A new brand of creationism has appeared on the scene in the last few years. The so-called neocreationists largely do not believe in a young Earth or in a too literal interpretation of the Bible. While still mostly propelled by a religious agenda and financed by mainly Christian sources such as the Templeton Foundation and the Discovery Institute, the intellectual challenge posed by neocreationism is sophisticated enough to require detailed consideration (see Edis 2001; Roche 2001).

Among the chief exponents of Intelligent Design (ID) theory, as this new brand of creationism is called, is William Dembski, a mathematical philosopher and author of The Design Inference (1998a). In that book he attempts to show that there must be an intelligent designer behind natural phenomena such as evolution and the very origin of the universe (see Pigliucci 2000 for a detailed critique). Dembki’s (1998b) argument is that modern science ever since Francis Bacon has illicitly dropped two of Aristotle’s famous four types of causes from consideration altogether, thereby unnecessarily restricting its own explanatory power. Science is thus incomplete, and intelligent design theory will rectify this sorry state of affairs, if only close-minded evolutionists would allow Dembski and company to do the job.

Aristotle’s Four Causes in Science

Aristotle identified material causes, what something is made of; formal causes, the structure of the thing or phenomenon; efficient causes, the immediate activity producing a phenomenon or object; and final causes, the purpose of whatever object we are investigating. For example, let’s say we want to investigate the “causes” of the Brooklyn Bridge. Its material cause would be encompassed by a description of the physical materials that went into its construction. The formal cause is the fact that it is a bridge across a stretch of water, and not either a random assembly of pieces or another kind of orderly structure (such as a skyscraper). The efficient causes were the blueprints drawn by engineers and the labor of men and machines that actually assembled the physical materials and put them into place. The final cause of the Brooklyn Bridge was the necessity for people to walk and ride between two landmasses without getting wet.

Dembski maintains that Bacon and his followers did away with both formal and final causes (the so-called teleonomic causes, because they answer the question of why something is) in order to free science from philosophical speculation and ground it firmly into empirically verifiable statements. That may be so, but things certainly changed with the work of Charles Darwin (1859). Darwin was addressing a complex scientific question in an unprecedented fashion: he recognized that living organisms are clearly designed in order to survive and reproduce in the world they inhabit; yet, as a scientist, he worked within the framework of naturalistic explanations of such design. Darwin found the answer in his well-known theory of natural selection. Natural selection, combined with the basic process of mutation, makes design possible in nature without recourse to a supernatural explanation because selection is definitely nonrandom, and therefore has “creative” (albeit nonconscious) power. Creationists usually do not understand this point and think that selection can only eliminate the less fit; but Darwin’s powerful insight was that selection is also a cumulative process-analogous to a ratchet-which can build things over time, as long as the intermediate steps are also advantageous.

Darwin made it possible to put all four Aristotelian causes back into science. For example, if we were to ask what are the causes of a tiger’s teeth within a Darwinian framework, we would answer in the following manner. The material cause is provided by the biological materials that make up the teeth; the formal cause is the genetic and developmental machinery that distinguishes a tiger’s teeth from any other kind of biological structure; the efficient cause is natural selection promoting some genetic variants of the tiger’s ancestor over their competitors; and the final cause is provided by the fact that having teeth structured in a certain way makes it easier for a tiger to procure its prey and therefore to survive and reproduce-the only “goals” of every living being.

Therefore, design is very much a part of modern science, at least whenever there is a need to explain an apparently designed structure (such as a living organism). All four Aristotelian causes are fully reinstated within the realm of scientific investigation, and science is not maimed by the disregard of some of the causes acting in the world. What then is left of the argument of Dembski and of other proponents of ID? They, like William Paley (1831) well before them, make the mistake of confusing natural design and intelligent design by rejecting the possibility of the former and concluding that any design must by definition be intelligent.

One is left with the lingering feeling that Dembski is being disingenuous about ancient philosophy. It is quite clear, for example, that Aristotle himself never meant his teleonomic causes to imply intelligent design in nature (Cohen 2000). His mentor, Plato (in Timaeus), had already concluded that the designer of the universe could not be an omnipotent god, but at most what he called a Demiurge, a lesser god who evidently messes around with the universe with mixed results. Aristotle believed that the scope of god was even more limited, essentially to the role of prime mover of the universe, with no additional direct interaction with his creation (i.e., he was one of the first deists). In Physics, where he discusses the four causes, Aristotle treats nature itself as a craftsman, but clearly devoid of forethought and intelligence. A tiger develops into a tiger because it is in its nature to do so, and this nature is due to some physical essence given to it by its father (we would call it DNA) which starts the process out. Aristotle makes clear this rejection of god as a final cause (Cohen 2000) when he says that causes are not external to the organism (such as a designer would be) but internal to it (as modern developmental biology clearly shows). In other words, the final cause of a living being is not a plan, intention, or purpose, but simply intrinsic in the developmental changes of that organism. Which means that Aristotle identified final causes with formal causes as far as living organisms are concerned. He rejected chance and randomness (as do modern biologists) but did not invoke an intelligent designer in its place, contra Dembski. We had to wait until Darwin for a further advance on Aristotle’s conception of the final cause of living organisms and for modern molecular biology to achieve an understanding of their formal cause.

Irreducible Complexity

There are two additional arguments proposed by ID theorists to demonstrate intelligent design in the universe: the con-cept of “irreducible complexity” and the “complexity-specification” criterion. Irreducible complexity is a term introduced in this context by molecular biologist Michael Behe in his book Darwin’s Black Box (1996). The idea is that the difference between a natural phenomenon and an intelligent designer is that a designed object is planned in advance, with forethought. While an intelligent agent is not constrained by a step-by-step evolutionary process, an evolutionary process is the only way nature itself can proceed given that it has no planning capacity (this may be referred to as incremental complexity). Irreducible complexity then arises whenever all the parts of a structure have to be present and functional simultaneously for it to work, indicating-according to Behe-that the structure was designed and could not possibly have been gradually built by natural selection.

Behe’s example of an irreducibly complex object is a mousetrap. If you take away any of the minimal elements that make the trap work it will lose its function; on the other hand, there is no way to assemble a mousetrap gradually from a natural phenomenon, because it won't work until the last piece is assembled. Forethought, and therefore intelligent design, is necessary. Of course it is. After all, mousetraps as purchased in hardware stores are indeed human products; we know that they are intelligently designed. But what of biological structures? Behe claims that, while evolution can explain a lot of the visible diversity among living organisms, it is not enough when we come to the molecular level. The cell and several of its fundamental components and biochemical pathways are, according to him, irreducibly complex.

