A persistent argument commonly used by theists to support their claim that a personal god exists invokes the supposed “fine-tuning” of the physical constants in the universe. Natural physical forces alone, so the argument goes, could not possibly have produced an orderly universe that sustains life. The values of several physical constants are such that, if they were even slightly different, life as we know it would be impossible. The argument invokes a supernatural directing hand to account for the fact that life, the universe, and everything beat astronomical odds by coming into existence.
It is certainly true that life as we know it owes its existence to the values of several physical constants being set exactly as they are. But “life as we know it” is an important qualifier. It does not follow that no plausible forms of life could have existed under the hair-trigger circumstances that resulted in the physical constants being just right. This was demonstrated by the late particle physicist Victor Stenger, who wrote a computer program in the early 1990s called “MonkeyGod.” This program is an interactive module that allows the user to design and run a model universe, simply by changing the values of however many constants the user sees fit and then seeing what kind of virtual universe emerges. Stenger writes, “While these are really only ‘toy’ universes, the exercise illustrates that many different universes are possible, even within the existing laws of physics.”  Stenger reports on his own experiments with the program as follows:
In previous publications, I have applied MonkeyGod in a computer simulation in which I varied the four parameters randomly (on a logarithmic scale) over ten orders of magnitude. I was mainly interested in seeing how many universes would have stellar lifetimes long enough to allow for some form of life, not necessarily exactly like ours, to evolve.
. . . I used a formula obtained from one reference for the minimum lifetime of a main sequence star. I later adopted a different formula, from another reference, which I thought was more realistic since it gave the maximum lifetime of a star . . . The results are not in general disagreement with that previously published. In fact, as expected, I get results even more favorable to life. While a few stellar lifetimes are low, most are over ten billion years, which is probably enough time for stellar evolution and heavy element nucleosynthesis to occur. Long stellar life may not be the only requirement for biological life, but I have demonstrated that fine-tuning is not necessary to produce a range amenable for life. 
The random, unplanned, and chaotic emergence of a universe capable of sustaining some kind of life is not as unlikely as most people think. A number of other published studies have reported on computer simulation programs more sophisticated than MonkeyGod, studies which support Stenger’s conclusions. In fact, the scientific evidence strongly suggests that some form of life may have been possible under a range of circumstances different from and wider than those that actually obtained. 
Aside from the scientific problems, the fine-tuning argument also comes up against serious philosophical obstacles. If the God of theism was perfectly omnipotent, why would he need to “fine-tune” the universe for life in the first place? Any universe created by an all-powerful god should be capable of producing and sustaining regardless of what conditions are in place. If, as the theists claim, humanity was special, enjoying a privileged and elevated status above that of all other species by virtue of being formed in the “image of God,” we should be able to live and thrive in literally any locale, under any condition whatever. Why, then, do we humans require life-preserving equipment in order to travel into the void of space? Isn’t the universe supposed to be made for us according to the fine-tuning argument?
The fact of the matter is that we do not know exactly what kind of universe might be possible under a different set of constants. Science is an empirical discipline, and the totality of our collective experience is based on only a single universe: the one we find ourselves inhabiting. Still, as we have seen, it is certainly possible to infer what kind of phenomena might manifest in an alternate universe, one with a different set of physical laws and constants. There are no grounds for concluding that this universe is special in any way.
The universe is not fine-tuned for humanity. Rather, humanity is fine-tuned to the universe. As a species, we humans happened to evolve in the kind of universe that makes our existence possible. If we were not suited for the world in which we find ourselves, we would not be here. The physical circumstances that produced life included Earth having an atmosphere transparent to that extremely narrow region of the electromagnetic spectrum that we call “visible light.” A great deal of the light produced by our sun falls within that region, so it was only natural that evolution developed the human eye the way it did. It is absurd to argue that the reason the Sun produces light within a spectrum to which Earth’s atmosphere happens to be transparent is because human eyes are sensitive only to that region. But this is exactly the kind of silly reasoning that underlies the ostensibly “scientific” fine-tuning argument for God.
There is nothing enigmatic, mysterious, or anomalous about the presence of finely-constrained order in the universe. An example of a real anomaly that would constitute evidence of a supernatural force controlling nature would be a radical and drastic alteration of physical law occurring before our eyes – in other words, a bona fide miracle. There has never been any verified and independently-corroborated documentation of such an event ever happening. The actual state of the universe at any given moment is the inevitable and unavoidable natural result of all the innumerable physical conditions that prevail. And these natural physical conditions, which have come to be very well-understood by physicists and cosmologists, did not need any help from an outside creative agent. Regardless of what the “real” nature of our admittedly provisional models of physical forces may be, these forces are alone fully capable of producing a universe such as the one we happen to find ourselves inhabiting.
But even if natural physical processes are not alone capable of bringing a universe into existence (they are), what is the mechanism by which a Supernatural Mathematician installs this capacity in natural forces in the first place? No amount of outside engineering direction and intervention could have endowed the so-called “laws” of nature with any more universe-producing capacity than they already possess on their own. Positing the need for an added kick to get things started is to posit a violation of the second law of thermodynamics.
Indeed, if a supernatural creative agent did exist, why should there even be laws of thermodynamics? Such a being could simply create the universe ex nihilo, without needing to take the circuitous route of creating natural elements or forces at all. The Bible itself views an immaterial existence as the ideal state of a theistic universe: “And night shall be no more; they need no light of lamp or sun, for the Lord God will be their light” (Revelation 22:5). If there is a god like this, why did he choose to create photons whose speed is limited by physical law? Why build us to be material bodies that are constrained by physical law? Being supposedly omnipotent and not subject to any law higher than himself, this god could have created us as disembodied minds, spirit beings unbound by any physical law.
We have again come back to the question posed above: If the omnipotent Creator God of the theists really does exist, why should there be any physical constants in need of divine tweaking and adjusting in the first place? In answering this challenge, theists who favor the fine-tuning argument implicitly or explicitly maintain that some divine reason or rationale underlies the natural laws. For example, some theists talk about God using the laws of physics to create “the best of all possible worlds.” But one consequence of this argument is that the supposedly Supreme Being becomes subject to a law over and above himself. The statement “God had a reason and purpose in creating the universe” posits a law external and anterior to divine edicts.
 Victor J. Stenger, The Fallacy of Fine-Tuning: Why the Universe is Not Designed for Us (Amherst, NY: Prometheus Books, 2011), p. 236.
 Ibid, pp. 240-41.
 Fred C. Adams, “Stars in Other Universes: Stellar Structure with Different Fundamental Constants,” Journal of Cosmology and Astroparticle Physics 08 (August 2008); Roni Harnik et al., “A Universe without Weak Interactions,” Physical Review D74 (2006): 035006; Anthony Aguirre, “Cold Big-Bang Cosmology as a Counter Example to Several Anthropic Arguments,” Physical Review D64 (2001): 083508.