Black holes in cosmological natural selection

Smolin replies: Paul Sorensen proposes an application of cosmological natural selection (CNS) according to which intelligent beings would be motivated to create artificial black holes, which would tune the ensemble of universes to favor those that are hospitable to intelligent life. Versions of that idea were proposed by Louis Crane and Edward Harrison, although Sorensen’s version is different in proposing that it could explain why the universe’s laws are comprehensible to us. His idea is elegant, but let’s wait till the few predictions of CNS are thoroughly tested and confirmed, all the objections have been answered, and alternative explanations for the selection of the laws have been disconfirmed before engaging in speculation about implications that will be hard to test.

Meanwhile, Jeffery Winkler proposes two ways that the parameters of the laws of nature could be varied to increase the number of black holes in the universe. Both are addressed in the appendix of my book The Life of the Cosmos (Oxford University Press, 1997) and related papers.

Winkler suggests that Newton’s constant, G, could be increased, which would lead to matter collapsing directly into black holes, without having to go through the stages of massive stars and supernovae. However, CNS only predicts that our universe is a local maximum of the number of black holes produced. Also, G is a dimensional constant, so what we can vary is the dimensionless ratio m, the nucleon mass in Planck units. A small increase in m will not increase the spontaneous collapse of matter to black holes. That process, so far as we know, never happens in our universe, because to overcome the Fermi degeneracy pressure requires a very large number, N ~ 1/m³ ~ 10⁵⁷, of nucleons together in a very small volume. Slightly increasing m will decrease N, but not by enough to drive spontaneous collapse. Moreover, copious black hole formation via stellar collapse requires the cooling of giant molecular clouds, which, in turn, requires plentiful carbon and oxygen, since the main coolant is carbon monoxide. But it’s not possible to have sufficient quantities of both elements without delicately tuned coincidences among the physical constants, which are disrupted when m is varied. Thus a world with a slightly larger m may have many fewer stellar-made black holes without any increase in the number of black holes formed by spontaneous collapse.

Winkler’s second proposal is to increase the baryon fraction of the universe. But that comes at a cost: Infla- tion constrains the total energy-density content of the universe. Increasing the baryon content at the expense of dark matter could result in less galaxy formation and, hence, fewer black holes. Decreasing the dark energy gives more time for galaxies to collide before the accelerating expansion disrupts clusters. And that process turns spiral galaxies with cold disks into hot ellipticals that don’t form massive stars—again resulting in fewer black holes.

Winkler further proposes that virtual black holes vastly outnumber real ones, but there is no reason based in a real calculation to suppose that virtual black holes exist or that they must spawn new universes.