The problem with this statement is that it is contradicted by the available literature on comparative studies in microbiology and molecular biology, which Behe conveniently ignores (Miller 1996). For example, geneticists are continuously showing that biochemical pathways are partly redundant. Redundancy is a common feature of living organisms where different genes are involved in the same or in partially overlapping functions. While this may seem a waste, mathematical models show that evolution by natural selection has to produce molecular redundancy because when a new function is necessary it cannot be carried out by a gene that is already doing something else, without compromising the original function. On the other hand, if the gene gets duplicated (by mutation), one copy is freed from immediate constraints and can slowly diverge in structure from the original, eventually taking over new functions. This process leads to the formation of gene “families,” groups of genes clearly originated from a single ancestral DNA sequence, and that now are diversified and perform a variety of functions (e.g., the globins, which vary from proteins allowing muscle contraction to those involved in the exchange of oxygen and carbon dioxide in the blood). As a result of redundancy, mutations can knock down individual components of biochemical pathways without compromising the overall function-contrary to the expectations of irreducible complexity.

(Notice that creationists, never ones to loose a bit, have also tried to claim that redundancy is yet another evidence of intelligent design, because an engineer would produce backup systems to minimize catastrophic failures should the primary components stop functioning. While very clever, this argument once again ignores the biology: the majority of duplicated genes end up as pseudogenes, literally pieces of molecular junk that are eventually lost forever to any biological utility [Max 1986].)

To be sure, there are several cases in which biologists do not know enough about the fundamental constituents of the cell to be able to hypothesize or demonstrate their gradual evolution. But this is rather an argument from ignorance, not positive evidence of irreducible complexity. William Paley advanced exactly the same argument to claim that it is impossible to explain the appearance of the eye by natural means. Yet, today biologists know of several examples of intermediate forms of the eye, and there is evidence that this structure evolved several times independently during the history of life on Earth (Gehring and Ikeo 1999). The answer to the classical creationist question, “What good is half an eye?” is “Much better than no eye at all"!

However, Behe does have a point concerning irreducible complexity. It is true that some structures simply cannot be explained by slow and cumulative processes of natural selection. From his mousetrap to Paley’s watch to the Brooklyn Bridge, irreducible complexity is indeed associated with intelligent design. The problem for ID theory is that there is no evidence so far of irreducible complexity in living organisms.

The Complexity-Specification Criterion

William Dembski uses an approach similar to Behe to back up creationist claims, in that he also wants to demonstrate that intelligent design is necessary to explain the complexity of nature. His proposal, however, is both more general and more deeply flawed. In his book The Design Inference (Dembski 1998a) he claims that there are three essential types of phenomena in nature: “regular,” random, and designed (which he assumes to be intelligent). A regular phenomenon would be a simple repetition explainable by the fundamental laws of physics, for example the rotation of Earth around the Sun. Random phenomena are exemplified by the tossing of a coin. Design enters any time that two criteria are satisfied: complexity and specification (Dembski 1998b).

There are several problems with this neat scenario. First of all, leaving aside design for a moment, the remaining choices are not limited to regularity and randomness. Chaos and complexity theory have established the existence of self-organizing phenomena (Kauffman 1993; Shanks and Joplin 1999), situations in which order spontaneously appears as an emergent property of complex interactions among the parts of a system. And this class of phenomena, far from being only a figment of mathematical imagination as Behe maintains, are real. For example, certain meteorological phenomena such as tornados are neither regular nor random but are the result of self-organizing processes.

But let us go back to complexity-specification and take a closer look at these two fundamental criteria, allegedly capable of establishing intelligent agency in nature. Following one of Dembski’s examples, if SETI (Search for Extraterrestrial Intelligence) researchers received a very short signal that may be interpreted as encoding the first three prime numbers, they would probably not rush to publish their findings. This is because even though such signal could be construed as due to some kind of intelligence, it is so short that its occurrence can just as easily be explained by chance. Given the choice, a sensible scientist would follow Ockham’s razor and conclude that the signal does not constitute enough evidence for extraterrestrial intelligence. However, also according to Dembski, if the signal were long enough to encode all the prime numbers between 2 and 101, the SETI people would open the champagne and celebrate all night. Why? Because such signal would be both too complex to be explained by chance and would be specifiable, meaning that it is not just a random sequence of numbers, it is an intelligible message.

The specification criterion needs to be added because complexity by itself is a necessary but not sufficient condition for design (Roche 2001). To see this, imagine that the SETI staff receives a long but random sequence of signals. That sequence would be very complex, meaning that it would take a lot of information to actually archive or repeat the sequence (you have to know where all the 0s and 1s are), but it would not be specifiable because the sequence would be meaningless.

Dembski is absolutely correct that plenty of human activities, such as SETI, investigations into plagiarism, or encryption, depend on the ability to detect intelligent agency. Where he is wrong is in assuming only one kind of design. For him design equals intelligence and, even though he admitted that such an intelligence may be an advanced extraterrestrial civilization, his preference is for a god, possibly of the Christian variety.

The problem is that natural selection, a natural process, also fulfills the complexity-specification criterion, thereby demonstrating that it is possible to have unintelligent design in nature. Living organisms are indeed complex. They are also specifiable, meaning that they are not random assemblages of organic compounds, but are clearly formed in a way that enhances their chances of surviving and reproducing in a changing and complex environment. What, then, distinguishes organisms from the Brooklyn Bridge? Both meet Dembski’s complexity-specification criterion, but only the bridge is irreducibly complex. This has important implications for design.

In response to some of his critics, Dembski (2000) claimed that intelligent design does not mean optimal design. The criticism of suboptimal design has often been advanced by evolutionists who ask why God would do such a sloppy job with creation that even a mere human engineer can easily determine where the flaws are. For example, why is it that human beings have hemorrhoids, varicose veins, backaches, and foot aches? If you assume that we were “intelligent-ly” designed, the answer must be that the designer was rather incompetent-something that would hardly please a creationist. Instead, evolutionary theory has a single answer to all these questions: humans evolved bipedalism (walking with an erect posture) only very recently, and natural selection has not yet fully adapted our body to the new condition (Olshansky et al. 2001). Our closest primate relatives, chimps, gorillas, and the like, are better adapted to their way of life, and therefore are less “imperfect” than ourselves!

Dembski is of course correct in saying that intelligent design does not mean optimal design. As much as the Brooklyn Bridge is a marvel of engineering, it is not perfect, meaning that it had to be constructed within the constraints and limitations of the available materials and technology, and it still is subject to natural laws and decay. The bridge’s vulnerability to high winds and earthquakes, and its inadequacy to bear a volume of traffic for which it was not built can be seen as similar to the back pain caused by our recent evolutionary history. However, the imperfection of living organisms, already pointed out by Darwin, does do away with the idea that they were created by an omnipotent and omnibenevolent creator, who surely would not be limited by laws of physics that He Himself made up from scratch.

