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Ch.01 Before the UniverseCosmological Selection

Universes evolve by natural selection. Ours descends from ancestors good at making black holes.

Smolin's Cosmological Natural Selection

1992Lee SmolinSpeculativeAlso answers, Ch.02 The Origin of Our UniverseAlso answers, Ch.06 Black Holes4 primary sources, 3 established Reviewed May 14, 2026

Universes evolve by natural selection. Black holes are reproductive events, and our universe is descended from ancestors that were good at making black holes.

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§1 · The claim, in one sentence

Smolin proposed in 1992 that black holes give birth to new universes with mutated physical constants, producing a Darwinian process where our universe is fine-tuned not for life but for black hole production.

§2 · Why it might be true

Lee Smolin's idea takes the seriously but introduces a selection mechanism. He proposes that every black hole that forms in a universe produces a new universe inside it, with slightly different physical constants (the strengths of the four forces, the masses of particles, the ). The child universe expands away from the and evolves on its own.

If physical constants are inherited with small random variations, then a Darwinian process emerges. Universes that produce more black holes have more offspring. Over many generations, the population of universes becomes dominated by configurations that maximize black hole production. We are inside one of these dominant lineages.

Crucially, this is a falsifiable theory. If our universe's physical constants were perturbed slightly, the rate of black hole formation would either increase or decrease. Smolin argues that our universe sits at a near-optimal point: most small perturbations would reduce black hole production. This is the 'fine-tuning for black holes' prediction, and it's been the subject of ongoing debate.

Smolin's proposal is unusual among multiverse theories because it offers a non-anthropic explanation for fine-tuning. We're not here because we're observers; we're here because our universe is good at making the kind of objects (black holes) that propagate themselves.

The family stance

A parent universe with slightly different physical constants existed before ours. Our universe was born inside a black hole that formed in that parent universe. The same process is happening inside our black holes right now, spawning further universes with their own variations.

§2.5 · Evidence

  • The theory makes predictions that are falsifiable in principle, unlike most multiverse proposals, though critics dispute whether they can be tested in practice (see objections)
  • Some of the predicted optimizations of physical constants appear consistent with observations
  • Provides a non-anthropic explanation for the apparent fine-tuning of physical constants
  • Croon & Pinckney (2024) extend the theory by showing that dark matter (hypothetical particles thought to fill space) can seed the collapse of white dwarfs (dense burnt-out stars roughly Earth-sized) into small black holes around a tenth the mass of the Sun, a new channel for making black holes that makes the reproduction mechanism more robust.

§3 · What you'd need to test it

  • Our universe is near-optimal for black hole formation
  • Small changes to any physical constant should reduce the number of black holes formed
  • The mass distribution of stars in our universe is biased toward producing more black holes than a random distribution would
  • Neutron stars should have a maximum mass near two solar masses, since a higher ceiling would let more of them collapse into black holes and change the predicted optimum

§4 · Where it breaks

  • The "inheritance" mechanism (child universe inherits parent constants with mutation) is speculative and lacks derivation from fundamental physics
  • Different choices of "selection criterion" give different answers; black hole production is one possible criterion among many
  • Some specific predictions (e.g. about neutron star masses) have been contested by observation
  • Critics argue the theory is unfalsifiable in practice because we can't observe other universes
Go deeper

Smolin developed the proposal in his 1997 book 'The Life of the Cosmos' and in several technical papers. The key mechanism is that singularities inside black holes give rise to new expanding regions of (an idea going back to Pathria-Good and to John Wheeler's earlier speculation), and that quantum gravitational effects at the singularity could produce small random perturbations to physical constants.

The fine-tuning argument runs roughly as follows: the masses of fundamental particles and the strengths of forces determine which atomic nuclei are stable, which stars can form, and what their final masses are. Black hole formation requires sufficiently massive stars and sufficiently low metallicity in their progenitor gas clouds. Smolin argues that the observed values of physical constants are near a local maximum for black hole production rate.

Critics including Lawrence Krauss and Vilenkin have argued that the theory requires unobserved mechanisms (the inheritance process) and that its predictions about neutron star masses do not match observation. The debate continues; Smolin has updated the theory in response to specific objections.

Croon & Pinckney (2024) also show that CNS with this mechanism addresses the Boltzmann-brain problem on 10^14-year timescales, a long-standing objection to selection-based cosmologies.

▸§5 · Who built it, and when(4 sources, 3 established, 1 needs verification)
  1. Established
    Smolin (1992). 'Did the Universe Evolve?' Class. Quantum Grav. 9, 173
  2. Established
    Smolin (1997). 'The Life of the Cosmos.' Oxford University Press
  3. Established
    Smolin (2006). 'The Status of cosmological natural selection.' arXiv:hep-th/061218525 citations
  4. Needs verification
    Bramante & Raj (2024). 'Cosmology of self-replicating universes in black holes formed by dark matter-seeded stellar collapse.' Phys. Rev. D 110, 0435377 citations

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