Over the past week I have been reviewing some of the possible solution for the fine tuning problem of cosmology. One option is that some aspect of quantum mechanics requires the Universe to contain a sentient observer, and in effect cause the Universe to fine tune itself. Another possibility is that there are a very large number of Universes aside from our own, and with each Universe having slightly differently properties it follows that a few will be habitable. Today we will look at another very interesting possibility, that the Universe itself is actually evolving.

Since the development of the theory of general relativity over a century ago, it has been known that there exist objects in the Universe which are so massive and so dense that not even light can escape. These are known as black holes, and anything that enters a black hole is forever cut off from the rest of the Universe. In effect, the interior of a black hole is a separate Universe.

Suppose that the laws of physics or the values of some fundamental constants of nature change slightly inside a black hole. They certainly involve high energy reactions, and it is known that at very high energies some of the fundamental forces of nature can be altered. Perhaps these isolated regions of spacetime form new baby Universes in which the laws of nature are slightly different than in the parent Universe.

And that has some very interesting consequences. If a Universe can spawn several baby Universes with slightly different physical laws, then it can evolve in a way analogous to biological evolution. The fundamental constants form the genetics, and black holes are the offspring that carry on the genetics. A primordial Universe formed a few black holes, each of which had slightly different laws of physics, and each of which expanded to form a new Universe. In each of these baby Universes more black holes form, and each of those has slightly different laws of physics and each forms a new Universe, and so on ad infinitum.

The primary prediction of this model is that the fundamental constants of nature should be precisely those required to form a large number of black holes. The Universe evolves for the sole purpose of reproducing itself in the form of black hole baby Universes. So what would we expect from a Universe that is the result of countless generations of evolution?

Obviously the Universe would have to live long enough for star to form, live out their lives, and then collapse into black holes. Ideally it would live long enough for several generations of stars to form. We would also expect that nuclear physics would be tuned in such a way that heavy elements can form, because heavy elements allow for denser astrophysical objects to form. It would also be expected that electromagnetic and nuclear forces will be strong enough that matter clumps together, and yet not so strong as to prevent other reactions and astrophysical processes from occurring. Gravity would have enough strength to form black holes, but also weak enough that the Universe doesn't immediately collapse before many black holes have formed.

Surprisingly, these are the exact properties that the Universe must have to support life. It turns out that black hole formation and the development of advanced life forms require very similar laws of physics.

And so perhaps the reason that the Universe supports life is nothing more than an odd coincidence. Perhaps the Universe evolved to produce black holes, and life was just an interesting side effect. It might not make humanity seem so special, but it would certainly explain why the Universe should appear fine tuned. It may be nothing more than the result of endless eons of evolution. 

So that is the state of the fine tuning problem right now. It could be a quantum mechanical effect that requires intelligent observers, or it could be due to the existence of numerous Universes and we live in the rare one that happens to be habitable, or perhaps the Universe has evolved to support life. Or perhaps it is something else that we have not yet even thought of! For now all we can do is look at the stars and contemplate why we are here...