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 our universe ensemble might be characterized as an extended, branching chain exploring a ‘phenospace’ of potential forms and functions within the multiverse.
Antecedents to CNS
The earliest antecedent to CNS may have been the oscillating universe model of Alexander Friedman (1922). Another oscillating model was the phoenix universe of Georges Lemaître (1933). In 1973 and 1977, John A. Wheeler proposed that the basic laws and constants of the universe might fluctuate randomly to new values at each successive bounce (new universe birth) in an oscillating universe, and thus provide a natural mechanism for anthropic selection, how we come to find ourselves in a universe that is fit for life.
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.
Perhaps inspired by the work of Hawking and Frolov, philosopher Quentin Smith published a paper (Smith 1990; commentary by Stenger 1999) proposing that random symmetry-breaking events in the initial Big Bang singularity might lead to the production of new universes via black hole singularities, and that extrapolating this process to past universes could provide a naturalistic explanation for the basic laws and constants of our universe.
In 1992 Smolin (independently of Smith) described essentially the same process in more rigorous terms, in the first peer-reviewed hard sciences paper on CNS (Did the Universe Evolve? Classical and Quantum Gravity 9:173-191). Apparently Smolin also discussed CNS for a number of years prior, perhaps even in print, as this hypothesis inspired the science fiction literature of Brin (1991).
Criticism and Current Research
While early oscillation models did not survive criticism, a number of theorists continue to work on more complex and in some cases, more biologically-inspired versions. Examples include cyclic models in brane cosmology (Steinhardt and Turok, 2001; Lehners, Steinhardt, and Turok 2009 and Baum and Frampton 2007), and the cosmological natural selection hypothesis (Smolin 1992,2006). These models remain controversial. Brane cyclic models presently offer no satisfactory description of the bounce via string theory. Likewise, the CNS description of the bounce via loop quantum gravity also remains tentative, and CNS as a framework remains difficult to evaluate without fitness function models.
Since the late 1990's we have had empirical evidence (observation of distant supernovae as standard candles, and the mapping of the cosmic microwave background) that universal expansion is not slowing but is in fact accelerating via dark energy dynamics. In most dark energy models, a future Big Crunch seems very unlikely. Nevertheless, many such models do allow for a multitude of gravitationally-driven "Small Crunches" in an accelerating universe. For example, Nagamine and Loeb (2003) project that our universe must self-fractionate into a number of informational 'islands,' or supergalaxies, each of which undergoes gravitational collapse, while the space between supergalaxies rapidly grows. Over time, the stellar black holes in each galaxy merge with the supermassive black holes at the center of each galaxy, and all matter in each supergalaxy eventually becomes entrapped inside black holes. Our local supergalaxy will comprise the collided Milky Way and Andromeda galaxies and several dwarf galaxies, and our Milky Way and Andromeda begin to collide in just 20 billion years.
When we combine CNS with dark energy models, rather than an oscillating universe which returns all its evolutionary species to a single replication point, our universe appears to be generating a diverse set of continually branching replications, just as we observe in any evolutionary developmental history of living systems exploring a phenospace. Such a continually branching replicative pattern (phylogenetic tree) is also seen in many nonliving replicating systems, such as stars replicating across a developing galaxy. Branching universe ensembles may be a way to maximize diversity, resilience, and adaptiveness, over an alternative "all eggs in one basket" Big Crunch. Questions such as these remain to be elicideated in some future information theory of replicative evolutionary developmental systems, which may have similarities whether they be chemical, biological, cultural, technological, or universal systems.
CNS with Intelligence (CNS-I)
CNS with intelligence (CNS-I) are models which attempt to bring intelligence and presumably, information theory, into the CNS framework. They propose that accumulated end-of-universe, or more precisely, end-of-black-hole evolutionary intelligence may somehow aid in universe/black hole replication and selection within the multiverse. These models assume that any universe where emergent intelligence was able to play a less-than-random role in replication or selection might become replicatively favored, more resilient, or perhaps dominant in some multiversal environment, over lineages where emergent intrauniversal intelligence does not increasingly factor into replication, as in Smolin's original CNS model.
