Philosophy The Anthropic Principle
by
Alasdair Richmond
  • LAST REVIEWED: 07 October 2016
  • LAST MODIFIED: 26 August 2011
  • DOI: 10.1093/obo/9780195396577-0135

Introduction

The enduringly controversial “anthropic principle” was baptized by Brandon Carter in 1974. Seeking a balance between excessive anthropocentrism and excessive insistence on human typicality, Carter sought to summarize the complex interrelations between our existence as observers and the physical conditions we observe. All anthropic arguments note that conditions needed to produce context-sensitive observers set restrictions on the conditions such observers will probably observe. As Carter stresses, anthropic reasoning applies to observers tout court and not exclusively to human beings. (If you are a silicon-based observer, expect to live in conditions conducive to silicon-based life.) Likewise, anthropic reasoning need not carry teleological or design overtones. The most widely accepted anthropic principle is the weak anthropic principle (WAP): “What we can expect to observe must be restricted by the conditions necessary for our presence as observers” (Carter 1974, p. 291, cited under General Overviews). Thus, observers who require a delicate range of conditions will almost certainly be found only where those conditions are met. Context-sensitive observers will likely find themselves observing areas of space-time, which may well be atypical of the universe at large. Hence, WAP suggests we should beware of extrapolating the conditions we observe in our neighborhood to the universe as a whole. Thus, some claim anthropic reasoning offsets the Copernican “principle of mediocrity,” which counsels us to view ourselves as being as typical as possible. However, any tension between anthropic and Copernican thinking may be more apparent than real (see, e.g., Bostrom 2002, cited under General Overviews, or Roush 2003, cited under Ancestors of Anthropic Reasoning). The strong anthropic principle (SAP) generalizes WAP and says the presence of context-sensitive observers suggests the universe must be amenable to the evolution of such observers: “The Universe must have those properties which allow life to develop within it at some stage in its history” (Barrow and Tipler 1986, p. 21, cited under General Overviews). Further extensions of anthropic reasoning include the participatory anthropic principle (PAP) and the final anthropic principle (FAP). PAP generally specifies that observers in some sense determine or create the physical properties they observe, whereas FAP states that life, once created, will (or must) endure for all future time. This article offers brief guidance on overviews and anthologies, anthropic design arguments, testing anthropic arguments, and the notorious anthropic-related doomsday and simulation arguments. The primary focus is on philosophical anthropic works. Hence, little attention is paid to teleology in physics or biology, still less to quantum measurement problems or natural selection. Some less well-known pieces have been chosen partly in hopes they become better known.

General Overviews

The classic presentation of anthropic arguments is the comprehensive Barrow and Tipler 1986, which surveys a host of scientific phenomena amenable to anthropic explanation, outlines the philosophical ancestors of anthropic reasoning, and develops a highly controversial series of arguments designed to establish that human life is destined to play a unique role in the future evolution and maintenance of the universe. However, in many respects Barrow and Tipler 1986 offers a somewhat idiosyncratic view of anthropic thinking in that the authors offer several arguments designed to suggest that human beings in particular (not merely observers in general) may play a significant role in the sustenance and future of the universe. Such anthropocentric applications of anthropic thinking are not in line with the initial formulation in Carter 1974 or with many others. Likewise, Barrow and Tipler 1986 often uses “anthropic” as a synonym for “teleological,” admittedly a usage that friends and foes of anthropic thinking have often been happy to follow but that is nonetheless misleading. Bostrom 2002 is a useful source of correctives and alternative viewpoints to those expressed in Barrow and Tipler 1986. In particular, Bostrom 2002 argues that the more teleologically inspired versions of anthropic reasoning (especially the final anthropic principle [FAP]) advanced in Barrow and Tipler 1986 are actually antithetical to the original conception of anthropic reasoning in Carter 1974. Barrow 2001 relates anthropic ideas principally to three key issues: the likelihood that humans are just one of many intelligent life-forms in the universe, the explanatory merits (or otherwise) of many-worlds cosmologies, and the strengths of teleological inferences in the physical sciences. Barrow 2001 can usefully be read as updating and supplementing the very well-focused treatment of the “many-worlds” issues in Leslie 1986. Leslie 1989 considers the competing merits of many-worlds hypotheses at length, primarily defending the thesis that cosmic fine-tuning obliges a choice between either many-worlds or design. Smith 1994 challenges these claims in detail. Tipler 1988 is an essential, if idiosyncratic, compilation of important anthropic arguments and applications.

  • Barrow, John D. “Cosmology, Life, and the Anthropic Principle.” Annals of the New York Academy of Sciences 950 (2001): 139–153.

    DOI: 10.1111/j.1749-6632.2001.tb02133.xSave Citation »Export Citation »E-mail Citation »

    Interesting treatment of anthropic considerations concerning the age of the universe and the presence of observers. Considers what anthropic reasoning suggests about the possibility of extraterrestrial observers and other universes and discusses the competing merits of teleological and nonteleological explanations of fine-tuning.

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    • Barrow, John D., and Frank J. Tipler. The Anthropic Cosmological Principle. Oxford: Oxford University Press, 1986.

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      The widest-ranging single volume on anthropic phenomena yet produced. Discusses a very wide range of physical phenomena that may be amenable to anthropic explanation. Major source especially for participatory anthropic principle (PAP) and FAP.

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      • Bostrom, Nick. Anthropic Bias: Observation Selection Effects in Science and Philosophy. London: Routledge, 2002.

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        Far and away the philosophically best-informed treatment of anthropic issues in the literature. Among other noteworthy features, chapter 3 develops a very clear and insightful taxonomy of forms of anthropic reasoning and subjects some of the more speculative forms of anthropic reasoning to incisive criticism. Essential reading in this field. Now available free in its entirety online.

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        • Carter, Brandon. “Large Number Coincidences and the Anthropic Principle in Cosmology.” In Confrontation of Cosmological Theories with Observational Data. Edited by M. S. Longair, 291–298. Dordrecht, The Netherlands: Reidel, 1974.

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          The paper that essentially coined the term “anthropic principle.” Beginning with the large-number coincidences observed in force ratios and so on, Carter argues for the pervasive influence of observer-selection effects in many disparate areas of science. Reprinted in Leslie 1999 (cited under Anthologies).

