|Bolles Harbor, Monroe|
In my MCCC Philosophy of Religion I'm now presenting the last argument in section 1 of our class, which is: the fine-tuning argument for the existence of God. In section 2 we'll look at what is, arguably, the main atheistic argument against God's existence; viz., the argument from evil. Note: there aren't a lot of philosophical arguments against God's existence.
I'm using Robin Collins's version of the argument, which is:
1. The existence of the fine-tuned universe is not improbable under theism.
2. The existence of the fine-tuned universe is very improbable under the atheistic single-universe hypothesis.
3. Therefore, given 1 and 2 and the prime principle of confirmation (aka inference to the best explanation), theism is more probable than atheism.
When atheists were confronted with the reality that our universe is fine-tuned for life, some of them, in order to evade the obvious conclusion of theism, posited a "multiverse." "If all of these other universes really exist, then by chance alone life-permitting worlds will appear somewhere in the world ensemble." (William Lane Craig, On Guard, 117)
How do we respond to the many worlds hypothesis? Following Craig, we have at least three responses. Note that Craig's first two responses do not object to the existence of a multiverse.
Response #1 to the many worlds hypothesis
The multiverse itself also involves fine-tuning. "For in order to be scientifically credible, some plausible mechanism must be suggested for generating the many worlds. But if the many worlds hypothesis is to be successful in attributing fine-tuning to chance alone, then the mechanism that generates the many worlds had better not be fine-tuned itself. For if it is, the the problem arises all over again: How do you explain the fine-tuning of the multiverse?" (Ib., 117-118)
Response #2 to the many worlds hypothesis
The Borde-Guth-Vilenkin theorum "requires that even a multiverse of bubble universes must have a beginning. In that case the mechanism that generates the bubble universes has been chugging away for only a finite amount of time. So by now, there may well be only a finite number of bubbles in the world ensemble, which may not be enough to guarantee the appearance of a finely tuned universe by chance alone. There's no evidence that the sort of world ensemble required by the many worlds hypothesis actually exists." (Ib., 118-119)
Response #3 to the many worlds hypothesis
"If our world is just a random member of a world ensemble, then it's vastly more probable that we should be observing a much smaller region of order. It turns out that a parallel problem faces the many worlds hypothesis as an explanation of fine-tuning. [Oxford physicist] Roger Penrose has pressed this objection forcefully." (Ib., 119) Penrose's objection may, writes Craig, be "devastating" to multiverse theory.
ROBIN COLLINS'S RESPONSE TO MULTIVERSE THEORY
(This is especially for my MCCC Philosophy of Religion students. Here is Robin Collins's [PhD in physics] response, quoted in full, to the multiverse theory objection. For Collins's paper, go here; scroll down to "God, Design, and Fine-tuning." Note that Collins does not object to the idea of a multiverse.)
One major theistic response to the many-universes generator scenario, whether of the inflationary variety or some other type, is that a “many-universes generator” would seem to need to be “well-designed” in order to produce life-sustaining universes. After all, even a mundane item like a bread machine, which only produces loaves of bread instead of universes, must be well designed to produce decent loaves of bread. If this is right, then invoking some sort of many-universes generator as an explanation of the fine-tuning only kicks the issue of design up one level, to the question of who designed the many-universes generator.
The inflationary scenario discussed above is a good test case of this line of reasoning. The inflationary/superstring many-universes generator can only produce life-sustaining universes because it has the following “components” or “mechanisms:”
i) A mechanism to supply the energy needed for the bubble universes: This mechanism is the hypothesized inflaton field. By imparting a constant energy density to empty space, as space expands the inflaton field can act “as a reservoir of unlimited energy” for the bubbles (Peacock, 1999, p. 26).
ii) A mechanism to form the bubbles: This mechanism is Einstein’s equation of general relativity. Because of its peculiar form, Einstein’s equation dictates that space expand at an enormous rate in the presence of a field, such as the inflaton field, that imparts a constant (and homogenous) energy density to empty space. This causes both the bubble universes to form and the rapid expansion of the pre-space (the “ocean”) which keeps the bubbles from colliding.
iii) A mechanism to convert the energy of the inflaton field to the normal mass-energy we find in our universe. This mechanism is Einstein’s relation of the equivalence of mass and energy (i.e., E = mc2 ) combined with an hypothesized coupling between the inflaton field and normal mass-energy fields we find in our universe.
iv) A mechanism that allows enough variation in the constants of physics among universes: The most physically viable candidate for this mechanism is superstring theory. As explained above, superstring theory might allow enough variation in the variations in the constants of physics among bubble universes to make it reasonably likely that a fine-tuned universe would be produced. The other leading alternatives to string theory being explored by physicists, such as the currently proposed models for Grand Unified Field Theories (GUTS), do not appear to allow for enough variation. 
