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| Cosmological natural selection | |
|---|---|
| Name | Cosmological natural selection |
| Field | Theoretical cosmology |
| Proposer | Lee Smolin |
| Introduced | 1992 |
| Related | Multiverse theory, Black hole thermodynamics, Inflationary cosmology |
Cosmological natural selection is a speculative theoretical framework proposing that physical constants and laws may be shaped by a Darwinian-like reproductive process operating across a population of universes. It posits that universes that produce more progeny via black hole formation become more numerous, leading to an anthropically favorable distribution of parameters without invoking design or teleology. The hypothesis links ideas from Lee Smolin, black hole thermodynamics, multiverse, quantum gravity, and astrophysics to explain apparent fine-tuning in particle physics and cosmology.
The proposal originated in the context of debates about the cosmological constant problem, the hierarchy between the Planck scale and the electroweak scale, and the apparent fine-tuning required for complex structures like galaxies, stars, planets, and life. It was articulated as an alternative to selection arguments associated with the anthropic principle invoked in discussions around the string theory landscape, inflationary cosmology, and proposals such as eternal inflation and the many-worlds interpretation of quantum mechanics. The idea seeks to use mechanisms familiar from biological evolution—variation, replication, and selection—transposed into a cosmological setting discussed in forums such as Physical Review D and meetings at institutions like the Perimeter Institute and CERN.
The core mechanism hypothesizes that each collapsing region forming a black hole seeds a new, causally disconnected expanding region—a daughter universe—with slightly altered values of fundamental parameters. This draws on concepts from general relativity, conjectures about black hole interiors in loop quantum gravity, and speculative bounce scenarios influenced by ideas from Roger Penrose and alternatives considered by Stephen Hawking and Kip Thorne. Variation between offspring universes could be driven by quantum processes at the Planck epoch or through mechanisms analogous to symmetry breaking in models like Grand Unified Theory and supersymmetry. Selection favors parameter sets that maximize black hole production, creating a statistical bias across the multiverse analogous to selection pressures described by Charles Darwin and formalized in population genetics by figures such as R. A. Fisher.
Smolin and others articulated several empirical predictions intended to distinguish the hypothesis from competing ideas. These include constraints on stellar evolution models relevant to supernova rates, limits on the neutron star maximum mass linked to observations by observatories like LIGO and VIRGO, and implications for the observed value of the cosmological constant measurable via surveys such as the Sloan Digital Sky Survey and missions like Planck (spacecraft). The framework predicts that small variations in constants (e.g., the fine-structure constant, proton-to-electron mass ratio) should, generically, reduce black hole formation, a claim testable through comparisons with data from Hubble Space Telescope, Chandra X-ray Observatory, and nucleosynthesis constraints from Big Bang nucleosynthesis. Other suggested tests rely on probes of high-energy physics from Large Hadron Collider results and precision cosmology from WMAP.
The hypothesis is compared with models including the string theory landscape, which invokes a vast discretuum of vacua possibly populated via eternal inflation driven by scalar fields such as the inflaton. It contrasts with approaches favoring explanatory selection via the anthropic principle articulated in debates involving figures like Steven Weinberg and Andrei Linde. Unlike many-worlds interpretation applications that emphasize branching quantum histories studied by Hugh Everett, the cosmological natural selection proposal invokes real physical reproduction mediated by gravitational collapse, a notion sometimes explored in bounce cosmology and cyclic universe scenarios associated with researchers like Paul Steinhardt and Neil Turok.
Critiques focus on the speculative nature of the reproduction mechanism, the lack of a detailed microphysical derivation from a complete theory of quantum gravity, and challenges in producing definitive falsifiable predictions. Critics include proponents of the anthropic principle and defenders of the string theory landscape such as Joseph Polchinski and Leonard Susskind, who question the statistical foundations and predictive power. Philosophers of science like Karl Popper and scientists engaged in methodological debates at venues like Nature (journal) and Science (journal) have debated whether the hypothesis meets criteria for scientific testability. Observational counterexamples from measurements of neutron star masses by teams using instruments at Arecibo Observatory and NICER have been cited as tensions, prompting refinements and alternative parameter-space analyses.
The idea was most prominently proposed by Lee Smolin in the early 1990s and developed through publications, conference presentations, and exchanges with researchers in quantum gravity and cosmology. Related antecedents and influences include discussions by John Wheeler on “space-time foam” and absorption of concepts from black hole thermodynamics by Jacob Bekenstein and Stephen Hawking. Other contributors who have engaged critically or developed variations include Alexander Vilenkin, Andrei Linde, Martin Rees, and researchers at institutions such as Institute for Advanced Study and Kavli Institute for Theoretical Physics.
If realized, the mechanism would offer an evolutionary explanation for observed parameter values, linking microphysical constants to large-scale astrophysical processes and providing an alternative pathway to addressing fine-tuning problems confronted by particle physics experiments at Fermilab and cosmological surveys like Euclid (spacecraft). It would influence priorities in searches for new physics, motivate specific astrophysical measurements, and reshape discussions about the role of selection effects in cosmological inference debated at conferences hosted by Royal Society and research programs funded by agencies such as the National Science Foundation. The proposal remains a provocative interface between empirical astrophysics, speculative quantum gravity, and philosophical questions about scientific explanation.
Category:Theoretical cosmology