In this section, I will argue that - even if a multiverse-generator exists -the argument for theism from the fine-tuning of the constants for intelligent life is not completely eliminated. The argument essentially goes as follows. The multiverse-generator itself, whether of the inflationary variety or some other type, seems 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 as an appliance and must have the right ingredients (flour, water and yeast) to produce decent loaves of bread. If this is right, then invoking some sort of multiverse-generator as an explanation of the fine-tuning serves to kick the issue of design up one level, to the question of who designed the multiverse-generator.
The inflationary multiverse scenario, widely considered as the most physically viable, provides a good test case of this line of reasoning. The inflationary multiverse-generator can only produce life-sustaining universes (or regions of spacetime) because it has the following 'components' or 'mechanisms':
(1) A mechanism to supply the energy needed for the bubble universes. This mechanism is the hypothesized inflaton field. By imparting a constant
4 It should be noted, however, that in Leslie's recent book  he argues for a pantheistic conception of God based on this principle and other considerations. In his view, every universe (or reality) whose sum value (both moral and aesthetic) is positive exists as a thought in the mind of God, with our universe itself existing as one such thought. (Like models in a computer simulation, God's thoughts are considered to have substantial structure — and thus substantial existence — in God's mind.) For a short critique of this fascinating book and Leslie's response, see my review essay  and ref. .
energy density to empty space as space expands, the inflaton field can act 'as a reservoir of unlimited energy'  for the bubbles.
(2) A mechanism to form the bubbles. This mechanism relates to Einstein's equations of general relativity. Because of their peculiar form, Einstein's equations dictate that space expands at an enormous rate in the presence of a field - like the inflaton - which imparts a constant (and homogeneous) energy density to empty space. This causes both the formation of the bubble universes and the rapid expansion which keeps them from colliding.
(3) 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 equivalence of mass and energy, combined with an hypothesized coupling between the inflaton field and normal mass/energy fields we find in our universe.
(4) A mechanism that allows enough variation in constants of physics among universes. Currently, the most physically viable candidate for this mechanism is superstring or M-theory. Superstring theory might allow enough variation in the constants of physics among bubble universes to make it reasonably likely that a fine-tuned universe would be produced, but no one knows for sure.5
Without all these 'components', the multiverse-generator would almost certainly fail to produce a single life-sustaining universe. If, for example, the universe obeyed Newton's theory of gravity instead of Einstein's, the vacuum energy of the inflaton field would at best create a gravitational attraction causing space to contract rather than expand.
In addition to the four factors listed above, the inflationary multiverse generator can only produce life-sustaining universes because the right background laws are in place. Specifically, the background laws must be such as to allow the conversion of the mass/energy into the material forms required for the sort of stable complexity needed for life. For example, 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
5 See Leonard Susskind's contribution to this volume  for the variations allowed by superstring theory. The other leading alternatives to string theory being explored by physicists, such as the currently proposed models for Grand Unified Theories (GUTs), do not appear to allow for enough variation. 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 . Including all the other Higgs fields, the number of variations increases to perhaps several dozen . Merely to account for the fine-tuning of the cosmological constant, however, which is estimated to be fine-tuned to be at least one part in 1053, would require on the order of 1053 variations of the physical constants among universes.
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 complex, intelligent life to develop or for long-lived stable energy sources like stars to exist.6
In sum, even if an inflationary multiverse-generator exists, it must involve just the right combination of laws, principles and fields for the production of life-permitting universes; if one of the components were missing or different -such as Einstein's equation or Pauli's exclusion principle - it is unlikely that any life-permitting universes could be produced. In the absence of alternative explanations, it follows from the surprise principle that the existence of such a system could be considered to suggest design since it seems very surprising that such a system would have just the right components as a brute fact, but not surprising under the theistic design hypothesis. Thus, it does not seem that one can completely escape the suggestion of design merely by hypothesizing some sort of multiverse-generator.
It must be admitted, however, that if such a multiverse-generator could be verified, the sort of quantitative evidence for design based on the fine-tuning of the constants would be eliminated. Whereas the degree of fine-tuning of a particular constant of physics could arguably be assigned a number - such as that corresponding to the ratio of the length of its intelligent-life-permitting range to some non-arbitrarily specified 'theoretically possible' range - we cannot provide a quantitative estimate for the degree of apparent design in the cases mentioned above. All we can say is that if certain seemingly highly specific sorts of laws were not in place, no life-sustaining universes could be generated. Thus, depending on the weight one attaches to such quantitative estimates, the evidence for design would be mitigated, although not completely eliminated.
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