Some CNS-I models propose that increasingly internally intelligent universes might naturally grow out of simple CNS universes at the leading edge of universal complexity, just as we have seen intelligence emerge within environmentally dominant lineages in life's history on Earth. In the most functionally and morphologically complex species on Earth, we may observe that life's intelligence mechanisms have progressed from "random" recombination of prebiotic or prokaryotic genetic elements, to a much more culturally-guided replication in higher eukaryotes. In this process, we see that individual and collective intelligence (memes, knowledge, self-awareness) increasingly influences and constrains the original and persistent "random" replicators (genes, DNA).
CNS-I models are thus consistent not only with weak observer-selection anthropic models, where our universal parameters are presumed to be anthropic (intelligence-favoring) primarily because we are here to observe them, but also with strong anthropic arguments such as the fine-tuned universe problem, where we postulate that several of our universal parameters appear improbably fine-tuned for the purpose of the emergence of life, complexity and intelligence. In other words, in CNS-I, not only universe replication and selection but also universal evolutionary developmental intelligence emergence may be considered intrinsic to the developmental telos (purpose, drive, life cycle goal) of the universe, again as long as that intelligence has a less-than-random role to play in universe selection and replication. While today's science lacks a sufficiently advanced information theory to describe the functional role of intelligence in biological evolutionary development, CNS-I models are at least suggestive of the outlines of a such an information theory, and thus worthy of research and critique.
Possibly the first written discussion of CNS-I came, appropriately enough, in science fiction. As Cyril Stanley Smith reminds us (see "The Growth of Anything Whatever," In: Search for Structure, 1981) art and play usually get to innovation first, and science fiction is a modern form of both. Responding to Smolin's prepublished work on CNS, science fiction author David Brin (1991), referring to both intrauniversal (supernovae) and extrauniversal processes of black hole replication, wrote:
- "While triggering one kind of birth, by collapsing inward, supernovas also seed through space the elements needed to make planets, and beings like me. ...I wonder if somehow that's not selected for, as well. Perhaps it is how universes evolve self-awareness."
Louis Crane's Meduso-anthropic principle (1994) also proposed, in an arxiv.org preprint, that we need to consider a role for intelligence in the CNS replication process, and provided a clear biological framework (meduesid evolution and development) to consider this prospect.
Cosmologist Edward Harrison (1995), in what was apparently the first CNS-I hypothesis to be published in a peer-reviewed journal, independently proposed that the purpose of intelligent life is to produce successor universes, in a process driven by natural selection at the universal scale.
James N. Gardner (2000,2003,2007) has also explored CNS-I ideas at length in his selfish biocosm hypothesis. After Dawkins (1976) approach to evolutionary biology, Gardner envisions self-preserving and self-selecting universal replication mechanics, which eventually lead to advanced ancestor intelligences as architects of our fine-tuned universe.
John M. Smart (2000,2008) approaches CNS-I via an evolutionary and developmental (evo devo) universe hypothesis. After Lloyd (2000), he proposes a constrained developmental destiny for higher universal intelligence in the form of black hole computational entities, in his developmental singularity hypothesis. In contrast to Gardner's universal 'architects', Smart envisions only a very limited capacity for end-of-universe evolutionary intelligence to alter universal developmental ('seed') parameters in each replication cycle, in the same way that evolutionary process alters developmental genetics only imperceptibly in each replication in biological systems. Our multiversal environment, by contrast, might be modified by ancestor intelligences to a significantly greater extent, via niche construction, again as is seen in higher biological organisms (Odling-Smee 2003).
Clément Vidal (2008, 2009a), also takes an evolutionary and developmental approach to CNS-I. He proposes that an intervention of intelligence in the universal reproduction process should be 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. More precisely, the blueprint would be fine-tuned by extensive computer simulations.
Rüdiger Vaas (2009, 2010) examined critically this extension of CNS, and pointed out far-reaching problems. A response to some of these critics can be found in Vidal (2009b).
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