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          • Leslie, John. “Anthropic Explanations in Cosmology.” PSA: Proceedings of the Biennial Meeting of the Philosophy of Science Association 1 (1986): 87–95.

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            Useful overview of the need for, and differing implications of, observer-selection explanations. Develops Leslie’s objections to the Hacking 1987 (cited under The Inverse Gambler’s Fallacy) “inverse gambler’s fallacy” (as of 1986 circulated only in draft manuscript form). Available online for purchase or by subscription.

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            • Leslie, John. Universes. London, Routledge, 1989.

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              Wide-ranging discussion of worlds making, which pursues anthropically relevant topics into more theological territory than many treatments. An excellent discussion in its own right, this volume’s main interest lies in arguing first that cosmic fine-tuning invites explanation, and second that viable explanations are restricted to versions of intelligent design or multiverse hypotheses. Also usefully points out that design and many-worlds hypotheses, although often presented as antithetical, can be upheld together.

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              • Smith, Quentin. “Anthropic Explanations in Cosmology.” Australasian Journal of Philosophy 72.3 (1994): 371–382.

                DOI: 10.1080/00048409412346161Save Citation »Export Citation »E-mail Citation »

                Besides offering a clearly argued and scientifically literate critical overview of anthropic explanations generally, develops a case (contra Leslie 1989 and elsewhere) to the effect that observed cosmological coincidences do not in fact invite the postulation of many worlds. Available online for purchase or by subscription.

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                • Tipler, Frank J. “The Anthropic Principle: A Primer for Philosophers.” PSA: Proceedings of the Biennial Meeting of the Philosophy of Science Association 2 (1988): 27–48.

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                  Useful but somewhat anthropocentric sketch of the various kinds of anthropic principles, offering definitions that explicitly restrict the principle to human or carbon-based life. Available online for purchase or by subscription.

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                  Bibliographies and Other Reference Resources

                  The classic online guide to anthropic resources is Bostrom 2010. However, Plantinga 2008 and Ratzsch 2010 both offer useful references and detailed arguments that situate anthropic reasoning more closely to religious, teleological, and design arguments.

                  Anthologies

                  Inevitably, anthropic arguments surface in the context of other debates in physics and especially cosmology. Articles from several volumes cited here also appear under different headings, but in each case, full bibliographic references are given. Biswas, et al. 1989 offers a refreshing range of scientific and sometimes mystically oriented views, while Bertola and Curi 1993 offers a selection of (sometimes very technical) scientific research on anthropic themes. Perhaps the most useful volume under this particular heading, Leslie 1999 is a key collection, helpfully placing the views of scientists and philosophers in perspective around a diverse range of anthropic themes. Longair 1974 is primarily devoted to the testing conditions for hypotheses in cosmology but is notable here for containing Brandon Carter’s inaugural use of the term “anthropic principle” (see Carter 1974, cited under General Overviews). More design oriented than the other anthologies mentioned herein, Manson 2003 usefully complements other collections of anthropic writings and is an essential guide to the modern scientific debate about design.

                  • Bertola, F., and Umberto Curi, eds. The Anthropic Principle: Proceedings of the Second Venice Conference on Cosmology and Philosophy. Cambridge, UK: Cambridge University Press, 1993.

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                    Wide-ranging collection of primarily scientific but often philosophically informed writings on anthropic topics.

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                    • Biswas, S., D. Mallik, and C. Vishveshwara, eds. Cosmic Perspectives: Essays Dedicated to the Memory of M. K. V. Bappu. Cambridge, UK: Cambridge University Press, 1989.

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                      Interesting collection of papers on cosmological and physical topics but often with a philosophical flavor. For our purposes, most notable for containing Brandon Carter’s thoughts on anthropic reasoning as a plausible complement of, and extension to, neo-Darwinian evolutionary thinking (see Carter 1989, cited under Anthropic Reasoning, Quantum Theory, and Evolution).

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                      • Leslie, John, ed. Modern Cosmology and Philosophy. Amherst, NY: Prometheus, 1999.

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                        Revised version of John Leslie, ed., Physical Cosmology and Philosophy (New York: Collier Macmillan, 1990). Extensive, well-chosen collection of articles on cosmological and physical topics, almost all of which impinge on anthropic issues. Notable for the range of views it contains on the value of anthropic reasoning. Reprints Carter 1974 (cited under General Overviews) and includes useful articles from Paul Davies and Stephen Jay Gould, among others.

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                        • Longair, M. S., ed. Confrontation of Cosmological Theories with Observational Data. Dordrecht, The Netherlands: Reidel, 1974.

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                          Largely devoted to papers on the testing conditions of various cosmological hypotheses but contains Brandon Carter’s important paper in which the term “anthropic principle” was first coined (see Carter 1974, cited under General Overviews).

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                          • Manson, Neil A., ed. God and Design: The Teleological Argument and Modern Science. London: Routledge, 2003.

                            DOI: 10.4324/9780203398265Save Citation »Export Citation »E-mail Citation »

                            Well-nigh indispensable anthology of articles from a range of expert perspectives both pro and contra design inferences. Well-designed sections on design in general, physical cosmology, multiple universes, and biological considerations. Very helpful editor’s introduction rounds out an excellent volume.

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                            Ancestors of Anthropic Reasoning

                            Several appeals to observer-selection effects have predated the formulation of the anthropic principle, properly so-called. An important source is The Anthropic Cosmological Principle (Barrow and Tipler 1986, cited under General Overviews), which devotes two extensive chapters (2 and 3) to the teleological and design ancestors of anthropic argument, but the appeals to what we would now call “observer-selection effects” have an extensive history too. Balashov 1992 forges interesting connections between modern forms of anthropic reasoning and the place of the subject in transcendental philosophy. Bettini 2005 gives a very interesting historical survey, which reveals anthropic arguments to have had a longer pedigree than is often thought. Ćirković 2002 finds an interesting lesson for the modern debate on the apparent scarcity of extraterrestrial life in an early anthropic argument about the plane of cometary orbits that was formulated before Isaac Newton published his Principia. (It would seem Ćirković 2002 is correct in describing this argument as the first anthropic argument worthy of the name, Bettini 2005 notwithstanding.) Very likely the best work in this section is McMullin 1993, which combines a high degree of probabilistic competence with unusually generous amounts of historical knowledge, sensitivity, and insight—a work that deserves to be better known. Richmond 2000 contrasts various kinds of cyclical cosmology with 18th-, 19th-, and 20th-century attempts at extending evolutionary explanations to include the origins of the properties of matter. Roush 2003 is highly recommended reading, not the least for its combination of historical insight with applicable lessons for modern anthropic thinkers. Whitrow 1955 offers an interesting example of an anthropic argument from before such arguments were ever baptized—specifically, an attempted anthropic derivation of the dimensionality of space.