The Four Fundamental Types of Design and How to Recognize Them

Given these considerations, I would like to propose a system that includes both Behe’s and Dembski’s suggestions, while at the same time showing why they are both wrong in concluding that we have evidence for intelligent design in the universe. Figure 1 summarizes my proposal. Essentially, I think there are four possible kinds of design in nature which, together with Dembski’s categories of “regular” and random phenomena, and the addition of chaotic and self-organizing phenomena, truly exhaust all possibilities known to us. Science recognizes regular, random, and self-organizing phenomena, as well as the first two types of design described in figure 1. The other two types of design are possible in principle, but I contend that there is neither empirical evidence nor logical reason to believe that they actually occur.

The first kind of design is non-intelligent-natural, and it is exemplified by natural selection within Earth’s biosphere (and possibly elsewhere in the universe). The results of this design, such as all living organisms on Earth, are not irreducibly complex, meaning that they can be produced by incremental, continuous (though not necessarily gradual) changes over time. These objects can be clearly attributed to natural processes also because of two other reasons: they are never optimal (in an engineering sense) and they are clearly the result of historical processes. For example, they are full of junk, nonutilized or underutilized parts, and they resemble similar objects occurring simultaneously or previously in time (see, for example, the fossil record). Notice that some scientists and philosophers of science feel uncomfortable in considering this “design” because they equate the term with intelligence. But I do not see any reason to embrace such limitation. If something is shaped over time-by whatever means-such that it fulfills a certain function, then it is designed and the question is simply of how such design happened to materialize. The teeth of a tiger are clearly designed to efficiently cut into the flesh of its prey and therefore to promote survival and reproduction of tigers bearing such teeth.

The second type of design is intelligent-natural. These artifacts are usually irreducibly complex, such as a watch designed by a human. They are also not optimal, meaning that they clearly compromise between solutions to different problems (trade-offs) and they are subject to the constraints of physical laws, available materials, expertise of the designer, etc. Humans may not be the only ones to generate these objects, as the artifacts of any extraterrestrial civilization would fall into the same broad category.

The third kind of design, which is difficult, if not impossible, to distinguish from the second, is what I term intelligent-supernatural-sloppy. Objects created in this way are essentially indistinguishable from human or ET artifacts, except that they would be the result of what the Greeks called a Demiurge, a minor god with limited powers. Alternatively, they could be due to an evil omnipotent god that just amuses himself with suboptimal products. The reason intelligent-supernatural-sloppy design is not distinguishable from some instances (but by all means not all) of intelligent-natural design is Arthur C. Clarke’s famous third law: from the point of view of a technologically less advanced civilization, the technology of a very advanced civilization is essentially indistinguishable from magic (such as the monolith in his 2001: A Space Odyssey). I would be very interested if someone could suggest a way around Clarke’s law.

Finally, we have intelligent-supernatural-perfect design, which is the result of the activity of an omnipotent and omnibenevolent god. These artifacts would be both irreducibly complex and optimal. They would not be constrained by either trade-offs or physical laws (after all, God created the laws themselves). While this is the kind of god many Christian fundamentalists believe in (though some do away with the omnibenevolent part), it’s quite clear from the existence of human evil as well as of natural catastrophes and diseases, that such god does not exist. Dembski recognizes this difficulty and, as I pointed out above, admits that his intelligent design could even be due to a very advanced extraterrestrial civilization, and not to a supernatural entity at all (Dembski 2000).

Conclusions

In summary, it seems to me that the major arguments of Intelligent Design theorists are neither new nor compelling:

1. It is simply not true that science does not address all Aristotelian causes, whenever design needs to be explained;
2. While irreducible complexity is indeed a valid criterion to distinguish between intelligent and non-intelligent design, these are not the only two possibilities, and living organisms are not irreducibly complex (e.g., see Shanks and Joplin 1999);
3. The complexity-specification criterion is actually met by natural selection, and cannot therefore provide a way to distinguish intelligent from non-intelligent design;
4. If supernatural design exists at all (but where is the evidence or compelling logic?), this is certainly not of the kind that most religionists would likely subscribe to, and it is indistinguishable from the technology of a very advanced civilization.

Therefore, Behe’s, Dembski’s, and other creationists’ (e.g., Johnson 1997) claims that science should be opened to supernatural explanations and that these should be allowed in academic as well as public school curricula are unfounded and based on a misunderstanding of both design in nature and of what the neo-Darwinian theory of evolution (Mayr and Provine 1980) is all about.

Acknowledgments

I would like to thank Melissa Brenneman, Will Provine, and Niall Shanks for insightful comments on earlier versions of this article, as well as Michael Behe, William Dembski, Ken Miller, and Barry Palevitz for indulging in correspondence and discussions with me over these matters.

References

• Behe, M.J. 1996. Darwin’s Black Box: The Biochemical Challenge to Evolution. New York, N.Y.: Free Press.
• Cohen, S.M. 2000. The four causes. Accessed on 5/16/00 at faculty.washington.edu/smcohen.
• Darwin, C. [1859] 1910. The Origin of Species by Means of Natural Selection: Or, the Preservation of Favored Races in the Struggle for Life. New York, N.Y.: A.L. Burt.
• Dembski, W.A. 1998a. The Design Inference. Cambridge, UK: Cambridge University Press.
• ---. 1998b. Reinstating design within science. Rhetoric & Public Affairs 1:503-518.
• ---. 2000. Intelligent design is not optimal design. Accessed on 2/3/00 at www.meta-list.org.
• Edis, T. 2001. Darwin in mind: Intelligent Design meets artificial intelligence. Skeptical Inquirer 25(2): 35-39.
• Gehring, W.J., and K. Ikeo. 1999. Pax 6, mastering eye morphogenesis and eye evolution. Trends in Genetics 15:371-377.
• Johnson, P. 1997. Defeating Darwinism by Opening Minds. Downers Grove, Illinois: InterVarsity Press.
• Kauffman, S.A. 1993. The Origins of Order. New York, N.Y.: Oxford University Press.
• Max, E.E. 1986. Plagiarized errors and molecular genetics: Another argument in the evolution-creation controversy. Creation/Evolution 9:34-46.
• Mayr, E., and W.B. Provine. 1980. The Evolutionary Synthesis: Perspectives on the Unification of Biology. Cambridge, Mass.: Harvard University Press.
• Miller, K.R. 1996. The biochemical challenge to evolution. Accessed on 10/30/99 at biomed.brown.edu/faculty/M/Miller/Miller.html.
• Olshansky, S.J., A.C. Bruce, and R.N. Butler. 2001. If humans were built to last. Scientific American March, pp. 50-55.
• Paley, W. 1831. Natural Theology: Or, Evidences of the Existence and Attributes of the Deity, Collected from the Appearances of Nature. Boston, Mass: Gould, Kendall, and Lincoln, .
• Pigliucci, M. 2000. Chance, necessity, and the new holy war against science. A review of W.A. Dembski’s The Design Inference. BioScience 50(1): pp. 79-81. January.
• Roche, D. 2001. A bit confused: creationism and information theory. Skeptical Inquirer 25(2):40-42.
• Shanks, N., and K.H. Joplin. 1999. Redundant complexity: A critical analysis of intelligent design in biochemistry. Philosophy of Science 66:268-282.

