different from all the others. We’d probably discover that the planet had just the right values for things that allow any life to exist, like its size, its orbit, its distance from a star, its possession of a magnetic field, etc. These values would have to be very wide in order for a billion other planets to have values that fall outside this finely tuned range. As a result, scientists would conclude that this planet’s characteristics were fine-tuned to allow life to exist.

You couldn’t disprove the claim that this planet was fine-tuned by simply saying, “But it barely has any life at all!” The fact that it has life, and billions of other planets don’t, requires an explanation, and that explanation is found in the planet having just the right values to support any life. In the same way, the fact that our universe has life in it—and not just billions, but countlessly exponential numbers of other possible universe would not have life—requires an explanation. That explanation is found in our universe having just the right values in the constants of the laws of physics to support any life.

But why do they have these values? Now we are in a good position to investigate whether they must have these values (i.e., necessity), they have them by chance, or they have been designed . . . by the creator of the universe.

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