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Astrophysical Fine-tuning, Naturalism and the Contemporary

By Stacy Webb,2014-06-17 12:25
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Astrophysical Fine-tuning, Naturalism and the ContemporaryFine,and,the,fine

    Astrophysical Fine-tuning, Naturalism and the Contemporary Design Argument

    Mark A. Walker

    Trinity College, University of Toronto

    15 Devonshire Place

    Toronto M5S 1H8, Canada

    mwalker@nmsu.edu

    Milan M. Ćirković

    Astronomical Observatory Belgrade

    Volgina 7, 11160 Belgrade

    Serbia and Montenegro

    mcirkovic@aob.aob.bg.ac.yu

1. FINE-TUNING IN ASTROPHYSICS. ............................................................................................. 1

    2. TYPES OF FINE-TUNING ............................................................................................................... 3

    3. EVIDENCE FOR FINE-TUNING ............................................................................................... 8

    3.1 EVIDENCE FOR MATHEMATICAL FINE-TUNING ................................................................................ 8 3.2 EMPIRICAL EVIDENCE FOR ANTHROPIC FINE-TUNING ...................................................................... 9 4. EXPLAINING ASTROPHYSICAL FINE-TUNING ....................................................................... 14

    4.1 THE COINCIDENCE EXPLANATION................................................................................................. 14 4.2 THE DESIGNER EXPLANATION ...................................................................................................... 17 4.3 THE LESSER DESIGNER EXPLANATION ....................................................................................... 19 4.4 THE MULTIVERSE EXPLANATION .............................................................................................. 20 4.5 THE NO FINE-TUNING ................................................................................................................. 23 4.4 THE NO EXPLANATION RESPONSE. ............................................................................................ 23 7. CONCLUSION ............................................................................................................................... 24

    MCALLISTER’S REVISIONS ........................................................................................................... 29

    REFEREE’S REPORT ....................................................................................................................... 33

    GUIDELINES FOR ARTICLE MANUSCRIPTS ............................................................................... 43

    4.1 THE ―NO THEORY THEORY‖SCRAPS ............................................................................................. 46

Abstract. Evidence for instances of astrophysical “fine-tuning” (or “coincidences”) is thought by some to

    lend support to the design argument (i.e., the argument that our universe has been designed by some deity). We assess some of the relevant empirical and conceptual issues. We argue that astrophysical fine-tuning call for some explanation but this explanation need not appeal to the design argument. A clear and strict separation of the issue of anthropic fine-tuning on one side and any form of Eddingtonian numerology and teleology on the other, may help clarify arguably the most significant issue of philosophy of cosmology.

    Key words: anthropic principle, philosophy of cosmology, selection effects, design argument

1. Fine-tuning in Astrophysics.

    Suppose you were asked to be the architect of a new universea heady responsibility to be sure. The

    only stipulation is that your universe must have the same fundamental constants as our universethe

    coupling constants for gravity, electromagnetism, weak and nuclear force, as well as quantities such as c, G

    or ; and (possibly) a few cosmological parameters such as the total energy density Ω or the initial entropy-

    per-baryon S. However, you are allowed latitude in what values you assign to these fundamental constants.

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    One way to proceed would be to assign these values by consulting a random number table. Using this procedure may speed your task along, but the resulting universe is not likely to be very ―appealing‖. The result might be somewhat analogous to using a random number table to determine the relative amounts of the ingredients when baking a cake. If you choose to be a little more energetic there are at least a couple of ways in which you could ―improve‖ your universe: you could provide it with some mathematical orderliness, or perhaps your concern might be to make it hospitable for sentient life. The former idea we will refer to as the idea of ‗mathematical fine-tuning‘ and the latter ‗anthropic fine-tuning‘.