At either end of the spectrum, to be sure, beholders have clarity. Evangelical and fundamentalist believers see a black-and-white world. They know the truth. All who do not see it their way are responsible for the world’s ills and therefore must be fought with every trick and tactic imaginable. Atheists are equally certain of the correctness of their nonbelief, and everyone else is deluded or at least a bit foolish. Most people are somewhere in between. Most people accommodate a complex system of multilevel, multidimensional, semi-compartmentalized beliefs and values.

That is true of many scientists and scientifically oriented people as well-although those involved in science probably do tend to have fewer adherents to blind belief and more who value and appreciate open-minded inquiry.

Many of the issues are private and personal. In the abstract, what you and I believe (or don't) are each our own business and no one else’s. Some of the issues are intellectual. Eminent theologians, great philosophers, Nobel laureate scientists have considered them in depth and shared their insights at length. But others have profound effects on the world-on society, on education, on public policy (and, unfortunately in some cultures where the conflicts have often gone to extremes, on life and limb).

The most troublesome example in the United States (which befuddles those elsewhere) is creationism. Creationists and their sympathizers would expunge from our schools even any mention of evolution - the central unifying idea of the biological sciences and one of the most beautiful and most powerfully explanatory concepts in the history of science. They do so in part because they mistakenly fear that evolution somehow undermines human values and dignity. Most of us may see that they are wrong about that, but at least we can see why they are so motivated.

Creationism and its latest spiffed-up manifestation, the “Intelligent Design” (ID) movement, have almost nothing to do with real science and real scientific controversies and everything to do with belief-laden personal and religious politics. But their promoters use scientific language and pretend they are presenting politicians, school board members, and the media valid alternative scientific views. All the while they denigrate every value that science holds dear. These values include unmitigated curiosity, a love of learning, a questioning attitude, an abhorrence of ideology and dogma, a commitment to open-minded inquiry, and an honest acknowledgment that all knowledge is tentative and open to revision (a subtle strength opponents portray and exploit as a serious weakness). Another essential value is a determination to let balanced assessments of facts and evidence guide policy judgments rather than using predetermined ideological views to decide which facts and evidence may be allowed to enter.

I was able to see creationist tactics at work first-hand earlier this year when leading ID proponent Phillip Johnson did a whirlwind speaking tour in New Mexico, where I live and work. Johnson is a UC Berkeley law professor, and as critics predicted before his appearances, he showed that he’s very clever at using rhetoric and tactics honed in the legal arena to argue a pretended case against evolution. He distorted, trivialized, and mischaracterized modern evolutionary science to a degree I found shameful. He presented a comic-book-like caricature of evolution that would be laughable if it were not so reprehensible. He bashed an entire broad field of vital science, and he was doing so not as an expert in biology or even in science but as a nonscientist author and ideologue.

But if you think this is clearly an instance where scientifically trained people are able to see through his techniques and realize the intellectual emptiness of the ID argument, you will be surprised. For I heard him at one of the nation’s foremost national scientific and engineering laboratories, a huge multiprogram government-funded laboratory that is advancing the frontiers of advanced technology daily, and the overwhelming sentiment of the audience of nearly 400 people there-virtually all scientists and engineers-was on his side. They ate it up. They laughed at his frequent jabs at “materialistic” science, as if their own engineering research was not based on the same science. It was astonishing in a way. In another sense I was not surprised at all.

A glimpse at some of the behind-the-scenes side issues surrounding his appearance shows just how complex and difficult the science and religion issue can be. His invitation to speak did not come from the national lab itself. The lab’s upper management was not even aware of his planned appearance until alerted a few weeks before his talk. He was invited by the lab’s Christians in the Workforce Networking Group, and most of the attendees were members of the group. The group had been officially sanctioned by the laboratory only as a result of legal action it pressed against the lab for such recognition. The group’s official status thus comes under the mandated equal employment opportunity/affirmative action (EEO/AA) part of the lab’s administrative operations, not anything to do with science. Furthermore, the group, despite its name, does not represent mainstream Christians at all, but a fundamentalist, evangelical wing. It requires a belief statement to join-ironic, given its EEO/AA home.

Once the lab’s management became aware of Johnson’s imminent appearance, it found itself in a diffi-cult position. Management didn't like having a person known for antiscience views speak at the lab, but it did not want to be accused of censorship and it did not want to create a controversy that would call attention to Johnson’s appearance. It decided to lay low and hope all would pass. Management did require the Christians in the Workforce Group to add a disclaimer to its official lab’s Web page. The disclaimer said the talk’s location in the lab’s main auditorium did not imply any laboratory or government agency “endorsement or approval of any of the concepts or ideas expressed.” (This disclaimer was not presented at the talk, however.) In the meantime, a quickly arranged talk by a pro-evolution scientist who some scientists had invited to counter the Johnson talk was canceled by management, on the grounds that that talk didn't have any official sanction-but mainly to avoid overt controversy. Johnson’s appearances at other, more public forums in the area got the public attention, and so the lay-low strategy, in a way, worked. But modern biology got roundly bashed at a national laboratory, without refutation.

This example is just a microcosm of how religiously motivated critics of evolution are making inroads in scientific and intellectual arenas. But it wouldn't have happened without a strongly sympathetic potential audience. The example shows that, in the United States at least, scientifically trained people themselves come from a broad spectrum of religious backgrounds, including fundamentalism, and quick generalizations are doomed to failure. If antievolution can be welcomed uncritically in a scientific setting, its acceptance is far easier among other parts of society. Leaders in politics (local to national), education, business, and media are no less diverse and no less vulnerable to distorted arguments against science, if the assertions fit preconceived viewpoints and well-formed mental templates.

The creationist cause continues to be pressed at all levels. In Kansas, where vigilant scientists and educators finally were able to overthrow a creationist takeover of the Kansas State Board of Education, word comes that creationist politicians and supporters are already gearing up to re-take control. At the national level, a comprehensive U.S. Senate education bill debated for six weeks had attached to it at the last minute a two-sentence amendment drafted by evolution opponents. The innocent-sounding amendment encourages teaching the “controversy” surrounding biological evolution. Its creationist origins are crystal clear: controversies surrounding no other areas of science are singled out. Amidst a flurry of other amendments, the Senate voted 91-8 in favor of the provision on the way to approving the entire education bill by the same margin. Again, a seemingly small inroad, but. . . .

