Cosmological natural selection

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Cosmological natural selection is a highly speculative hypothesis proposed by Lee Smolin intended as a scientific alternative to the anthropic principle. It addresses the problem of complexity in our universe, which is largely unexplained. Just a few minor changes in the mass of certain elementary particles or in the strength of the forces of the universe would prevent atoms from forming, let alone galaxies. Since natural selection has explained the complexity of life so well in biology, this concept is borrowed and applied to cosmology in an attempt to explain the complexity of the universe. Cosmological natural selection is also referred to as the theory of Fecund universes.

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[edit] The Problem of Undetermined Parameters

The standard model of elementary particle physics aims to unify the forces of nature so that they all possess the properties of a gauge field. This gauge field can be broken down naturally when combined with matter fields. In this way, we see that all the forces of nature are in fact the same force and so it only takes a small list of parameters to define all the forces in the universe (other than gravity). The matter fields have split these forces into those which we witness in our universe. However, while all forces (other than gravity) have their origin in the gauge field, there is no known origin for the matter fields that exist in our universe. The masses of the particles in our universe seem to be arbitrary in nature, not determined by any known mechanism.

If these values are in fact arbitrary, why then do they just so happen to possess just the right values to create a universe so complex? A one percent change in the mass of the neutron or proton, or a doubling of the electron's incredibly small mass, would yield a universe with no chemistry and no stars. Hydrogen gas would be the only element in the universe.

[edit] A Multitude of Universes

Virtually all hypotheses which attempt to explain this complexity involve the postulate that there is a very large or infinite number of universes, each one with its own set of mass fields. When applied to this assumption, the anthropic principle concludes that our universe is a rare exception within this large set of universes and that by chance it possesses exactly those characteristics necessary for life to exist. Since the number of universes is so large, it is expected that some of them will contain complexity. The problem with this explanation is that it is not falsifiable and is therefore unscientific in nature. That is, we know of no mechanism by which we can detect the existence of other universes (as of yet).

Modern scientific theory, however, does provide a mechanism by which universes can be formed. The original theory of general relativity predicted that when a black hole was formed it collapsed into a singularity. That is, space and time would become so curved here that everything would collapse in to a point. General relativity also predicted that our universe sprang from a singularity during the big bang. But we now know that general relativity breaks down on such small scales as the atom. It is here that quantum mechanics begins to play a part. Uncertainty reigns on these scales. For this reason, physicists have suspected for a long time that the singularity does not exist, because it would be too certain. Recently, this conjecture has been investigated mathematically. This is still speculative, but according to the theory of quantum gravity a singularity is not formed. Instead, space and time do not collapse to a point but rather into a (four-dimensional) tube which opens into an entirely new region of space and time. The singularity "bounces" back out into a big bang. This means it is entirely possible that our own universe was created when a black hole was formed in another universe.

[edit] Evolving Universes

Lee Smolin's hypothesis of cosmological natural selection makes the assumption that each universe created in such a way possesses slightly modified versions of the mass fields of its "parent" universe. This concept is of course borrowed from Darwin, and is analogous to mutation of genes in modern evolutionary theory. There is some conjectural support for this in both string theory and quantum gravity. The change in the mass fields would be due to the intense energies and small scales reached within a black hole. By a simple extrapolation it is easy to see that universes which generate more "offspring" will ultimately become more numerous. A universe with no stars and consisting entirely of hydrogen gas can produce only one offspring because it can produce no black holes. All it can do is collapse back in on itself in a "big crunch", a reverse big bang, to generate a singularity. Given enough universes, some would by chance possess the matter fields necessary to generate stars and thus black holes. Since these would produce far more offspring, they would become far more numerous than universes without stars. (There is no known mechanism that "kills off" universes and so there is no actual parallel to "natural selection" in the theory of cosmological natural selection. It is for this reason that it is now technically referred to as fecund universes.)

What Lee Smolin proposes is that a universe which produces more black holes than any other would in fact possess the laws of physics our universe does. He argues that cosmological natural selection is superior to the anthropic principle because it is falsifiable. That is, if we discover anything in our universe suggesting our universe is not ideal for producing black holes, the theory is disproven. The falsifiability in this case depends strongly on a principle of mediocrity, however. Even if universes amenable to black hole creation spawn far more universes than those that are not, there is still an anthropic landscape of possibilities. If there is an alignment of the parameters necessary for intelligent life and for black hole formation, then the fact of our existence has little effect on the prior probability part of a Bayesian calculation, but we can never neglect the possibility that we may live in a universe far from the peak of the distribution of parameters. At best, then, the principle of mediocrity provides probabilistic falsifiability. The scientific validity of such reasoning is the subject of much philosophical debate.

In addition, a thorough calculation of what exact values of the mass fields would generate a universe with the largest possible number of black holes may lead to predictions of so far unobserved elementary particles or other attributes of our universe. Unfortunately, this is not possible today.

[edit] See also

[edit] External links

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