                            • Balashov, Yuri. “Transcendental Background to the Anthropic Reasoning in Cosmology.” Man and World 25 (1992):115–132.

                              DOI: 10.1007/BF01250531Save Citation »Export Citation »E-mail Citation »

                              Situates the anthropic debate in the context of historical discussions inspired by the transcendental philosophies of Immanuel Kant, Edmund Husserl, and Karl Jaspers. Usefully relates areas of philosophy not often joined in anthropic discussions. Available online by subscription.

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                              • Bettini, Steffano. “Anthropic Reasoning in Cosmology: A Historical Perspective.” In Formale Teleologie und Kausalität. Edited by Michael Stöltzner and Paul Weingartner. Paderborn, Germany: Mentis, 2005.

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                                Useful historical survey of the development of anthropic reasoning, particularly in cosmology. Highlights some underdiscussed and interesting references.

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                                • Ćirković, Milan. “On the First Anthropic Argument in Astrobiology.” Earth, Moon, and Planets 91 (2002): 243–254.

                                  DOI: 10.1023/A:1026266630823Save Citation »Export Citation »E-mail Citation »

                                  Explores Bernard Le Bouyier de Fontenelle’s 1686 argument for anthropic restrictions on cometary orbits, that comets’ tails would make life on Earth impossible if all cometary orbits were coplanar with those of the planets. Also considers the relevance of this argument to the frequency of extraterrestrial life.

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                                  • McMullin, Ernan. “Indifference Principle and Anthropic Principle in Cosmology.” Studies in History and Philosophy of Science, Part A 24.3 (1993): 359–389.

                                    DOI: 10.1016/0039-3681(93)90034-HSave Citation »Export Citation »E-mail Citation »

                                    Historically detailed and scientifically well-informed survey of the contrast between Copernican indifference (or mediocrity) conceptions and anthropic conceptions of our place in nature. Very good on particular inflation explanations for apparent fine-tuning.

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                                    • Richmond, Alasdair. “Epicurean Evolution and the Anthropic Principle.” American Philosophical Quarterly 37.2 (2000): 149–161.

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                                      Contrasts multiverse explanations for fine-tuning with the cyclical cosmos postulated by Epicurus and revived in David Hume’s Dialogues concerning Natural Religion (1779). Also considers T. H. Huxley’s and Karl Popper’s speculations on evolutionary processes governing the structure of matter.

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                                      • Roush, Sherrilyn. “Copernicus, Kant, and the Anthropic Cosmological Principles.” Studies in History and Philosophy of Science, Part B: Studies in History and Philosophy of Modern Physics 34.1 (2003): 5–35.

                                        DOI: 10.1016/S1355-2198(02)00029-1Save Citation »Export Citation »E-mail Citation »

                                        Argues for the essentially Copernican inspiration of anthropic thinking and that anthropic thinking is not in tension with any “principle of mediocrity.” Also argues that including observer-selection effects will in fact increase the objectivity of science rather than the reverse.

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                                        • Whitrow, G. J. “Why Physical Space Has Three Dimensions.” British Journal for the Philosophy of Science 6.21 (1955): 13–31.

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                                          Among other anthropic arguments about space, contains the intriguing suggestion that only spaces of three dimensions or more can support observers, because a conventional digestive tract through a two-dimensional animal would cut it in two. See also criticism in Smart 1987, cited under Critiques of Anthropic Reasoning). Available online by subscription.

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                                          The Anthropic Principle and Design Arguments

                                          Anthropic arguments have often gone hand in glove with arguments for a divine designer (see also Manson 2003, cited under Anthologies). However, the precise relationship between anthropic reasoning and design inferences is disputed. The strong anthropic principle (SAP) is often (mis)read as carrying teleological implications, that is, the universe must, in some categorical sense, have to produce life. Advocates and opponents of SAP have encouraged the idea that SAP is inevitably and inescapably teleological or design friendly. In fact, while SAP can be given a teleological or design orientation, many strongly teleological readings of SAP confuse categorical inferences with conditional ones. If I believe I breathe oxygen, I should believe it is likely there is oxygen in my immediate environment: it need not (although it might) be the case that nature has been rigged so that oxygen must be present to ensure my survival. Interestingly, while many critics of Barrow and Tipler 1986, (cited under General Overviews), take John D. Barrow and Frank J. Tipler to task for illicit teleological thinking, Craig 1988 criticizes them for failing to face up to the specifically design-centered implications of their arguments. Holder 2002 defends the choice between many-worlds and design explanations while offering cogent arguments to the effect that design is the more economical hypothesis of the two. Leslie 1992 is a useful guide, primarily aimed at those of biological expertise, to how philosophers have historically conceived of, and searched for, evidence of design. Leslie 1993 usefully contrasts theistic and atheistic conceptions of fine-tuning, with helpful thoughts on where the two approaches diverge. Leslie 2000 also defends the necessity to choose between either many-worlds or design hypotheses while offering suggestions for observational tests to distinguish between the two. Smith 1991 argues that attempts to justify teleological or cosmological arguments to deity based on big bang cosmology are at best inconclusive and that big bang cosmology if anything favors an atheistic worldview. Smith 1992 offers a highly provocative argument that the correct inference to draw from observed anthropic coincidences leads to conclusions that are deeply hostile (nay antithetical) to traditional conceptions of deity. Perhaps the most influential work under this heading, Swinburne 1990 is a classic statement of the argument from fine-tuning to design and one that is usefully underpinned by probabilistic argument.