Well, the creationist anti-evolution movement may be among the most pernicious manifestations of conflict between science and religion-or perhaps in this case between good science and bad religion-but related issues, controversies, and concerns are rampant. They always have been, and probably always will be. We're all human, and science and religion, despite their vast differences, are both very human enterprises.

This special expanded issue of the Skeptical Inquirer is devoted almost entirely to this turbulent interface between science and religion. It can be considered a continuation of our first special issue on the subject, “Science and Religion: Conflict or Conciliation?”, Vol. 23 No. 4, July/August 1999.

(These comments of mine are a continuation as well of my more detailed introduction to that issue; all the points I made there still pertain.) That issue provoked more positive reaction than any other in our history.

One reason I think it was so successful is that for the most part it combined a forthright defense of science’s highest values (in fact a whole bunch of such defenses) with a counseled respect for deeply held personal views. It forthrightly dealt with all conflicts, without personalizing issues in a way that offended sincere believers who also respect science. This is a difficult line to hew, but it can be done. At the same time, it presented a broad spectrum of views, all expressing legitimate scientific viewpoints, on issues of science and religion. Each author could argue points in whatever style and voice was desired, and that variety too seemed appreciated.

The same is true this time. And this time, as before, no consensus should be expected. Scientists and science-minded skeptics are located at many points along the spectrum of views. I hope the articles work as a prism to expand our perception of each of those viewpoints, bringing greater clarity and some greater appreciation of distinctions.

We hope you enjoy the articles. We invite you to share your own insights with us, and we promise to make room in future issues for at least selected samples of your reactions.

In order to explore some of the thinking processes involved in the current dialogue between science and religion, I have imagined the following fable. The characters in my fable are modern-day versions of Galileo, Newton, and Leibniz. Also included is a lesser known historical figure, theologian Richard Bentley, with whom Newton corresponded. Galileo is pictured as a modern-day experimental physicist, performing increasingly precise experiments with falling bodies at the Leaning Tower of Pisa. I imagine him rapidly communicating his results by e-mail to Newton in Cambridge, who is contemporaneously developing his laws of motion and gravity. Of course, Galileo preceded the other characters by two generations, so this interchange is obviously not historical. Furthermore, although both men were brilliant theorists and experimentalists, I am going to impose a modern division of labor and have Galileo be strictly an experimentalist and Newton a theorist. Galileo will have the best modern equipment at his disposal, and I will imagine each as if he thought like a scientist of today, not one of the sixteenth and seventeenth centuries.

Bentley is pictured discussing Galileo’s experimental results and their theological implications with Newton and Galileo over the Internet. I show Newton doing his best to explain the data by means of natural laws and, like typical modern theoretical physicists (that is, those who do not attempt to write popular books), not fretting too much about theology. While the historical Newton branched off into theology and alchemy, this was later in life. In my scenario he is still a typical (for today) young researcher, impatient with philosophizing and eager to get on with his work with minimum distraction.

Bentley seeks the God of the Gaps, looking for places where Newton’s theories seem to leave room for the Creator to impose his will. He exhibits the general misunderstanding and resulting distrust of scientific method that typifies the modern intellectual, who is intelligent but lacks scientific training and, worse, has little comprehension of scientific method. Galileo expresses religious skepticism more openly than he could in his day, but would have no trouble getting away with today. Finally, Leibniz joins the discussion near the end. He represents the new crop of science-theists who, unlike Bentley, know their science and mathematics but still think they see God’s hand in physics and cosmology.

In his initial, crude experiments, Galileo measures the times, t, that it takes cannonballs of various weights to drop from balconies in the tower at different heights h. He makes a graph of h vs. t and shows that the data fit a parabolic curve, h = kt² , with k a constant equal to 4.9 when h is measured in meters and t in seconds.

Gallileo, Newton, Bentley, and Leibniz

When Newton sees these results he e-mails Bentley and Galileo:

“Dear Friends: This is exactly what is predicted by my laws of motion and gravity. My second law of motion is F = ma, where F is the force on a body, m is its mass, and a is its acceleration. Putting it together with my law of gravity gives a = g, where g = 9.8 meters per second squared is the acceleration due to gravity, independent of the mass m. Using the methods of calculus, which I invented despite the claims of that upstart Leibniz, I then get h = kt² where k = g/2 = 4.9.”

Bentley finds Newton’s explanation difficult to under-stand: “Isaac, as usual I do not have a clue what you are talking about :). It all seems rather magical to me. Why should this 'calculus’ of yours, with all those strange symbols, have anything to do with reality?”

Newton responds, “Richard, I don't know why, but it seems to. I frame no hypotheses. I just calculate and compare my calculations with the data.”

In the meantime, Galileo continues his experiments with objects other than cannonballs and discovers something new. He drops a crumpled-up piece of paper, along with a rock. Releasing them at the same time from the same height, the paper hits the ground after the rock. A sheet of paper, and then a feather, take even longer.

When Bentley sees this result he excitedly types:

“See, Isaac, your theory is incomplete. God is acting to hold up the paper and the feather. This explains how birds and angels fly! God wills it.”

Galileo, who has been quiet so far except for supplying the data, butts in:

“I've never seen any angels, even with my telescope. But birds must fly by taking advantage of the upward force of the air, as de Vinci has suggested.”

Newton does not take long to respond: “In the original experiments, Galileo was dropping heavy objects-cannonballs. So I neglected the effect of air resistance, which I guessed would be small in that case. In general, however, the air is expected to exert an upward force that subtracts from the downward force of gravity, and this will be important for lighter objects. This resistive force depends on the velocity at which the body falls. I have modeled it as proportional to the square of the velocity and determined an air resistance coefficient from the data, which varies from object to object. Using some more calculus, I have obtained a fairly reasonable fit to Galileo’s data, as you can see by the attached graphs.”

Bentley is not too impressed: “That looks like a pretty ad hoc procedure to me. And so complicated! Only two people in the world can make such a calculation, Newton and Leibniz. Are we to rely on the authority of just the two of you? I prefer to rely on the authority of scriptures and the Church fathers. They provide a much simpler explanation that even the humblest peasant can understand, namely that God directs the motion of all things, from falling leafs to flying birds.”

Galileo is a bit annoyed: “I think I can manage this calculus too. After all, I am a professor of mathematics! But, more important, where in the God theory can you obtain the detailed, quantitative results Isaac has here? He can make all kind of predictions about falling bodies and projectiles. Even the Biblical prophets could not do that.”

