The anthropic principle and its implications for biological evolution

“Carter (1974, 1976, 1983), who actually coined the term “anthropic principle”, showed that the numerological coincidence found by Dirac can be derived from physical models of stars and the competition between the weakness of gravity with respect to nuclear fusion.”

“Nonetheless, given the present stage of understanding and lack of data, the possibilities for P(life jEarth-like) range from life being very common to very rare, as has been much discussed in the literature (e.g., Carter, 1983; Spiegel and Turner, 2012; Scharf and Cronin, 2016; Walker, 2017).”

“Indeed, it has been argued that if intelligent life requires a great deal of time to evolve, Earth may be a rare planet, on which life got started unusually early (Carter, 1983).”

“The probabilistic anthropic model of Watson (2008), which draws on the theory of critical evolutionary transitions advanced by Szathma´ry and Maynard-Smith (1995) and the ‘‘critical steps’’ model of Carter (1983), proposes that complex biology becomes increasingly probable with longer HZ life-times.”

“We note several previous quantitative attempts to address this issue in the literature, of which one [8] found, as we do, that early abiogenesis is consistent with life being rare, and the other [9] found that Earth’s early abiogenesis points strongly to life being common on Earth-like planets (we compare our approach…”

“Carter (1983) has pointed out that the time scale for the evolution of intelligence on the Earth ( , 5 Gyr) is comparable to the main sequence lifetime of the Sun ( , 10 Gyr).”

“Attempts have been made to estimate P(life) within a Bayesian framework by Carter and McCrea (Carter and McCrea, 1983) and more recently by Spiegel and Turner (Spiegel and Turner, 2012).”

“Maximum τhab is greatly increased (Carter 1983).”

“In addition (1983) suggested an independent life on Earth in the galactic context generally recognized that “contact pes-simists” a strong position.”

“Our results provide a new perspective on the so-called “coincidence problem”, why do we observe Ωm ∼ ΩΛ? [37] The answer comes naturally if we consider the history of Sun-like star formation, as the number of habitable planets peaks around present time for m ∼ 1M .”

“In addition, we have witnessed substantial research leading to a decrease in confidence in the so-called Carter’s (1983) ”anthropic” argument, the other mainstay of SETI scepticism (Wilson 1994; Livio 1999; Ćirković and Dragićević 2006, preprint).”

“The distinction between the ‘hard’ and the ‘easy’ formation of early life can be highlighted by the adaptation of the Carter formula (Carter 1983; Barrow & Tiepler 1988) and its slight extension ( Jortner 2006, unpublished results).”

“Although anthropic arguments have been put forth with a range of definitions (classic references include [61, 122, 131, 132]), the basic consideration is that the universe must have the proper version of physical law in order to develop observers.”

“3 But see e.g. (Carter 1983, 1989; Bostrom 2002a; Hanson 1998b). extinction of the human species.”

“One reason for this may be the conclusion originally reached by Carter (1983), that there was only 1 such step or, at most, 2, based on the assumption that we are presently only midway through the life span of the biosphere.”

“Lastly, some believe that tens to hundreds of millions of years would be needed for nature to survey nonfunctional biopolymer sequence space in order to form macromolecules on prebiotic Earth (e.g., Carter 1983; Neveu et al. 2013; Adamala et al. 2014).”

“ar X iv :g rqc /0 00 90 81 v2 1 3 O ct 2 00 0 If the human race comes to an end relatively shortly, then we have been born at a fairly typical time in history of humanity.”

“The aim of the present discussion is to clarify the problem of identifying which of the essential steps may have been hard in the sense Carter (1983) of depending on the fortuitous occurrence of some combination of random events that would automatically happen sooner or later if unlimited time were…”

“…assumes that it typically takes several billion years for intelligent life to arise (some 4.5 Gyr in the case of humans,and please note that the Carter (1983) argument suggests that the typical timescale may be much longer than this), then only the z 2 part of the universe becomes relevant.”

“Carter (1983) noticed this coincidence and proposed a resolution to the puzzle based on observation selection effects.”

“A more recent version known as the “doomsday argument” implies that we might be much closer to the end of civilization than to its beginning due to the probabilistic implications of this growth (Carter and McCrea 1983; Bostrom 2013) or more broadly from the Copernican principle (Gott 1993).”

“One objection is the famous “Doomsday argument” (Carter 1983; Leslie 1990; see also Bostrom 2002, pp. 89ff. and references therein).”

“…just “civilisations”) is famously uncertain, with estimates of the civilisation incidence per habitable planet ranging from 10−5 (Sagan 1963) to arbitrarily small values (e.g., < 10−30, combining pessimistic estimates from Carter 1983; Ward & Brownlee 2000; Schermer 2002; Spiegel & Turner 2012).”

“As noted by Carter and McCrea [10] the evidential power of the early emergence of life on Earth is weakened by observer selection effects, allowing for deep uncertainty about what the natural timescale of life formation is.”

“An example is the so-called doomsday argument (Carter and McCrea 1983), which holds that there is a high probability that humanity will be extinct (or will drastically reduced in population) soon, because if this were not true—if, for example, humanity were to continue with 10 billion people or so for the next few tho…”

“These other forms of reasoning include methods of deriving observational consequences from cosmological models (Leslie 1989; Bostrom 2000b; Bostrom 2001a), arguments concerning how improbable was the evolution of intelligent life on Earth (Carter 1983; Carter 1989), and game theoretic problems involving imperfect reca…”

“Age If the evolution of observers like ourselves takes on average many billions of years, we might expect the Sun to be anomalously old (Carter 1983).”