                                          • Craig, William Lane. “Barrow and Tipler on the Anthropic Principle vs. Divine Design.” British Journal for the Philosophy of Science 39.3 (1988): 389–395.

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                                            Criticizes what Craig sees as the antitheistic emphasis of Barrow and Tipler 1986 (cited under General Overviews) and argues for design as a viable alternative to certain kinds of many-worlds explanations for anthropic coincidences and fine-tuning. Available online by subscription.

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                                            • Holder, Rodney D. “Fine-Tuning, Multiple Universes, and Theism.” Noûs 36.2 (2002): 295–312.

                                              DOI: 10.1111/1468-0068.00372Save Citation »Export Citation »E-mail Citation »

                                              Argues that only many-worlds or theism provide viable explanations for fine-tuning. Concludes that theism provides the better explanation of the two but argues en route that many-worlds can be a viable explanation for the fine-tuning of this universe. Available online by subscription.

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                                              • Leslie, John. “Design and the Anthropic Principle.” Biology and Philosophy 7.3 (1992): 349–354.

                                                DOI: 10.1007/BF00129975Save Citation »Export Citation »E-mail Citation »

                                                An introduction to anthropic thinking aimed primarily at the biologically trained, usefully distinguishing between anthropic and design approaches. Available online by subscription.

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                                                • Leslie, John. “Creation Stories, Religious and Atheistic.” International Journal for Philosophy of Religion 34.2 (1993): 65–77.

                                                  DOI: 10.1007/BF01317097Save Citation »Export Citation »E-mail Citation »

                                                  Contrasts theistic and anthropic (many-worlds) explanations for the apparent fine-tuning of the physical world. Available online by subscription.

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                                                  • Leslie, John. “Our Place in the Cosmos.” Philosophy 75.1 (2000): 5–24.

                                                    DOI: 10.1017/S0031819100000036Save Citation »Export Citation »E-mail Citation »

                                                    Usefully contrasts the weak anthropic principle (WAP) and the strong anthropic principle (SAP) while evaluating the competing merits of design and many-worlds explanations for fine-tuning. Offers suggestions for differing predictions these theories might make. Available online for purchase or by subscription.

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                                                    • Smith, Quentin. “Atheism, Theism, and Big Bang Cosmology.” Australasian Journal of Philosophy 69.1 (1991): 48–66.

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                                                      Aims to redress a perceived imbalance by offering a sustained account of big bang cosmology that is compatible with atheism but also argues for the incompatibility of theism with big bang cosmology. Usefully compares different kinds of cosmological origin hypotheses. Available online by subscription.

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                                                      • Smith, Quentin. “The Anthropic Coincidences, Evil, and the Disconfirmation of Theism.” Religious Studies 28.3 (1992): 347–350.

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                                                        Criticizes attempts, notably made by Richard Swinburne, to derive theistic conclusions from anthropic coincidences. Smith argues instead that anthropic considerations in effect invert traditional theodicy and support belief in a malevolent deity.

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                                                        • Swinburne, Richard. “Argument from the Fine-tuning of the Universe.” In Physical Cosmology and Philosophy. Edited by John Leslie, 154–173. New York: Collier Macmillan, 1990.

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                                                          Far-reaching attempt to weigh the evidence for fine-tuning and to marshal it in an attempt to argue to a divine designer.

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                                                          Testing Anthropic Arguments

                                                          Because the weak anthropic principle (WAP) is often interpreted as meaning that observers necessarily evolved where they evolved, it is often dismissed as a mere tautology and therefore devoid of any practical or scientific implications. Some scientists and philosophers have taken up this challenge and have proposed ways of deriving empirical predictions from WAP. Others (notably Leslie 1986, cited under General Overviews) argue that even tautologous statements can combine with empirical assumptions to generate surprising predictions. One perennial family of objections holds that anthropic reasoning is based on a mere tautology and thus cannot lead to testable predictions. In response to this “tautology” charge, Carter 1983 proposes an argument concerning the number of crucial steps that are necessary for advanced life-forms to evolve, noting that the length of time it took intelligent life to evolve on Earth is of the same (rough) order of magnitude as the age of the Earth. Carter argues that this apparent coincidence is explicable if in fact it normally takes longer for intelligent life to evolve than said life’s parent star can be life supporting, and hence that most species die out before achieving any degree of intelligence. Wilson 1994 takes profound issue with Brandon Carter’s conclusions and methods, whereas Watson 2008 both accepts and tries to extend Carter’s reasoning. In a fascinating discussion appended to Carter 1983, Carter makes his closest approximation in print to date to outlining and endorsing the so-called doomsday argument. Other suggestions for anthropic research programs include the dark-matter search proposed in Garriga and Vilenkin 2003 and the limited endorsement of anthropic predictions offered in Hogan 2000. Interestingly, Ćirković 2002 argues that anthropic predictions conflict with classical theory over the scale of entropy fluctuations.

                                                          • Carter, Brandon. “The Anthropic Principle and Its Implications for Biological Evolution.” Philosophical Transactions of the Royal Society of London, Series A, Mathematics and Physical Sciences 310.1512 (1983): 347–363.

                                                            DOI: 10.1098/rsta.1983.0096Save Citation »Export Citation »E-mail Citation »

                                                            Applies anthropic reasoning to our species’ evolutionary history and our place in it. Derives a “crucial steps” formula for the number of distinct evolutionary innovations in human evolution, which is then used to argue for the relative rarity of intelligent extraterrestrials. Appended discussion gestures toward the doomsday argument. Available online by subscription.

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                                                            • Ćirković, Milan. “Anthropic Fluctuations vs. Weak Anthropic Principle.” Foundations of Science 7.4 (2002): 453–463.

                                                              DOI: 10.1023/A:1020777630378Save Citation »Export Citation »E-mail Citation »

                                                              Discusses a conflict between classical Boltzmann-Schuetz models of large-scale entropy fluctuations and the predictions of the weak anthropic principle.

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                                                              • Garriga, Jaume, and Alexander Vilenkin. “Testable Anthropic Predictions for Dark Energy.” Physical Review D 67.4 (2003): 043503.