    Astrophysicists (and others) have applied both of these ideas to our universe; but not always in a manner that makes it clear what is at issue. That there is some distinction to be drawn between these two types of fine-tuning may seem obvious, but a recent article critical of the idea of astrophysical fine-tuning in a well-known journal (Klee 2002) demonstrates the need to underscore this distinction. Klee believes that he has shown that a ―strong skepticism‖ about astrophysical fine-tuning is warranted. However, he does distinguish

    between mathematical and anthropic fine-tuning. Consider, in this connection, Klee‘s understanding of Carr

    and Rees' classic paper (1979). According to Klee, the ―chief motivating factor‖ for Carr and Rees is ―curiosity and the search for mathematical order.‖ However, this is to profoundly misunderstand Carr and Rees‘ groundbreaking work. Their study is one that looks to the relation between cosmological parameters and the existence of observers, that is, to anthropic rather than mathematical fine-tuning. Klee's article is a prototype of an entire cottage industry of studies critical of the anthropic reasoning, but based upon confusing and/or conflating two different concepts of fine-tuning (among other examples one may mention Barrow and Tipler 1986; Maynard-Smith and Szathmáry 1996; Mosterin 2000, 2004; Manson 2000). Our aim here is to attempt to disentangle these (and related) ideas as well as assess their applicability to our universe. In the next section we explore further the ideas of different types of fine-tuning. In section 3 we examine the evidence for fine-tuning in our universe. We argue that while there is little empirical evidence for mathematical fine-tuning of the universe, there is good (preliminary) evidence that our universe is anthropically fine-tuned. In section 4 we consider the question of how to explain fine-tuning in our universe. We argue further that there is a promising naturalistic explanation for the anthropic fine-tuning of our

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    universe that invokes the idea of a multiverse, and at present this explanation shows more potential than the alternatives, specifically; that it is merely fortuitous that our universe is anthropically fine-tuned, and some

    1version of the Design argument that appeals to the intentions of an architect of our universe.

    2. Types of Fine-Tuning

    One of our aims, then, is to show that the notion of ‗astrophysical fine-tuning‘ is often understood in a

    way that invites further clarification. One ambiguity turns on the observational and explanatory tasks associated with the investigation of fine-tuning. To illustrate this difference, imagine two astronomers who work side by side for years charting distant galaxies. A certain amount of consensus emerges after their hard labour: they agree that the universe exhibits appears to be designed. However, they disagree on the explanation why the universe appears to be designed. One thinks it is a matter of ―mere coincidence‖ that the universe appears to be designed. The second believes that the appropriate explanation lies in fact that there is a Designer of our universe. What we should say here is that the astronomers agree that the universe appears to be fine-tuned, but disagree on the explanation. Thus, we shall understand the idea of ‗fine-tuning‘

    as making no commitment to any particular explanation or theory about the nature of the astrophysical fine-tuning. So, to the extent that we can distinguish the activities of observing and theorizing, a commitment to fine-tuning is to make an observational claim, e.g., the universe (or some part of the universe) appears to be designed; whereas, to invoke a particular explanation for astrophysical fine-tuning is move more in the realm

    thof theory. This distinction is not without parallel: biologists at the end of the 19 century often agreed that

    organisms appear ―fine-tuned‖—e.g., that various biological systems of organisms appear to exhibit a great degree of designbut disagreed on the explanation for this observation. Some championed the new

    Darwinian naturalistic explanation for these observations; others defend the traditional view that these observations are best explained in terms of the work of a Designer. Now it must be admitted that our use of ‗fine-tuning‘ here does not always agree with its use in the literature, since some authors tend to lump what

     1 Terminological points: We refer to the ‗Design argument‘ with a capital to underscore the fact it invokes the intentions of an agent to distinguish it from possible confusion with the sorts of design that might be the product of some non-intentional process such as Darwinian natural selection. Furthermore, in this paper we use ‗naturalism‘ in the ontological sense that our universe has no designer; we do not use it in its methodological sense in which ‗naturalism‘

    might mean the adoption of the scientific method.

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    we are terming the ‗observational‘ and ‗theoretical‘ tasks together; however, at least for our purposes here it will be best to keep this activities distinct.