Without all these “components,” the many-universes generator would almost certainly fail to produce a single life-sustaining universe. For example, Einstein’s equation and the inflaton field harmoniously work together to enormously inflate small regions of space while at the same time both imparting to them the positive energy density necessary for a universe with significant mass-energy and causing the pre-space to expand rapidly enough to keep the bubble universes from colliding. Without either factor, there would neither be regions of space that inflate nor would those regions have the mass-energy necessary for a universe to exist. If, for example, the universe obeyed
theory of gravity instead of Einstein’s, the vacuum energy of the inflaton
field would at best simply create a gravitational attraction causing space to
contract, not to expand. Thus no
universes would be formed.
In addition to the four factors listed above, the inflationary/superstring many-universes generator can only produce life-sustaining universes because the right background laws are in place. For example, as mentioned earlier, without the principle of quantization, all electrons would be sucked into the atomic nuclei and hence atoms would be impossible; without the Pauli-exclusion principle, electrons would occupy the lowest atomic orbit and hence complex and varied atoms would be impossible; without a universally attractive force between all masses, such as gravity, matter would not be able to form sufficiently large material bodies (such as planets) for life to develop or for long-lived stable energy sources such as stars to exist. 
In sum, even if an inflationary/superstring many-universes generator exists, it along with the background laws and principles could be said to be an irreducibly complex system, to borrow a phrase from biochemist Michael Behe (1996), with just the right combination of laws and fields for the production of life-permitting universes: if one of the components were missing or different, such as Einstein’s equation or the Pauli-exclusion principle, it is unlikely that any life-permitting universes could be produced. In the absence of alternative explanations, the existence of such an a system suggests design since it seems very unlikely that such a system would have just the right components by chance. It does not seem, therefore, that one can escape the conclusion of design merely by hypothesizing some sort of many-universes generator.
Further, the many-universes generator hypothesis cannot explain other features of the universe that seem to exhibit apparent design, whereas theism can. For example, many physicists, such as Albert Einstein, have observed that the basic laws of physics exhibit an extraordinary degree of beauty, elegance, harmony, and ingenuity. Nobel Prize winning physicist Steven Weinberg, for instance, devotes a whole chapter of his book Dreams of a Final Theory (Chapter 6, "Beautiful Theories") explaining how the criteria of beauty and elegance are commonly used to guide physicists in formulating the right laws. Indeed, one of most prominent theoretical physicists of this century, Paul Dirac, went so far as to claim that "it is more important to have beauty in one's equations than to have them fit experiment." (1963, p. 47).
Now such beauty, elegance, and ingenuity make sense if the universe was designed by God. Under the atheistic many-universes hypothesis, however, there is no reason to expect the fundamental laws to be elegant or beautiful. As theoretical physicist Paul Davies writes, "If nature is so 'clever' as to exploit mechanisms that amaze us with their ingenuity, is that not persuasive evidence for the existence of intelligent design behind the universe? If the world's finest minds can unravel only with difficulty the deeper workings of nature, how could it be supposed that those workings are merely a mindless accident, a product of blind chance?"(1984, pp. 235-36.)
Finally, I have argued elsewhere (Collins, “A Theistic Perspective on the Multiverse Hypothesis,” forthcoming) that even if we obtained compelling scientific evidence for such a universe generator, this would pose no threat to theism. Given that God is infinite, and infinitely creative, it makes sense that God would create not only a universe that is vast in both space and time, but perhaps many such universes. Thus, one could argue, theists should welcome such an hypothesis as further illustrating the infinite nature of God.
 The simplest and most studied GUT, SU(5), allows for three differing sets of values for the fundamental constants of physics when the other non-SU(5) Higgs fields are neglected (Linde, PP&IC, p. 33). Including all the other Higgs fields, the number of variations increases to perhaps several dozen (Linde, IQC, p. 6). Merely to account for the fine-tuning of the cosmological constant, however, which is estimated to be fine-tuned to one part in 1053 , would require on the order of 1053 variations of the physical constants among universes.
 Although some of the laws of physics can vary from universe to universe in string theory, these background laws and principles are a result of the structure of string theory and therefore cannot be explained by the inflationary/superstring many-universes hypothesis since they must occur in all universes. Further, since the variation among universes would consist of variation of the masses and types of particles, and the form of the forces between them, complex structures would almost certainly be atom-like and stable energy sources would almost certainly require aggregates of matter. Thus, the above background laws seem necessary for there to be life in any of the many-universes generated in this scenario, not merely a universe with our specific types of particles and forces.