                                                                DOI: 10.1103/PhysRevD.67.043503Save Citation »Export Citation »E-mail Citation »

                                                                Offers several suggestions for anthropic solutions to physical problems (e.g., why we live close to the time when the impact of dark energy starts to predominate) and direct tests of anthropic predictions based on predicted behavior of dark energy (e.g., most civilizations evolve in galaxies with low redshifts).

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                                                                • Hogan, Craig J.s “Why the Universe Is Just So.” Reviews of Modern Physics 72.4 (2000): 1149–1161.

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                                                                  Argues for the predictive value of selected anthropic arguments but also argues that several apparent coincidences and physical values can be explained without reference to observer-selection effects. Available online by subscription.

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                                                                  • Watson, Andrew J. “Implications of an Anthropic Model of Evolution for Emergence of Complex Life and Intelligence.” Astrobiology 8.1 (2008): 175–185.

                                                                    DOI: 10.1089/ast.2006.0115Save Citation »Export Citation »E-mail Citation »

                                                                    Furthers Brandon Carter’s “crucial steps” formula (Carter 1983) by offering probabilities for each step in the evolution of intelligent observers. Argues that extending Carter’s formula thus favors the “rare earth” hypothesis, that only a fraction of planets will be Earth-like and support intelligent life. Available online by subscription.

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                                                                    • Wilson, Patrick A. “Carter on Anthropic Principle Predictions.” British Journal for the Philosophy of Science 45.1 (1994): 241–253.

                                                                      DOI: 10.1093/bjps/45.1.241Save Citation »Export Citation »E-mail Citation »

                                                                      Reply to Carter 1983. Argues that neither of Brandon Carter’s predictions regarding evolutionary timescales nor the crucial steps needed for the evolution of consciousness affords genuine opportunities for testing anthropic predictions. Available online by subscription.

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                                                                      Critiques of Anthropic Reasoning

                                                                      Anthropic reasoning has drawn forth a great deal of criticism of rather differing value and impact. Inevitably, some of the most significant criticisms deal not so much with anthropic reasoning per se as the alleged fine-tuning of cosmic parameters that anthropic reasoning is often invoked to explain. Hence, several of the works cited in this section are of great significance for anthropic reasoning, although not explicitly about the topic. Carlson and Olsson 1998 effectively claims that explanations for fine-tuning have arisen in advance of their having any clearly defined explanandum, while Colyvan, et al. 2005 usefully and thoroughly takes some unexamined probabilistic assumptions behind fine-tuning arguments to task. While generally far from enamored of anthropic reasoning, Earman 1987 is specifically critical of Barrow and Tipler 1986, The Anthropic Cosmological Principle (cited in General Overviews), and does much to disentangle certain confusions over categorical versus conditional inferences therein. Gardner 1986 is fun reading and should get an award for best (pseudo-) anthropic acronym to date, although its discussion takes it rather closer to parody than detailed refutation. Mosterín 2005 is a very pungent expression of the view that anthropic explanations are not scientific, novel, or intrinsically useful. Smart 1987 takes a generally skeptical line with anthropic reasoning but usefully criticizes some earlier attempts at taking observer-selection effects into account. Tipler 1986 provides a useful and detailed corrective to Gardner 1986. Wilson 1991 is a useful articulation of an oft-expressed reservation about anthropic thinking: that it starts from excessively anthropocentric assumptions.

                                                                      • Carlson, Erik, and Erik Olsson. “Is Our Existence in Need of Further Explanation?” Inquiry 41.3 (1998): 255–275.

                                                                        DOI: 10.1080/002017498321760Save Citation »Export Citation »E-mail Citation »

                                                                        Criticizes the need for any special explanation of the physical conditions that make evolution of intelligent life possible. Available online for purchase or by subscription.

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                                                                        • Colyvan, Mark, Jay L. Garfield, and Graham Priest. “Problems with the Argument from Fine Tuning.” Synthese 145.3 (2005): 325–338.

                                                                          DOI: 10.1007/s11229-005-6195-0Save Citation »Export Citation »E-mail Citation »

                                                                          Criticizes fallacious uses of probability theory, especially the invocation of boundary conditions, in standard presentations of the fine-tuning argument. Also criticizes retrenchment strategies for fine-tuning arguments, including moving to “ballpark” probabilities or abandoning probabilities altogether. Available online by subscription.

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                                                                          • Earman, John. “The SAP Also Rises: A Critical Examination of the Anthropic Principle.” American Philosophical Quarterly 24.4 (1987): 307–317.

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                                                                            A generally skeptical reading of the utility and scientific status of anthropic arguments in general, with particular criticism reserved for the participatory anthropic principle (PAP) and the final anthropic principle (FAP). Offers insightful remarks on, for example, disguised categorical readings of the strong anthropic principle (SAP).

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                                                                            • Gardner, Martin. “WAP, SAP, PAP, and FAP.” New York Review of Books 33.8 (1986): 22–25.

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                                                                              Skeptical review of Barrow and Tipler 1986 (cited in General Overviews), which often does scant justice to the detail and structure of the arguments John D. Barrow and Frank J. Tipler put forward but is at least notable for coining that oft-cited parody, the “completely ridiculous anthropic principle.” Received a pungent reply in Tipler 1986. Available online by subscription.

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                                                                              • Mosterín, Jesús. “Anthropic Explanations in Cosmology.” In Logic, Methodology, and Philosophy of Science: Proceedings of the 12th International Congress. Edited by Petr Hájek, Luis Valdés-Villanueva, and Dag Westerståhl. London: King’s College, 2005.

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                                                                                Argues that, philosophical and scientific protestations notwithstanding, the anthropic principle is tautologous and therefore unscientific after all. Furthermore, claims for a new kind of explanation in cosmology, based on anthropic reasoning, are misplaced.

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                                                                                • Smart, J. “Philosophical Problems of Cosmology.” Revue Internationale de Philosophie 160 (1987): 112–126.

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                                                                                  Surveys a number of cosmological problems in philosophy. In the course of discussing a number of anthropic arguments, criticizes the Whitrow 1955 (cited under Ancestors of Anthropic Reasoning) derivation of the dimensionality of space from, for example, facts about mammalian digestive structure.

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                                                                                  • Tipler, Frank J. “The FAP Flop.” New York Review of Books 33.8 (1986).

