Cosmological natural selection (fecund universes)
Cosmological natural selection (CNS), also known as fecund universes, is a prominent theory of universe evolution, development and reproduction originally proposed by eminent theoretical physicist and quantum gravity scholar Lee Smolin in 1992.
Universe reproduction via black holes
According to CNS, black holes may be mechanisms of universe reproduction within the multiverse, an extended cosmological environment in which universes grow, die, and reproduce. Rather than a ‘dead’ singularity at the center of black holes, a point where energy and space go to extremely high densities, what occurs in Smolin’s theory is a 'bounce' that produces a new universe with parameters stochastically different from the parent universe. Smolin theorizes that these descendant universes will be likely to have similar fundamental physical parameters to the parent universe (such as the fine structure constant, the proton to electron mass ratio and others) but that these parameters, and perhaps to some degree the laws that derive from them, will be slightly altered in some stochastic fashion during the replication process. Each universe therefore potentially gives rise to as many new universes as it has black holes.
In a process analogous to Darwinian natural selection, those universes best able to reproduce and adapt would be expected to predominate in the multiverse. As with biological natural selection, mechanisms for reproduction, variation, and the phenotypic effects of alternate parameter heritability may be modeled. With respect to adaptation, selection for a range of proposed universal fitness functions (black hole fecundity, universal complexity, etc.) may be tentatively tested with respect to present physical theory, by exploring the features with respect to these functions of the ensemble of possible universes that are adjacent to our universe in parameter space. Nevertheless, strategies for validating the appropriateness of fitness functions remain unclear at present, as do any hypotheses of adaptation with respect to the multiverse, other universes, or other black holes.
Smolin states that CNS originated as an attempt to explore the fine-tuning problem in cosmology via an alternative landscape theory to string theory, one that might provide more readily falsifiable predictions. According to The Life of the Cosmos (1997), his book on CNS and other subjects for lay readers, by the mid-1990’s his team had been able to sensitivity test, via mathematical simulations, eight of approximately twenty apparently fundamental parameters. In such tests to date, Smolin claims our present universe appears to be fine-tuned both for long-lived universes capable of generating complex life and for the production of hundreds of trillions of black holes, or for ‘fecundity’ of black hole production.
His theory has been critiqued on occasion (Vaas 1998; Vilenkin 2006), and continues to be elaborated and defended (Smolin 2001,2006). McCabe (2006) states that research in loop quantum gravity “appears to support Smolin’s hypothesis” of a bounce at the center of black holes forming new universes (see also Ashtekar 2006). If true, such a mechanism would suggest an organic type of reproduction with inheritance for universes, and the universe ensemble might be characterized as an extended, branching chain exploring a ‘phenospace’ of potential forms and functions within the multiverse.
Antecedents to CNS
In an update of the oscillating universe model of Alexander Friedman (1922), John A. Wheeler (1973,1977) proposed that the basic laws and constants of the universe might fluctuate randomly to new values at each successive bounce (new universe birth), and thus provide a natural mechanism for anthropic selection. Though Wheeler's and others' original oscillation models did not survive criticism, oscillating universe theory has been revived by some theorists as the cyclic model in brane cosmology, yet remains controversial as it presently offers no satisfactory description of the bounce via string theory. Furthermore, recent empirical evidence that universal expansion is not slowing but is accelerating (observation of distant supernovae as standard candles, and the mapping of the cosmic microwave background), would argue that a future Big Crunch is unlikely. Nevertheless, an oscillating model cannot yet be ruled out entirely as the nature and future dynamics of the dark energy that drives universal acceleration is not yet known.
Beginning in the 1980’s theorists in quantum gravity began postulating that our universe might ‘give birth’ to new universes via fluctuations in spacetime over very short distances (Baum 1983; Strominger 1984; Hawking 1987,1988,1993; Coleman 1988). Some theorists (Hawking 1987; Frolov 1989) proposed that new universe creation might be particularly likely in the singularity region inside black holes.
As Victor J. Stenger observes (1999), prior to Smolin's 1992 article Quentin Smith (1990) independently proposed that random symmetry breaking events in the initial Big Bang singularity, and in black hole singularities that form in universes of our type, might lead to the production of new universes via black holes, and this could provide a naturalistic explanation for the emergence of the basic laws and constants of our universe.
Extensions of CNS
Crane's Meduso-anthropic principle first proposed (in an arxiv.org preprint in 1994) including intelligence in the CNS process, which we may call "CNS-I". Cosmologist Edward Harrison (1995) independently proposed that the purpose of intelligent life is to produce successor universes, in a process driven by natural selection at the universal scale. Harrison's work was apparently the first CNS-I hypothesis to be published in a peer-reviewed journal.
James N. Gardner (2000,2003,2007) has explored CNS-I ideas at length with his Selfish biocosm hypothesis. Smart (2000,2008) has also extensively explored CNS-I consequences and ramifications via an evo devo universe hypothesis. Inspired by Lloyd (2000), he proposes a constrained developmental destiny for all universal intelligence in the form of black hole computational entities, in his developmental singularity hypothesis. He considers intelligence-mediated universal selection as a form of niche construction, after Odling-Smee (2003), and envisions very limited capacity for evolutionary intelligence to alter universal developmental parameters in each replication cycle, as with biological life. For Vidal (2008, 2009), an intervention of intelligence in the universal reproduction process would be appropriately named "Cosmological Artificial Selection". In this scenario, a cosmic blueprint would be artificially fine-tuned by intelligence. The selection process would then not be random or natural, but mediated by intelligence, or artificial.
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