    As intimated above, a further ambiguity can be found amongst various different types of astrophysical fine-tuning, and thus, we want to urge the view that ‗astrophysical fine-tuning‘ ought to be seen as a ―genus‖

    which includes various species, among them mathematical and anthropic fine-tuning. Let us consider first the case of mathematical fine-tuning. The idea that the universe is characterized by mathematical orderliness as a design constraint is an ancient one: it is a doctrine associated with Pythagoras and his followers and it found its most famous expression in the Ancient world in Plato‘s Timaeus. Hermann Weyl (1919) might be thought

    of as the modern progenitor of the idea of mathematical fine-tuning. Weyl noticed a convergence on the

    4040number 10 from two quite different sources. According to Weyl, one arrives at 10 when relating

    electromagnetism and gravity. Specifically by taking the ratio of strength of an electron‘s electromagnetic

    40 force and the strength of gravitational force as a function of its mass, one arrives at the pure number of 10

    40 (the units of measure cancel). The same large number 10 is also derived when the radius of the observable

    universe is expressed in fundamental ―atomic units‖ of Bohr's radius. Building on the work of Weyl, Arthur

    40 Eddington (1923) began to see cosmic coincidences converging on (or near) three classes: the number 1, 10

    40 80and those that are a power of 10(like its square, 10, etc.). Certainly if Eddington is right about the

    convergence of these three classes of numbers, then our universe exhibits more mathematical orderliness than the ―random universes‖ where the constants are assigned according to a random number table. There is

    an obvious question here when we reflect on the idea that mathematical fine-tuning appeals ultimately to a ―mathematical aesthetic‖ criterion for universe creation: the idea of mathematical orderliness. Exactly what

    is ‗mathematical orderliness‘? We shall work with the intuitive idea that some universes might exhibit more mathematical elegance than others, as well as suggesting a few examples of this idea, while putting aside the seemingly difficult problem of a detailed analysis of exactly what this notion amounts to. (We conjecture that the problem is difficult, since it looks to be on par with other well-known problems in the philosophy of science such as explicating the notion of ‗simplicity‘. Thus, it is often suggested that, other things equal, we

    ought to prefer the theory that is simpler. However, philosophers of science have had a difficult time spelling

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    out exactly what simplicity amounts to, similarly, articulating the idea of mathematical fine-tuning may present similar difficulties).

    Weyl and Eddington tended to look at the very large and small features of our universe in their attempts to show that the universe is mathematically fine-tuned. However, it is worth noting that ―medium sized‖

    astrophysical objects too might exhibit mathematical fine-tuning. Imagine the Prime Number Universe (PNU). The PNU is where solar systems are based on prime numbers such that the number of planets in a solar system is always a prime number. In addition, every planet has a prime number of moons arranged such that planets with larger orbits have a larger prime number of moons. To get a fix on this, imagine what one would have to do to make our solar system into a member of the PNU: We might have to push into the sun or somehow else destroy the last two planets so that we have a prime number of seven in our solar system. Furthermore, we might add and subtract a few moons to yield the following pattern: Mercury would have two moons, Venus three, Earth five, Mars seven, Jupiter eleven, Saturn thirteen, Uranus seventeen. If modern astronomy had discovered that our solar system had this exact number of planets and moons then we would have been in an excellent position to say that the solar system is mathematically fine-tuned. If we think about a future when we our able to observe in more detail other solar systems, we might imagine evidence mounting that the universe as a whole is as described by the PNU: every other planetary system we examine has this same prime number configuration corroborating the PNU conjecture.

     Turning now to the idea of idea of anthropic fine-tuning we would do well to remind ourselves that this

    2notion is related to the concept of an ‗anthropic principle‘; a term which comes from Carter (1974) and

    refers to the idea that the values of fundamental constants of our universe are (purportedly) highly constrained by the contingent fact that human observers exist: what might otherwise seem to be possible values for the fundamental constants can be ruled out because they are inconsistent with (say) the existence of stars that are stable for billions of years, or with the existence of galaxies or supernovas. The ‗anthropic thinking‘ here is that both stable stars and supernovas are necessary for the evolution of intelligent life as we

    know it: the former as a home and energy source for life to evolve, the latter to produce the heavier elements

     2 On occasion we will use the singular ‗anthropic principle‘ although we acknowledge that this glosses over the fact that there are a number of different anthropic principles. See Chapter 3 of Bostrom (2002) for some discussion.