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                                                                                    Letter-length reply to Gardner 1986 that draws attention to several subtleties of argument regarding the motivations and predictive resources of anthropic reasoning that Gardner seemingly missed. Also useful for its distinctions between different predictions derived from weak anthropic principle (WAP) and strong anthropic principle (SAP).

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                                                                                    • Wilson, Patrick A. “What Is the Explanandum of the Anthropic Principle?” American Philosophical Quarterly 28.2 (1991): 167–173.

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                                                                                      Argues that anthropic explanations of fine-tuning suffer from a built-in anthropocentric and teleological bias.

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                                                                                      Anthropic Reasoning, Quantum Theory, and Evolution

                                                                                      Two potentially fascinating areas of overlap between anthropic reasoning and particular scientific theories concern anthropic reasoning in quantum theory and evolutionary biology. Brandon Carter has made significant contributions to both fields. (See also the citations under Testing Anthropic Arguments.) Carter 1989 and Carter 1993 argue in depth for the compatibility of Darwinian and anthropic ideas, with Carter 1989 treating anthropic thinking as a plausible extension of Darwinian ideas and Carter 1993 relating anthropic explanations specifically to the revolution in Darwinian understanding brought about by advances in genetics and informatics. Carter 2004 and Carter 2007 tackle aspects of the quantum measurement problem from an anthropic perspective, in both cases arguing that anthropic ideas can solve problems bequeathed by Hugh Everett’s many-worlds approach. Leslie 1996 interestingly deploys the doomsday argument as a problem for the integrity and survival of observers in Everett’s multiverse. Linde 2004 makes a thoroughgoing attempt at offering distinct observational predictions for inflationary cosmology scenarios derived from the weak anthropic principle (WAP) and the strong anthropic principle (SAP).

                                                                                      • Carter, Brandon. “The Anthropic Principle: Self-Selection as an Adjunct to Natural Selection.” In Cosmic Perspectives: Essays Dedicated to the Memory of M. K. V. Bappu. Edited by S. K. Biswas, D. C. V. Mallik, and C. V. Vishveshwara, 185–206. Cambridge, UK: Cambridge University Press, 1989.

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                                                                                        Argues for the application of anthropic ideas as a natural extension of principles developed in considering evolution as the product of natural selection. A useful counterweight to more teleologically inspired readings of anthropic reasoning.

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                                                                                        • Carter, Brandon. “The Anthropic Selection Principle and the Ultra-Darwinian Synthesis.” In The Anthropic Principle. Edited by F. Bertola and U. Curi, 33–66. Cambridge, UK: Cambridge University Press, 1993.

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                                                                                          Argues for the mutual support and intelligibility of anthropic ideas and later Darwinian thinking, especially as the latter has developed in the light of modern genetics and computing.

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                                                                                          • Carter, Brandon. “Anthropic Interpretation of Quantum Theory.” International Journal of Theoretical Physics 43.3 (2004): 721–730.

                                                                                            DOI: 10.1023/B:IJTP.0000048171.28027.beSave Citation »Export Citation »E-mail Citation »

                                                                                            Argues against both Everett’s interpretation and any reintroduction of determinism or objectivity on a cosmological scale by proposing instead a weighted subjective probability measure, in turn based on an entropy principle that was derived from, but ultimately supersedes, WAP. Available online by subscription.

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                                                                                            • Carter, Brandon. “Micro-Anthropic Principle for Quantum Theory.” In Universe or Multiverse? Edited by Bernard Carr, 285–320. Cambridge, UK: Cambridge University Press, 2007.

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                                                                                              Argues that the objectivity problem introduced by the Copenhagen interpretation is not resolved by Everett’s many-worlds hypothesis. Proposes an answer to the “objectivity” problem that distinguishes between an observer and a perceptor, the latter standing to the former in a relation determined by a “micro” anthropic principle weighting (proportional to the logarithm of the number of relevant Everett branches).

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                                                                                              • Leslie, John. “A Difficulty for Everett’s Many-Worlds Theory.” International Studies in the Philosophy of Science 10.3 (1996): 239–246.

                                                                                                DOI: 10.1080/02698599608573542Save Citation »Export Citation »E-mail Citation »

                                                                                                Applies Brandon Carter and Leslie’s doomsday reasoning against Everett’s many-worlds theory, arguing that Everett’s theory means the vast majority of observer versions would exist in the interval immediately before extinction. Everett’s hypothesis therefore needs some mechanism whereby observer versions can diverge but without thereby becoming more numerous. Available online by subscription.

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                                                                                                • Linde, A. “Inflation, Quantum Cosmology, and the Anthropic Principle.” In Science and Ultimate Reality: Quantum Theory, Cosmology, and Complexity. Edited by John D. Barrow, Paul C. W. Davies, and Charles L. Harper Jr., 426–458. Cambridge, UK: Cambridge University Press, 2004.

                                                                                                  DOI: 10.1017/CBO9780511814990Save Citation »Export Citation »E-mail Citation »

                                                                                                  Argues for the scientific status of both WAP and SAP by relating the former to the predictions of inflationary cosmology and the latter to differing kinds of many-worlds (or multiverse) hypotheses.

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                                                                                                  The Inverse Gambler’s Fallacy

                                                                                                  Baptized in Hacking 1987, the inverse gambler’s fallacy denotes a fallacious form of probabilistic reasoning whereby a large number of previous operations are invoked to make a given outcome appear less improbable. An example would be someone entering a room wherein a coin has just been tossed and landed heads, and thereby concluding that the observed throw must be merely the last in a long series of trials. Hacking 1990 situates the inverse gambler’s fallacy in the context of probabilistic fallacies generally. Hacking 1987 uses this fallacy to drive a wedge between different kinds of explanation for fine-tuning. In particular, Hacking argues that using fine-tuning to support a John A. Wheeler oscillating (big bang/big crunch) cosmos commits the inverse gambler’s fallacy, whereas fine-tuning argument to a Hugh Everett branching-worlds universe does not. Specifically, Ian Hacking discusses a multiverse hypothesis that he attributes to Brandon Carter, whereby every logically possible universe compatible with big bang cosmology enjoys concrete existence. Thus, Hacking concludes, inferences to many simultaneous worlds from fine-tuning may succeed, but inferences to many successive worlds fail through fallacious probabilistic reasoning. While most commentators agree that the inverse gambler’s fallacy is indeed fallacious, they differ sharply over the soundness of its use in Hacking’s attempt in Hacking 1987 to discriminate between different explanations of fine-tuning. Dowe 2000 and White 2000 arrive at similar conclusions regarding the formal import of Hacking’s argument, that the successive and simultaneous world ensembles Hacking discusses are symmetrically affected by the inverse gambler’s fallacy, and both reject the pair of multiverse explanations concerned as failing to make fine-tuning probable. Juhl 2005, Leslie 1988, McGrath 1988, and Whitaker 1988 offer various diagnoses of where Hacking may have erred in using the inverse gambler’s fallacy to attack Wheeler explanations for fine-tuning. Although not directly about the inverse gambler’s fallacy, Juhl 2006 is a very interesting critique of fine-tuning arguments in general that usefully supplements the debate about the inverse gambler’s fallacy.

