Cosmological cranes – not skyhooks

In his book “Darwin’s Dangerous Idea“ Daniel Dennett draws out the philosophical significance of evolution by natural selection. Darwin himself hesitated to apply his ideas to humanity, let alone to wider philosophical issues.

Dennett describes how natural selection explains phenomena such as development and evolution, using “cranes”, rather than “skyhooks”. How development can arise internally rather than relying on an external “designer” or “manipulator.” He also describes natural selection as the “universal acid.” All this implies the concepts of natural selection can be applied more widely than just biology.

One application Dennett mentions is in cosmology and he briefly describes Lee Smolin’s idea of cosmological natural selection in his book. 2009 is the International Year of Astronomy. It is also the year we celebrate the 200^th anniversary of Darwin’s birth (February 12) and the 150^th anniversary of publication of his The Origin of Species. So it is fitting to link the two commemorations and cosmological natural selection does this.

Cosmological natural selection

I am currently reading Smolin’s book “The Life of the Cosmos“ where he presents this idea in detail. It’s a fascinating idea and explains why the physical constants have the values they do in our universe (the “fine-tuning” problem) and why they are favourable to life. It shows how we can provide a mechanism for a “multiverse” as a natural phenomenon, one in which life-favourable universes are typical rather than rare as in the common anthropic explanations of a “multiverse.” It’s also an idea which is open to testing, even at our current scientific level.

The cosmological natural selection idea rests on the proposition that black holes can act as sources of child universes. He compares the ‘singularities’ of black holes to the ‘singularity’ preceding the “big bang”. However, whereas these ‘singularities’ arise from the breakdown of relativity theory at high mass and short distances he suggests quantum-mechanical effects could prevent ‘singularities’ and instead lead to a ‘bounce.’ When we look at the “big bang” we see a past ‘bounce.’ With a black hole we see a future ‘bounce’ where rather than time disappearing it ‘goes through’ the black hole and continues into a new region of space-time – into a new universe.

Selection for black holes – and carbon

Smolin suggests the child universe inherits the values of it physical constant from the parent universe – with the possibility of random small changes in value. This sets up a mechanism for the natural selection of universes in a population – those universes which have values of physical constants favouring formation of black holes will produce more offspring. Eventually universes with such values of physical constants will be preferred and so dominate the population of possible universes.

An interesting idea coming out of cosmological natural selection is that back hole formation is favoured if stars can form, especially more massive stars. It turns out that this is influenced by the chemistry of molecular clouds in the interstellar medium. If the values of the physical constants favour formation of carbon this provides a chemistry, including carbon monoxide, which allows the radiative loss of heat from the clouds. Cooling of the molecular clouds must occur before gravitational forces can lead to condensation of stars.

So cosmological natural selection could explain formation of universes like ours with many black holes and a chemistry that includes carbon. Universes capable of supporting our sort of life.

Criticism and evaluation

Smolin has done some testing of this idea by calculating the effect changing the values of some of the physical constants would have in the predicted number of black holes in a universe. In the cases he has been able to test, changes have led to a decrease in the number of black holes – away from that arising from natural selection. This supports the idea that we could be in a typical universe that was the member of a population evolved by cosmological natural selection. Apparently recent progress in loop quantum gravity theory also support Smolin’s hypothesis.

Lee Smolin’s proposal has received less consideration from other scientists than it probably deserves. Physicist Leonard Susskind has offered his criticisms in an Edge discussion and Gordon McCabe has offered both a critique and an extension of the idea. McCabe’s papers are worth reading because they provide a clear, and fairly mathematics-free, description of cosmological natural selection.

While we have to treat this idea as speculative – I like it. Especially if we have to accept the possibility of other universes and if we cannot develop a fundamental theory providing support for the idea the values of the physical constants are “natural” – that they could not be otherwise. I like it because it uses “cranes” rather than “skyhooks.”

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