“The likelihood of epoch (21)The number of these transitions that led to noogenesis (the emergence of intelligence) on Earth remains unsettled, but has been suggested to lie between 4 and 7 by several authors (Carter, 1983; Watson, 2008; Carter, 2008; McCabe and Lucas, 2010); see also: http://mason.”

“The Doomsday argument, based on a priori estimates of the total number of humans that will come to be over time, also leads to high belief in human extinction.(45,46) It is not clear that these suppositions support the converse, that human survival is likely, so this element of the frame of discernment received no pro…”

“This situation was considered by Carter (1983), who used it to explain why, to within a factor of about 2, the time taken for evolution to produce intelligence on Earth is the same as the expected lifetime of the main sequence stage of the sun (alternatively, the duration of habitability of the…”

“We conclude that even the simplest preliminary models show it is too early to draw sceptical conclusions about the abundance of extraterrestrial life and intelligence from our single data point via the ”anthropic” argument of Carter (1983).”

“The Doomsday Argument was conceived by the astrophysicist Brandon Carter some fifteen years ago [i.e. Carter 1983], and it has since been developed in a Nature article by Richard Gott (1993), and in several papers by philosopher John Leslie and especially in his recent monograph The End of The World (Leslie 1996).”

“Watson (2008), drawing on the earlier work of Carter (1983) and Szathma´ry and Maynard-Smith (1995), developed a probabilistic model that attempts to quantify the timing and likelihood of several critical (de-fined broadly as only occurring once in Earth’s history) steps in evolution en route to…”

“Hence, a planet that does not pass through a series of complex evolutionary steps will be incapable of giving rise to intelligence (Carter 1983; Watson 2008).”

“And, the future generations are many (Brandon Carter, 1983; Leslie, 1998).”

“As shown in Carter (1983), if there are n critical steps leading to some property such as intelligence or technological capability and each kth step has low probability lk (lkth 1), then the expectation for the time at which the kth step will occur is htk=ni ¼ k n þ 1 th (2) Using a more detailed…”

“In this paper, we will therefore use a model originally developed by Carter (1983), where evolution is treated as a succession of critical steps, to assess the likelihood of primitive (microbial) and intelligent (technological) life, and the implications for detecting biosignatures and…”

“We conclude that it is too early to draw skeptical conclusions about the abundance of extraterrestrial life and intelligence from our single data point via the ‘‘anthropic’’ argument of Carter (1983).”

“The example that seems to me most important was provided by the prediction [9] that the occurrence of anthropic observers would be rare, even on environmentally favorable planets such as ours.”

“213 The analogy between black hole mechanics and thermodynamics was spelled out in Bardeen, Carter, and Hawking (1973).”

“Carter’s anthropic argument (Carter 1983, 1993, Livio 1999): If biological and astrophysical timescales determining the evolution of life and intelligence are independent, we have a posteriori Bayesian reasons to believe that the biological timescale is much larger than the astrophysical one, thus…”

“As a result, the fiducial time scale of 1 Gyr, while appropriate for life on Earth, does not represent a definitive limit.”

“The number of steps discussed in the literature varies between two (Carter 1983) and ten (Barrow & Tipler 1986), and the mean interval between steps can be interpreted in the context of major evolutionary stages, such as biogenesis, bacterial, eukaryotes, combigenesis, metazoans, and civilization…”

“If we assume the self-sampling assumption(7, 8), essentially that we expect to find ourselves in one of the universes with greatest measure, subject to the constraints of the anthropic principle.”

“From this observation, there have been numerous efforts to quantify k conditioned upon this datum, with, for example, Carter (1983) concluding that it is compatible with life being rare, whereas the findings of Line-weaver and Davis (2002) point strongly toward life being common on Earth-like worlds.”

“This author, however, finds his arguments compelling, and interested readers are advised to read the works of Carter (1983) and Watson (2008) if they require further reassurance.”

“Wheeler thereby evidently became an early advocate of the “Participatory Anthropic Principle” as primarily put forward by Brandon Carter (1983) and later by Robert Dicke (1961), indicating that the laws of physics are fine-tuned to permit the existence of life (see for a review of anthropic factors, Ross, 1989).”

“A simple stochastic model, first proposed by Carter (1983) and discussed by Barrow & Tipler (1986), Hanson (1998) and Flambaum (2003), assumes that evolution is governed by a series or critical transitions or bottlenecks, which must be passed to advance from basic molecules to simple, complex and…”

“…might arise from simple dead matter, via intermediate steps of simple life, complex life, etc., a model that he and many others have since pursued (Carter 1983; Caldeira & Kasting 1992; Hanson 1998b; Carter 2008; Watson 2008; McCabe & Lucas 2010; Aldous 2012; Simpson 2017; Waltham 2017; Sandora…”

“Carter (1983) has pointed out that the timescale for the evolution of intelligence on the Earth (*5 Gyr) is comparable with the main sequence lifetime of the Sun (*10 Gyr).”