                                                                                                  • Dowe, Phil. “The Inverse Gambler’s Fallacy Revisited: Explanations of Fine Tuning.” Unpublished manuscript, 2000.

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                                                                                                    Rejects the Hacking 1987 diagnosis that Wheeler cycles and Carter multiverses are asymmetrical when it comes to fine-tuning but argues that both theories fail to explain why this universe should happen to be fine-tuned.

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                                                                                                    • Hacking, Ian. “The Inverse Gambler’s Fallacy: The Argument from Design; The Anthropic Principle Applied to Wheeler Universes.” Mind 96.383 (1987): 331–340.

                                                                                                      DOI: 10.1093/mind/XCVI.383.331Save Citation »Export Citation »E-mail Citation »

                                                                                                      Introduces the inverse gambler’s fallacy. Claims that arguments invoking Wheeler oscillating universes and Everett branching universes to explain fine-tuning differ markedly in success, with the former failing through committing the hitherto-undiagnosed probabilistic fallacy referred to in the paragraph introducing this section. Available online by subscription.

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                                                                                                      • Hacking, Ian. The Taming of Chance. Cambridge, UK: Cambridge University Press, 1990.

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                                                                                                        Monograph-length work on probability that also covers the inverse gambler’s fallacy in greater depth.

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                                                                                                        • Juhl, Cory. “Fine-tuning, Many Worlds, and the Inverse Gambler’s Fallacy.” Noûs 39.2 (2005): 337–347.

                                                                                                          DOI: 10.1111/j.0029-4624.2005.00504.xSave Citation »Export Citation »E-mail Citation »

                                                                                                          Agrees that Ian Hacking has correctly diagnosed a fallacy but argues that he has incorrectly related certain many-worlds arguments to these fallacies. In particular, the validity of these inferences varies sharply with the background assumptions in use. Available online by subscription.

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                                                                                                          • Juhl, Cory. “Fine-tuning Is Not Surprising.” Analysis 66.292 (2006): 269–275.

                                                                                                            DOI: 10.1111/j.1467-8284.2006.00628.xSave Citation »Export Citation »E-mail Citation »

                                                                                                            Argues that fine-tuning arguments often fail to distinguish between evidence that human beings are causally ramified and evidence that the laws of nature were set up to favor the existence of human beings. Available online by subscription.

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                                                                                                            • Leslie, John. “No Inverse Gambler’s Fallacy in Cosmology.” Mind 97.386 (1988): 269–272.

                                                                                                              DOI: 10.1093/mind/XCVII.386.269Save Citation »Export Citation »E-mail Citation »

                                                                                                              Argues that neither Wheeler’s nor Carter’s explanation falls foul of the inverse gambler’s fallacy. Also offers useful pointers on what the explanandum of fine-tuning arguments is supposed to be. Available online by subscription.

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                                                                                                              • McGrath, P. J. “The Inverse Gambler’s Fallacy and Cosmology: A Reply to Hacking.” Mind 97.386 (1988): 265–268.

                                                                                                                DOI: 10.1093/mind/XCVII.386.265Save Citation »Export Citation »E-mail Citation »

                                                                                                                Accepts that the inverse gambler’s fallacy is genuinely fallacious but argues that Ian Hacking’s argument does not establish any Wheeler/Everett asymmetry and fails to take proper account of observer-selection effects. Available online by subscription.

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                                                                                                                • Whitaker, M. A. B. “On Hacking’s Criticism of the Wheeler Anthropic Principle.” Mind 97.386 (1988): 259–264.

                                                                                                                  DOI: 10.1093/mind/XCVII.386.259Save Citation »Export Citation »E-mail Citation »

                                                                                                                  Attacks the assumptions of sampling independence behind Ian Hacking’s analogy between the inverse gambler’s coin toss and the Wheeler cyclical cosmos (Hacking 1987). Available online by subscription.

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                                                                                                                  • White, Roger. “Fine-tuning and Multiple Universes.” Noûs 34 (2000): 260–276.

                                                                                                                    DOI: 10.1111/0029-4624.00210Save Citation »Export Citation »E-mail Citation »

                                                                                                                    Besides arguing that fine-tuning does not raise the probability that there are many worlds, argues that Hacking 1987 is successful not only against a Wheeler successive (or oscillating) many-worlds system but also against a Carter (or nonsuccessive) many-worlds system. Available online by subscription.

