Ganssle begins by acknowledging the difficulty of defining "naturalism." Naturalism "involves both claims about the kinds of things that exist and commitments to a certain methodology... it is possible to take naturalism either as consisting more fundamentally in a claim about what exists, or as consisting more basically in a commitment to certain methods."
Naturalism as a claim ("claim naturalism") says: ‘Naturalism is most fundamentally the claim that the only kinds of things that exist are natural things. No supernatural or transcendent entities or processes exist. ’
Naturalism as a commitment to methodologies ("method naturalism") says: ‘Naturalism is most fundamentally a commitment to hold that whatever (and only whatever) the proper use of scientific methods leads us to believe about the world, in the long run, is what we ought to believe about the world.’ Method naturalism is different than "methodological naturalism" ( "the position that one ought to adopt claim naturalism as a working assumption when doing science, whether or not one believes claim naturalism to be true.")
After defining these terms Ganssle turns to the fine-tuning argument (FTA) for God's existence. This is, arguably , "the most popular version of theistic argumentn in contemporary philosophy of religion." It is a kind of design argument that avoids neo-Darwinian challenges to the traditional, William Paley-type teleological argument.
The facts the FTA appeals to are not disputed. Ganssle quotes Daniel Dennett:
"As more and more has been learned about the development of the universe since the Big Bang, about the conditions that permitted the formation of galaxies and stars and the heavy elements from which planets can be formed, physicists and cosmologists have been more and more struck by the exquisite sensitivity of the laws of nature. The speed of light is approximately 186,000 miles per second. What if it were only 185,000 miles per second, or 187,000 miles per second? Would that change much of anything? What if the force of gravity were 1 percent more or less than it is ? The fundamental constants of physics- the speed of light, the constant of gravitational attraction, the weak and strong forces of subatomic interaction, Planck’s constant – have values that of course permit the actual development of the universe as we know it to have happened. But it turns out that if in imagination we change any of these values by just the tiniest amount, we thereby posit a universe in which none of this could have happened, and indeed in which apparently nothing life-like could ever have emerged: no planets, no atmospheres, no solids at all, no elements except hydrogen and helium, or maybe not even that- just some boring plasma of hot, undifferentiated stuff, or an equally boring nothingness. So, isn’t it a wonderful fact that the laws are just right for us to exist? Indeed, one might want to add, we almost didn’t make it!"
Ganssle next discusses the FTA in relation to claim naturalism. "Claim naturalism is that it straightforwardly captures our pre-theoretical intuitions about what naturalism ought to be. The opposite of naturalism is supernaturalism. A naturalist, then, does not think that any supernatural things exist. Naturalism, in this way, has been closely allied with materialism and physicalism."
What qualifies something as "natural," and as "supernatural?" The claim naturalist may here appeal to science. But if science provides "the only or the most precise criterion for what counts as natural, then the natural/non-natural distinction can be only as sharp as the science/non-science distinction. If the distinction between what is genuine science and what is not is vague, the line between what is natural and what is not will be similarly vague. If science cannot be precisely demarcated, neither can naturalism."
Science, thinks Ganssle, cannot be precisely demarcated. In itself this is no big deal. But it becomes a big deal "if there is an ontological claim tied to the results of science." And "claim naturalism is an ontological claim. The only things that exist are those things that can be discovered or understood by application of scientific methodologies." Since what counts as science and what does not is vague, it will therefore be impossible to precisely demarcate the "natural" from the supposed "supernatural."
So, one difficulty for "claim naturalism" is: because the boundaries of what is science and what is not science are vague, and if science determines what is natural, then, strictly speaking, determining what is or is not natural will be impossible.
The FTA itself presents another difficulty for claim naturalism. "Obviously, if the argument makes it reasonable to think that a designer of the universe exists, then it supports the conclusion that claim naturalism is false. God, if He exists, is the clearest possible example of a supernatural entity."
OK. BUt at this point the best or most popular response the claim naturalist will take is to put forth the "many-worlds hypothesis." Ganssle says: If the many-worlds hypothesis is true or well-supported, the inference to purpose and therefore a designer is undermined considerably." (Note: here Robin Collins and William Lane Craig, e.g., would disagree that the existence of a multiverse essentially changes the FTA.)
Ganssle wants to show that the many-worlds hypothesis, if true, will make the going tough for the claim naturalist. He writes: "The cost of thinking that the many-worlds hypothesis is true is that one must hold that there actually exists (or did exist) a vast quantity of worlds or universes. These worlds are odd entities for naturalists to believe in. To be sure, the many universes do not show up on anyone’s pretheoretical list of supernatural (or non-natural) items. As a result, they do not seem at first glance to be non-natural. A good case can be made, however, that they are non-natural indeed."
Ahhh... now this is interesting! And new, I think. How are the posited "many universes" non-natural?
"First, none of the other worlds are causally accessible to us. Most of them will have collapsed nearly immediately or expanded too quickly to allow star formation. The few that are stable are outside our space-time universe and causally disconnected from our universe. Therefore, they are outside of our empirical epistemic range."
We cannot have epistemic access to verify them empirically, not because they are hard to find, "but because they cannot be found" (in principle). "It is physically impossible that we could get any empirical information from any cosmos but our own." (This objection to claim naturalism is not new. For example, Betty and Cordell made it back in the mid-80s.)
Second, "the laws of physics in these worlds, if there are any laws at all, are different from the laws in our own universe. If the methods of science involve explanation by appeal to physical laws that are in continuity with those we have discovered, then the many universes fall outside those methods." Ganssle's point is this. If science (as we understand it) determines what or what not qualifies as "natural," and if the physical laws of other universes are different from our own, then our "science" will not necessarily or at all apply in such other universes. Therefore it is quite a stretch to think that "science" (as we understand it) defines what is "natural" and potentially "supernatural." Ganssle writes: It is a matter of conceptual necessity, however, that nearly every one of the various universes has different laws of nature, if they have any at all. As a result, the kinds and properties of objects that exist will differ widely from cosmos to cosmos. These differences indicate that it is quite a stretch to think that the many-worlds hypothesis postulates only entities of the sort approved by the methods of science."
"The FTA provides a significant challenge to claim naturalism. The evidence for fine tuning supports the claim that either a designer/creator exists or that a vast array of other universes exists. In either case, the evidence supports the existence of things that are not naturalistic. Therefore, naturalism, as a claim about what exists, faces significant counter-evidence."
