Theists argue that the fine-tuning of the physical constants of the universe provide evidence that the universe is designed.  For example, if gravitational force was 1/100,000,000,000,000th (1/100 trillionth) degree stronger the universe would not have expanded to form the terrestrial bodies.  If the force was 1/100,000,000,000,000th degree weaker the universe would expand at rate too fast for matter to coalesce into terrestrial bodies.  The ratio of electrons to protons is fine-tuned to 1 part in 1037, meaning if the ratio was altered by just 1 part in 10,000,000,000,000,000,000,000,000,000,
000,000,000 complex life would not be possible.

To give you a sense of the specificity involved, Hugh Ross asks us to imagine covering the entire North American continent with dimes, all the way up to the moon (239,000 miles high).  Do the same thing on 1,000,000,000 other continents of identical size, “[p]aint one dime red and mix it into the billion of piles of dimes.  Blindfold a friend and ask him to pick out one dime.  The odds that he will pick the red dime are one in 1037.”[1]

This is just one of many finely-tuned constants.  Indeed, it is one of the less-specified constants.  The cosmological constant (governs the expansion rate of the universe) is fine-tuned to 1 part in 10120!  We reason that of all the possible values the constants could have assumed, it is unfathomably improbable that they assumed the extremely narrow range of life-permitting values they have by chance alone.  If chance cannot account for their precise values, then their values must have been determined by a designing intelligence (which most would identify as God).

Atheists admit that the universe is finely-tuned for the existence of complex life, but deny that God is the best explanation for why the physical constants have the values they do.  They attempt to undercut the argument for theism from fine-tuning by saying we lack sufficient justification for thinking the constants could have assumed values different from what they have.  It could be that they possess these values necessarily out of some physical necessity similar to the way the sum of the angles of a triangle must be 180 degrees.  If so, then while the constants themselves may be contingent beings, their values are necessary such that whenever physical constants come into being they must assume the values we observe them to have.  If so, no fine-tuner is necessary to explain them.  So long as it’s possible that value of the constants is necessary, we are not justified in drawing a design inference.

Two things should be noted.  First, even if the atheist’s rebuttal is successful, it does not prove that God does not exist.  In fact, it does not even prove that the physical constants are not fine-tuned by a designing intelligence.[2]  It only shows that the cogency of the argument is commensurate with the degree of confidence we have that the values of the physical constants are contingent rather than necessary.  If we can only be 30% confident that they are contingent, then we can only be 30% confident in the argument’s conclusion.  Likewise, if we can be 90% confident that they are contingent, then we can be 90% confident in the argument’s conclusion.  The real question, then, is what reasons exist for thinking the values are necessary rather than contingent.  The mere logical possibility that they could be necessary is not enough.  Possibilities come cheap.  The atheist must demonstrate that the reasons for thinking the values to be necessary are so compelling that they should render our confidence in the idea that their value is contingent to >50%.  Unfortunately, atheists have not provided any reasons for thinking the values to be necessary (they seem to think raising the mere possibility is enough to undercut our argument); therefore, we have no reason for doubting that the values are contingent.[3]

Secondly, there is good reason to think it’s impossible for the values to be necessary.  The nature of a thing that comes into being can only be determined by the thing that brings it into existence.  If the universe sprang into existence from absolutely nothing, then there were no physical, metaphysical, or logical entities to determine what came into existence.  If we start with nothing, then it is just as probable that a universe with our precise physical constants pop into existence as it is that a universe with different physical constants, or even a piece of cheese pop into existence!  If something could pop into existence from nothing, then anything and everything could pop into existence from nothing, including constants with different values than the values our physical constants have assumed.  There is no basis for the materialist claim, then, that the physical constants of our universe may be necessary.  The design argument stands.

[1]Hugh Ross, The Creator and the Cosmos, 115.
It is an undercutting defeater rather than a rebutting defeater, meaning that it only serves to show that the conclusion to the argument lacks warrant—not that it is false.
One might counter that necessity, not contingency, is the default position; i.e. unless we have good reason to believe the values of the constants are contingent, we should understand them to be necessary.  This response will not do.  On the basis of probability alone, contingency ought to be our default position.  Everything we encounter in the universe is contingent, and thus it is more probable than not that the values of the physical constants are contingent as well.  If the constants are physically necessary, they would be the only examples of physical necessity in the entire universe.  Given such uniqueness, there is no justification for thinking that they are necessary apart from good evidence.  No evidence has been offered.  Indeed, it seems that such evidence would be impossible to obtain.

Philosophically speaking the evidence is opposed to the notion.  One of the requirements of a necessary being is that it is eternal.  The universe began to exist in the finite past, and thus the physical constants are not eternal.  And if they are not eternal, they cannot be necessary.  One could seek to avoid this conclusion by identifying the physical constants with abstract objects that exist eternally in some sort of Platonic realm, but then they need to explain how causally impotent abstract objects are causally related to the physical world.