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                                                                                                                    The Doomsday Argument

                                                                                                                    Perhaps one of the most lively and provocative offshoots of anthropic reasoning is the somewhat misleadingly named “doomsday argument.” In essence, the doomsday argument says that applying anthropic notions of typicality to our location in human history (combined with some plausible Bayesian assumptions about how to accord likelihoods to our birth rank) yields the remarkable conclusion that we should raise our probability for imminent human extinction. The doomsday debate began with a discussion after a lecture on testable implications of anthropic reasoning by Brandon Carter, some of which appears as an appendix to Carter 1983 (cited under Testing Anthropic Arguments). Carter has yet to discuss doomsday reasoning in print, so the bulk of initial expositions were produced by John Leslie; hence, the argument is often dubbed the “Carter-Leslie doomsday argument.” Leslie 1992 arrives at doomsday conclusions by applying anthropic principles to our observed location in time. Gott 1993 and Gott 1994 outline a different but related route to doomsday conclusions that invokes the Copernican principle of mediocrity. A very full discussion of doomsday is the subject of Leslie 1996 (chapters 5 and 6). Bartha and Hitchcock 1999 clearly outlines a popular riposte to doomsday reasoning, that favoring explanations that make our existing at all more probable produces a probability shift in favor of larger populations that exactly counterbalances the doomsday shift. However, see Bostrom 1999 for searching critiques of this and other popular doomsday rebuttals. Richmond 2006 tries to survey all of the work in the doomsday field, concentrating specifically on the Carter-Leslie and Gott-Bayesian versions but also taking in some other anthropic theories about the likelihood of human extinction. Sober 2003 is interesting for offering a consistent set of probabilistic objections to both the Carter-Leslie and Gott formulations. Eastman 2002 offers a remarkable series of speculations driven by doomsday reasoning that include a novel argument against determinism.

                                                                                                                    • Bartha, Paul, and Christopher Hitchcock. “No One Knows the Date or the Hour: An Unorthodox Application of Rev. Bayes’s Theorem.” Philosophy of Science 66.3 (1999): S339–S353.

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                                                                                                                      Argues that doomsday conclusions can be avoided or defused if we take into account the probability of our own existence.

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                                                                                                                      • Bostrom, Nick. “The Doomsday Argument Is Alive and Kicking.” Mind 108.431 (1999): 539–550.

                                                                                                                        DOI: 10.1093/mind/108.431.539Save Citation »Export Citation »E-mail Citation »

                                                                                                                        Argues that while doomsday arguments use a questionable set of sampling assumptions (and thus their conclusions are ultimately resistible), nonetheless the inference involved is more robust than many critics allow. Very handy primer on the failure of some supposedly obvious and decisive doomsday refutations. Available online by subscription.

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                                                                                                                        • Eastman, John F. G. “The Doomsday Argument, Consciousness, and Many Worlds.” August 2002.

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                                                                                                                          Argues that doomsday reasoning can be reformulated to show that there is no possibility of an infinite, conscious lifetime, on pain of otherwise generating contradictions. Very wide-ranging series of doomsday-inspired speculations on consciousness, quantum theory, and determinism.

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                                                                                                                          • Gott, J. Richard, III. “Implications of the Copernican Principle for our Future Prospects.” Nature 363 (1993): 315–319.

                                                                                                                            DOI: 10.1038/363315a0Save Citation »Export Citation »E-mail Citation »

                                                                                                                            First appearance in print of J. Richard Gott III’s Copernican version of doomsday reasoning, based on the idea that, all else being equal, we should have 95 percent confidence that we are encountering a given phenomenon at a time outside the first or last 5 percent of its existence. Available online for purchase or by subscription.

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                                                                                                                            • Gott, J. Richard, III. “Future Prospects Discussed: Gott Replies.” Nature 368.6467 (1994): 108.

                                                                                                                              DOI: 10.1038/368108a0Save Citation »Export Citation »E-mail Citation »

                                                                                                                              Reply to a mixed bag of criticisms of Gott 1993, offering further applications of the original argument. Available online for purchase or by subscription.

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                                                                                                                              • Leslie, John. “Time and the Anthropic Principle.” Mind 101.403 (1992): 521–540.

                                                                                                                                DOI: 10.1093/mind/101.403.521Save Citation »Export Citation »E-mail Citation »

                                                                                                                                In part inspired by issues raised in Carter 1983 (cited under Testing Anthropic Arguments), applies anthropic reasoning to our likely location in the lifetime of our species. An important precursor of later doomsday discussions. Available online by subscription.

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                                                                                                                                • Leslie, John. The End of the World: The Science and Ethics of Human Extinction. London: Routledge, 1996.

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                                                                                                                                  Primarily devoted to enumerating threats to human survival but also contains, in its fifth and sixth chapters, a detailed statement of the Carter-Leslie doomsday argument, a useful survey of “obvious” ripostes to it, and suggestions for testing it.

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                                                                                                                                  • Richmond, Alasdair M. “Recent Work: The Doomsday Argument.” Philosophical Books 47.2 (2006): 129–142.

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                                                                                                                                    Survey article covering the Carter-Leslie, Gott, and other incarnations of doomsday reasoning. Also looks at non-Bayesian arguments concerning human extinction and their relations to anthropic reasoning. Available online by subscription.

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                                                                                                                                    • Sober, Elliot. “An Empirical Critique of Two Versions of the Doomsday Argument: Gott’s Line and Leslie’s Wedge.” Synthese 135.3 (2003): 415–430.

                                                                                                                                      DOI: 10.1023/A:1023545820214Save Citation »Export Citation »E-mail Citation »

                                                                                                                                      Searching critique of the empirical and probabilistic assumptions behind the two most popular doomsday formulations. Argues that there is no generally applicable doomsday inference. Available online for purchase or by subscription.

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                                                                                                                                      The Simulation Argument

                                                                                                                                      Inspired by (but crucially different from) doomsday reasoning, Nick Bostrom’s simulation argument is a startling application of anthropic (or, more accurately, observer-selection) reasoning. Bostrom argues that functionalism about the mind combined with certain Bayesian principles and some plausible assumptions about the potential growth of computing power should incline us to favor the hypothesis that we currently inhabit a computer simulation of reality. Or, to offer the disjunctive version of Bostrom’s conclusions, certain functionalists should distribute their credences between three hypotheses: (a) advanced (“posthuman”) civilizations are rare, (b) posthumans simulate few minds, or (c) we are probably now simulations ourselves. Needless to say, most commentators have leapt on Bostrom as though he sought to defend point (c), when in fact Bostrom is concerned only with defending the three-way disjunction. The simulation argument was first stated in Bostrom 2001 and then refined and expanded in Bostrom 2003. Although Brueckner 2008 receives a thorough rebuttal in Bostrom 2009, it retains value as a statement of one of the most commonly urged objections to the simulation argument. Bostrom 2009 is essential reading for anyone who would criticize the simulation argument. Weatherson 2003 usefully criticizes the simulation argument by criticizing its epistemic assumptions—assumptions that Bostrom 2005 defends.

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