“They were men of peace, not interested in bombs and cannonballs,” Bentley reverently but irrelevantly replies.

Things only get worse when Galileo reports another strange anomaly. His falling bodies do not hit the ground at a point directly below the release point, as marked precisely by a plumb bob, but slightly off to the east. He is careful to show that this is not an effect of winds.

“Aha,” Bentley cries, when the data appear on the Web. “Here is more evidence for God’s action. The Creator is blowing the objects off to the east.”

“Why would he do that?” Galileo questions.

“This is just one of those mysteries we were not meant to understand,” Bentley answers.

Newton scratches his head but soon realizes what is happening. “My previous calculations assumed that Earth is not accelerating. In fact, the rotation about its axis constitutes an acceleration. When I properly add this term to my equations, I get exactly what Galileo observes.”

“More ad hoc fixes and fudge factors,” Bentley retorts scathingly. “And look at those equations now. How complicated can they get? What purpose are you serving with all these esoteric symbols? It looks to me like you are starting a new cult, and you know what the Church thinks of cults!”

“Christianity was once a cult,” Galileo sourly answers.

Newton tries to cool things off. “Bentley, it is too bad you have not been able to follow my mathematics. (Damn these lousy schools.) If you could do the maths, you would see that my equations already contained the solutions to all the problems raised by Galileo’s increasingly more precise measurements. The F in F = ma represents the sum of the forces on a body. The term I added for air resistance in retrospect should have been included all along. Similarly, the a in F = ma must include the acceleration of Earth. Putting in the correct acceleration we again get what Galileo measures. What happens in the present case is that, because it is farther from the center of Earth, the body at its point of release has a greater eastward component of velocity than a point on the ground and so it drifts to the east relative to that point. And here is a falsifiable prediction! If Galileo does experiments with cannon balls shot straight up in the air, they will drift to the west.”

Back in Italy, Galileo is presented with a huge grant from Cosimo de Medici, from which he purchases lasers and a highly accurate atomic clock. Repeating his experiments, he finds that, even after corrections for air resistance and Earth’s rotation, the g in Newton’s equations is not a constant but depends on the height of the tower balcony from which objects are dropped.

Once again, Bentley goads Newton: “This surely proves that your theory is, at best, an approximation and so cannot be related in any important way to 'ultimate reality.' Each time our friend Galileo makes a better experiment, you have to modify your equations to make them agree with his data. What are you going to do now about this non-constant value of g?”

“Well, if you could follow the maths you would see that this, too, is in my equations. When I conceived the law of gravity I realized it applies to objects far from Earth, such as the Moon, as well as apples and leaves falling from trees. The Moon, in a sense, is falling toward Earth like an apple; but, because of its speed in orbit, it falls around Earth without ever hitting it. From estimates of the Moon’s distance and the time it takes to go around Earth, one month, I was able to infer that the force of gravity, and thus the acceleration of a falling body, will decrease as the square of its distance to the center of Earth. In fact, my law of gravity reads F = GmM/r² as the force between two bodies of masses m and M whose centers of gravity are separated by a distance r, where G is a constant determined from the data.

“The resulting acceleration on a body of mass m toward Earth is then g = GM/r² where M is the mass of Earth and r is the distance to the center. The variation with r is normally unmeasurable near Earth’s surface, since the difference between r and the radius of Earth R is small. So we are justified in neglecting it for most practical purposes. However, Galileo was able to detect the variation with his lasers and atomic clock.”

“If I can't read your equations, neither can the great majority of the human race,” Bentley responds. “How are you ever going to convince them?”

Newton sighs. “Okay, let me try to explain the significance of what I have done in words, which are unfortunately more imprecise than the maths. I have provided techniques that enable a sufficiently trained person to make quantitative calculations of precise measurements that agree with all the data. These equations also enable that person to make predictions about the motions of bodies that can be later tested by experiments. I hope Galileo and others will carry out these tests of my theories. My good friend Edmund Halley has just informed me that my equations predict that the recent comet will return again in seventy-five years. Unfortunately we will not be here to see if this prediction comes true. Even if some of these predictions fail, this could simply mean that I have once again made too many simplifying assumptions in my calculation, as I did when originally neglecting air friction or Earth’s rotation. The comet prediction should be an accurate one, however, since neither Halley nor I can think of any factors that may mess it up.

“Bentley, you have continually derided the fact that I did not anticipate some of Galileo’s measurements before they were made. But rather than taking this as a point against the validity of my theories, you should regard it as a point for!”

Bentley blinks. “Come again?”

“The fact that even I, the inventor of the theories, did not realize all their implications indicates, rather strongly I think, that they indeed have something to do with reality. In fact, you might say that I was not the inventor of the theories but rather their discoverer. They were out there in nature waiting for someone brilliant like me to come along to find them. Let me contrast my theories with yours, dear Bentley, that God has done it all. You claim your theory is simpler, and so more preferable, more likely to be correct than my complicated calculus equations.

“But is it simpler? I have been able to classify a wide range of phenomena, on Earth and in the heavens, with a few assumptions that are very simple in their own right. The complications you worry about are only in the manipulations, which admittedly require some inborn talent comparable to playing a musical instrument well.”

Galileo then jumps in with a thought: “Perhaps, someday, humans will possess machines that will do these calculations for them. Then all they will have to do is put in the initial positions and velocities, and predict the future motion of all bodies. If Lucretius is correct -- that everything is made up of atoms -- then everything will be predictable.”

Suddenly, Bentley breaks out into a broad grin and excitedly types: “Even if you are correct, and everything that happens in the universe can ultimately be predicted by some huge machine, the hand of the Creator was still involved. You have just written down some esoteric equations, but you have not told me where those equations come from. I think it is all pretty obvious. They came from God!”

“Why did they have to come from anything?” Galileo interjects.

“Everything comes from something.”

“And God, where did he come from?”

“Well, God is the exception. As Aristotle said, the first cause uncaused.”

“Why can't that exception be the universe itself?”

Bentley does not answer, since he has become troubled by another thought: “I don't think I like this idea after all. What happens to free will?”

“I will leave it to you theologians to figure that one out,” Galileo responds.

Newton has not said much for a while and now speaks up: “Actually, now that you have distracted me from my research and dragged me into a theological discussion, I must admit that my theory does not account for everything. Remember I said that my law of gravity does not give the value of G. I have to get that from the data. Also, recall that the Moon is like a falling object. My equations will tell you that the Moon’s orbit around Earth is elliptical, but they do not give the orientation of the axes of the ellipse.”