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    3in the periodic table necessary for many life processes. If Carter and others are right, the chance that a

    ―random universe‖ would be hospitable for humans is astronomically (as it were) small—almost all ―random

    universes‖ would be inhospitable to human life. The commitment to anthropic fine-tuning then is that our

    universe appears to be designed to be hospitable for human life. As is the case with mathematical fine-tuning, the commitment to anthropic fine-tuning is taken to be distinct from the explanatory question of how we should explain this observation. That is, should it be explained in terms of a Designer, or is there some naturalistic explanation for this?

    Before looking at the evidence for astrophysical fine-tuning, we should ask: Are these two types of fine-tuning jointly exhaustive? As far as serious astrophysical research goes, the answer seems to be yes. The literature may sometimes run these two types of fine-tuning together but, to the best of our knowledge, all serious research can be lumped under one of these two types of fine-tuning. Clearly, there are other logically possible types of fine-tuning. In the past it was thought that the universe was organized along aesthetic lines: the stars in the sky were said to represent various objects, e.g., ―Orion‘s Belt‖ and the ―Big Dipper‖ are configurations of stars that are said to represent familiar human objects. To the extent that one took seriously the idea that the stars are pictures of such things then one might say that the universe is ‗aesthetically fine-

    tuned‘. Imagine if the stars in the night sky formed a perfect outline of the young Elvis we would have good reason to say that the universe was aesthetically fine-tuned. In fact, there are a number of ways that a universe in theory could be fine-tuned. Imagine we discover that all the visible galaxies form an intricate pattern that looks exactly like a person slipping on a banana peel. Here we might think that the universe is humorously fine-tuned. (Well, to the extent that one finds ―Jerry Lewis‖ style humour humorous). The possibilities here are perhaps endless: in theory we could discover that the universe appeared to be designed to maximize the production of super novas, earth-sized planets, a certain element on the period table, animal flesh, etc. While it would be wrong to dismiss any of these exotic possibilities a priori, nevertheless the only

     3 It may be possible for other forms of intelligent life to develop under radically different conditionse.g., science-

    fiction is replete with intelligent beings of ―pure energy‖. Anthropic thinking is concerned with the conditions necessary

    for human life (as we know it) to develop.

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    two serious contenders in the field (at the moment) are mathematical fine-tuning and anthropic fine-tuning; so we shall confine our attention to them.

    Are these two types of fine-tuning mutually exclusive or mutually entailing? At least in the weak sense of what is logically possible, a negative verdict seems indicated, that is, it seems that the two concepts are logically independent. It seems that there is no a priori reason to suppose that there is or there is not overlap

    between the set of universes that exhibit mathematical fine-tuning and the set of universes that exhibit anthropic fine-tuning. In other words, there is nothing about the concept of mathematical fine-tuning that entails that all or any of the set of mathematically fine-tuned universes might be hospitable to human life; nor does the concept of anthropic fine-tuning entail the concept of mathematical fine-tuning. It seems perfectly conceivable that there might be universes that exhibit a high degree of mathematical fine-tuning without being hospitable to human life. For instance, we could have a world in which the fundamental physical and mathematical constants exactly satisfy a numerologically appealing relationship:

    149162536,!??echGThe Beautiful Theorem:

    But there is no reason to suppose that a universe that conforms to the Beautiful Theorem would support human life. So we can easily imagine a universe that exhibits all sorts of Eddington numerology, but which is inhospitable to life (imagine radiation levels too high to allow life to develop). On the other hand, we can imagine a universe that is delicately balanced in its fundamental constituents for human life, but does not exhibit the mathematical orderliness of a mathematically fine-tuned universe. On the other hand, there is no reason to suppose that the sets must be mutually exclusive: it may well be that many (universes that are hospitable to human life exhibit mathematical orderliness. So, a commitment to one form of fine-tuning does not, a priori imply or exclude a commitment to the other.

    But while the two concepts of fine-tuning are logically independent it may well be that the two concepts are nomologically related. The idea here is that while as a matter of logic the two notions are independent, they are related in terms of some physical laws, just as it is logically possible that

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    the reader of this paper is not attracted to its authors, but as a nomological necessity there is an attraction: a gravitational attraction. Similarly, we cannot rule out a priori the possibility that there are nomological relations between anthropic fine-tuning and mathematical fine-tuning. One possibility is advances in physics, for example, the currently-sought ―Theory of Everything‖, might

    reveal that mathematical fine-tuning and anthropic fine tuning are related in some law-like fashion. (We will discuss this possibility below).

    3. Evidence for Fine-Tuning

    In this section we argue that there is little empirical evidence that our universe exhibits mathematical fine-tuning, and argue that there is some preliminary evidence that the universe is anthropically fine-tuned. However, one of the points we hope to underscore is that making the case for anthropic fine-tuning is often more difficult than both its supporters and detractors seem to believe.

    3.1 Evidence for Mathematical Fine-tuning

    One way to see the lack of empirical data for the existence of mathematical fine-tuning is by an appreciation of its historical development. As indicated above, early speculation of the idea of astrophysical fine-tuning, from Pythagoras to Dirac (1938), focused on the existence of mathematical fine-tuning. Modern speculation on fine-tuning begins in the 1960‘s when there was a transition to an interest in anthropic fine-

    tuning with the writings of Carter, Carr and Rees, et al. Failure to appreciate the distinction between mathematical and anthropic fine-tuning encourages the error of seeing the history of thinking about fine-tuning as a seamless continuity. Once this distinction is appreciated, it is clear that thinking about fine-tuning has two distinct phases. (Although as we have noted above, some of the modern authors run these two types of fine-tuning together so the two distinct phases here are not always easy to see). Historically, the decisive point here is perhaps Dicke (1961) who demolished Dirac's large-number hypothesis. Dirac‘s hypothesis was,

    in turn, based upon the numerological speculations originating with Weyl and, as noted, widely promoted by Eddington. Dicke‘s argument is pivotal here because he employed a version of anthropic fine-tuning in the

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argument against Dirac‘s case for mathematical fine-tuning. [Milan, it might help to add a sentence or two by

    way of explanation as to what Dicke showed].

    It is worth noting that the conflation of these two types of fine-tuning is not limited to merely the detractors of the idea of astrophysical fine-tuning, nor is it correct to say that all discussion of mathematical fine-tuning has disappeared in modern (that is, post 1960‘s) discussion of fine-tuning. For instance, as

    mentioned briefly above, the monograph of Barrow and Tipler (1986)what Klee aptly describes as the

    ―Bible‖ of anthropic reasoning—is not entirely innocent of this confusion. What this suggests is that all those involved in this debate should be on guard against conflating the two types of fine-tuning. This little history lesson goes some way to explaining why mathematical fine-tuning has fallen out of favour. To this we should add that contemporary physical evidence provides little support for their hypothesis: we now know that the numerical regularities in, for instance, the value of fine-structure constant are very approximate and cannot be traced to a solution of a simple quadratic equation, as Eddington hoped. The number of particles in the universe is determined by complicated interplay between cosmological parameters (density Ω and cosmological constant Λ) and the Big Bang physics, which cannot be formulated in a simple arithmetical manner, etc. The project of unification of forces is, if anything, livelier than in Eddington‘s day, but in its modern clothes of, say, string theory, it is based upon arcane mathematical physics in which any traces of Eddington numerology have long vanished.

    To say this is of course not to deny the possibility that string theory or some other new physical theory might not qualify as a case of mathematical fine-tuning. Rather, it is to say that nothing on the horizon suggests that string theory or its competitors are mathematically fine-tuned.

    3.2 Empirical Evidence for Anthropic Fine-tuning

    It is our contention that, unlike purported cases of mathematical fine-tuning, the empirical case for anthropic fine-tuning is still very much alive and well. As noted, however, often both supporters and detractors make grandiloquent statements of the type ―phenomenon X is/isn‘t a manifest example of fine-

    tuning‖, while the details of serious astrophysical observational and theoretical effort are completely lost. We

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