“Ah, better yet!” Bentley exclaims. “We are back exactly to the God of the Bible. He creates the universe with its matter and light. He commands this matter and light to obey certain natural laws, which you scientists are now beginning to discover. But the Creator sees to it that the laws do not preordain all that happens. Humans then have the free will to act, from which we get evil despite God’s innate goodness. All this freedom, however, can lead to things getting out of hand. So, God acts whenever necessary to keep the universe and mankind moving on track toward the ultimate realization of his divine plan.”

Just then an e-mail comes in from Leibniz in Germany:

“I just happened to get wind of this discussion while surfing the Web. I have looked at Newton’s equations on his Web page and can confirm that they fit Galileo’s data. In fact, I did invent calculus independently and used my own methods which I think are superior, especially in terms of notation.”

Newton: “Balderdash!”

“In any case,” Leibniz continues, “I have to go along with Bentley that God’s purpose is evident in all that is being uncovered here. Let’s take Newton’s constant G in his theory of gravity. He admits that his theory does not give its value, that it must be determined by experiment. I am sure that Bentley will agree that it must be set by God.”

Bentley responds, “Indubitably.”

“But I have more,” Leibniz types. “I think I can prove that God has set this value of G very precisely for the divine purpose of making human life possible. Newton’s equations, which I truly do admire despite their lamentable notation, have allowed me to calculate, with my own better methods, the effect that different values of G would have on the orbit of Earth. Earth might have been farther from the Sun and too cold for life, or closer to the Sun and too hot.”

Newton replies, “Yes, yes. This is just the r³/T² = a constant law discovered observationally by Kepler which I have already proven from my theory. Note that if G were different we could have the same orbital radius r as now with just a different orbital period T.”

“I agree,” says Leibniz. “But with all the values of r and G to chose from, how unlikely it is that a random selection would have given just the right values we need for our existence? Suppose we had a world in which a year was not 365 days. I shudder to think of what this would do to the seasons. I would wager that human life would again be impossible. As far as I can see, only the exact value of G, and the specific values of r and T we have, would allow for human life. God has obviously chosen these numbers carefully and created this as the best of all possible worlds.”

“Or, the worst,” Galileo replies. “It could all be just one, big accident.”

The American philosopher Charles Sanders Peirce somewhere remarked that unfortunately universes are not as plentiful as blackberries. One of the most astonishing of recent trends in science is that many top physicists and cosmologists now defend the wild notion that not only are universes as common as blackberries, but even more common. Indeed, there may be an infinity of them!

It all began seriously with an approach to quantum mechanics (QM) called “The Many Worlds Interpretation” (MWI). In this view, widely defended by such eminent physicists as Murray Gell-Mann, Stephen Hawking, and Steven Weinberg, at every instant when a quantum measurement is made that has more than one possible outcome, the number specified by what is called the Schrödinger equation, the universe splits into two or more universes, each corresponding to a possible future. Everything that can happen at each juncture happens. Time is no longer linear. It is a rapidly branching tree. Obviously the number of separate universes increases at a prodigious rate.

If all these countless billions of parallel universes are taken as no more than abstract mathematical entities-worlds that could have formed but didn't-then the only “real” world is the one we are in. In this interpretation of the MWI the theory becomes little more than a new and whimsical language for talking about QM. It has the same mathematical formalism, makes the same predictions. This is how Hawking and many others who favor the MWI interpret it. They prefer it because they believe it is a language that simplifies QM talk, and also sidesteps many of its paradoxes.

There is, however, a more bizarre way to interpret the MWI. Those holding what I call the realist view actually believe that the endlessly sprouting new universes are “out there,” in some sort of vast super-space-time, just as “real” as the universe we know! Of course at every instant a split occurs each of us becomes one or more close duplicates, each traveling a new universe. We have no awareness of this happening because the many universes are not causally connected. We simply travel along the endless branches of time’s monstrous tree in a series of universes, never aware that billions upon billions of our replicas are springing into existence somewhere out there. “When you come to a fork in the road,” Yogi Berra once said, “take it.”

It is true that the MWI, in this realist form, avoids some of the paradoxes of QM. The so-called “measurement problem,” for example, is no longer a problem because whenever a measurement occurs, there is no “collapse of the wave function” (or rotation of the state vector in a different terminology). All possible outcomes take place. Schrödinger’s notorious cat is never in a mixed state of alive and dead. It lives in one universe, dies in another. But what a fantastic price is paid for these seeming simplicities! It is hard to imagine a more radical violation of Occam’s razor, the law of parsimony which urges scientists to keep entities to a minimum.

The MWI was first put forth by Hugh Everett III in a Princeton doctoral thesis written for John Wheeler in 1956. It was soon taken up and elaborated by Bryce DeWitt. For several years John Wheeler defended his student’s theory, but finally decided it was “on the wrong track,” no more than a bizarre language for QM and one that carried “too much metaphysical baggage.” However, recent polls show that about half of all QM experts now favor the theory, though it is seldom clear whether they think the other worlds are physically real or just abstractions such as numbers and triangles. Apparently both Everett and DeWitt took the realist approach. Roger Penrose is among many famous physicists who find the MWI appalling. The late Irish physicist John S. Bell called the MWI “grotesque” and just plain “silly.” Most working physicists simply ignore the theory as nonsense.

In an article on “Quantum Mechanics and Reality” (in Physics Today, September 1970), DeWitt wrote with vast understatement about his first reaction to Everett’s thesis: “I still recall vividly the shock I experienced on first encountering the multiworld concept. The idea of 10¹⁰⁰⁺ slightly imperfect copies of oneself all constantly splitting into further copies, which ultimately become unrecognizable, is not easy to reconcile with common sense. This is schizophrenia with a vengeance!”

In the MWI, most of its defenders agree, there is no room for free will. The multiverse, the universe of all universes, develops strictly along determinist lines, always obeying the deterministically evolving Schrödinger equation. This equation is a monstrous wave function which never collapses unless it is observed and collapsed by an intelligence outside the multiverse, namely God.

In recent years David Deutsch, a quantum physicist at Oxford University, has become the top booster of the MWI in its realist form. He believes that quantum computers, using atoms or photons and operating in parallel with computers in nearby parallel worlds, can be trillions of times faster than today’s computers. He is convinced that many famous QM paradoxes, such as the double slit experiment and a similar one involving two half-silvered mirrors, are best explained by assuming an interaction with twin particles in a parallel world almost identical with our own. For example, in the double slit experiment, when both slits are open, our particle goes through one slit while its twin from the other world goes through the other slit to produce the interference pattern on the screen.

Deutsch calls our particle the “tangible” one, and the particle coming from the other world a “shadow” particle. Of course in the adjacent universe our particle is the shadow of their tangible particle. Because communication between universes is impossible, it is hard to imagine why a particle would bother to jump from one universe to another just to produce interference.

Deutsch believes that the results of calculating simultaneously in parallel worlds can somehow be brought back here to coalesce. Critics argue that QM paradoxes, as well as quantum computers, are just as easily explained by conventional theory or by such rivals as the pilot wave theory of David Bohm. In any case, Deutsch’s 1997 book The Fabric of Reality: The Science of Parallel Universes-and Its Implications is the most vigorous defense yet of a realistic MWI.

Deutsch is fully aware that the MWI forces him to accept the reality of endless copies of himself out there in the infinity of other worlds. “I may feel subjectively,” he writes (p. 53), “that I am distinguished among the copies as the 'tangible' one, because I can directly perceive myself and not the others, but I must come to terms with the fact that all the others feel the same about themselves. Many of those Davids are at this moment writing these very words. Some are putting it better. Others have gone for a cup of tea.” And he is puzzled by the fact that so few physicists are as enthralled as he about the MWI!

Theoretical and experimental work on quantum computers is now a complex, controversial, rapidly growing field with Deutsch as its pioneer and leading theoretician. You can keep up with this research by clicking on Oxford’s Centre for Quantum Computation’s Web site www.qubit.org.

The MWI should not be confused with a more recent concept of a multiverse proposed by Andrei Linde, a Russian physicist now at Stanford University, as well as by a few other cosmologists such as England’s Martin Rees. This multiverse is essentially a response to the anthropic argument that there must be a Creator because our universe has so many basic physical constants so finely tuned that, if any one deviated by a tiny fraction, stars and planets could not form-let alone life appear on a planet. The implication is that such fine tuning implies an intelligent tuner.

Linde’s multiverse goes like this. Every now and then, whatever that means, a quantum fluctuation precipitates a Big Bang. A universe with its own space-time springs into existence with randomly selected values for its constants. In most of these universes those values will not permit the formation of stars and life. They simply drift aimlessly down their rivers of time. However, in a very small set of universes the constants will be just right to allow creatures like you and me to evolve. We are here not because of any overhead intelligent planning but simply because we happen by chance to be one of the universes properly tuned to allow life to get started.

David Lewis

We come now to a third kind of multiverse, by far the wildest of the three. It has been set forth not by a scientist but by a peculiar philosopher, now at Princeton University, named David Lewis. In his best-known book, The Plurality of Worlds (Oxford, 1986), and other writings, Lewis seriously maintains that every logically possible universe-that is, one with no logical contradictions such as square circles-is somewhere out there. The notion of logical possible worlds, by the way, goes back to Leibniz’s Theodicy. He speculated that God considered all logically possible worlds, then created the one He deemed best for His purposes.

Both the MWI and Lewis’s possible worlds allow time travel into the past. You need never encounter the paradox of killing yourself, yet you are still alive, because as soon as you enter your past the universe splits into a new one in which you and your duplicate coexist.

Most of Lewis’s worlds do not contain any replicas of you, but if they do they can be as weird as you please. You can't, of course, simultaneously have five fingers on each hand and seven on each hand because that would be logically contradictory. But you could have a hundred fingers, and a dozen arms, or seven heads. Any world you can think of without contradiction is real. Can pigs fly? Certainly. There is nothing contradictory about pigs with wings. In an infinity of possible worlds there are lands of Oz, Greek gods on Mount Olympus, anything you can imagine. Every novel is a possible world. Somewhere millions of Ahabs are chasing whales. Somewhere millions of Huckleberry Finns are floating down rivers. Every kind of universe exists if it is logically consistent.

David Lewis’s mad multiverse was anticipated by hordes of science-fiction writers long before the MWI of QM came from Everett’s brain. More recent examples include Larry Nivens’s 1969 story “All the Myriad Ways” and Frederick Pohl’s 1986 novel The Coming of the Quantum Cats. Jorge Luis Borges played with the theme in his story ”The Garden of Forking Paths.” There is a quotation from this tale at the front of The Many Worlds Interpretation of Quantum Mechanics (1973), a standard reference by DeWitt and Neill Graham. For other examples of multiverses in science fiction and fantasy see the entry on “Parallel Worlds” in The Encyclopedia of Science Fiction (1995) by John Clute and Peter Nichols.

Fredric Brown, in What Mad Universe (1950), described Lewis’s multiverse this way:

There are, then, an infinite number of coexistent universes.

“They include this one and the one you came from. They are equally real, and equally true. But do you conceive what an infinity of universes means, Keith Winton?”

“Well-yes and no.”

“It means that, out of infinity, all conceivable universes exist.

“There is, for instance, a universe in which this exact scene is being repeated except that you-or the equivalent of you-are wearing brown shoes instead of black ones.

“There are an infinite number of permutations of that variation, such as one in which you have a slight scratch on your left forefinger and one in which you have purple horns and-”

“But are they all me?”

Mekky said, “No, none of them is you-any more than the Keith Winton in this universe is you. I should not have used that pronoun. They are separate individual entities. As the Keith Winton here is; in this particular variation, there is a wide physical difference-no resemblance, in fact.”

Keith said thoughtfully, “If there are infinite universes, then all possible combinations must exist. Then, somewhere, everything must be true.”

“And there are an infinite number of universes, of course, in which we don't exist at all-that is, no creatures similar to us exist at all. In which the human race doesn't exist at all. There are an infinite number of universes, for instance, in which flowers are the predominant form of life-or in which no form of life has ever developed or will develop.

“And infinite universes in which the states of existence are such that we would have no words or thoughts to describe them or to imagine them.”

I have here looked at only the three most important versions of a multiverse. There are others, less well known, such as Penn State’s Lee Smolin’s universes which breed and evolve in a manner similar to Darwinian theory. For a good look at all the multiverses now being proposed, see British philosopher John Leslie’s excellent book Universes (1989).

I find it hard to believe that so many academics take Lewis’s possible worlds seriously. As poet Armand T. Ringer has put it in a clerihew:

David Lewis
Is a philosopher who is
Crazy enough to insist
That all logically possible worlds actually exist.

Alex Oliver, reviewing Lewis’s Papers in Metaphysics and Epistemology, in The London Times Literary Supplement (January 7, 2000), closes by calling Lewis “the leading metaphysician at the start of this century, head and beard above his contemporaries.”

The stark truth is that there is not the slightest shred of reliable evidence that there is any universe other than the one we are in. No multiverse theory has so far provided a prediction that can be tested. In my layman’s opinion they are all frivolous fantasies. As far as we can tell, universes are not as plentiful as even two blackberries. Surely the conjecture that there is just one universe and its Creator is infinitely simpler and easier to believe than that there are countless billions upon billions of worlds, constantly increasing in number and created by nobody. I can only marvel at the low state to which today’s philosophy of science has fallen.