issue 17 :: August 2010

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SCIENCE: Lee Smolin

The Life of the Cosmos, 358pg., Oxford University Press, 1997

Physicist Lee Smolin's remarkably inventive yet cautious book seeks to explain not only why the laws of physics in our universe have the properties we observe, but also why these laws are obviously favorable to the existence of living creatures. This bold line of reasoning goes past any Theory of Everything to posit that different universes can have different sets of values defining the fundamental properties of each universe; the mass of the electron, for example. You can imagine a universe just like ours, but the mass of the electron is doubled. How would that affect that universe? If you could randomly choose among these 21 parameters, you would have a preposterously large set of possibility universes, but only a tiny faction of these would lead to anything resembling our life-filled world. Why does the universe seem tuned in to a rare set of conditions that make the universe capable of such complexity? The typical, historical efforts to explain this mystery can be broken down to a) God (“I am inclined to consider the Cosmos as a game of God.” -André Gide, Journal), b) anthropomorphic principal (it's like that because if it weren't, we wouldn't exist) and c) crackpot. And while the audacity of Smolin's idea may at first glance fall into the last category, he goes out of his way to point out where current gaps in our knowledge (a lack of a quantum theory of gravity for example) could disprove his theory. He also calls his theory speculation. Crackpots are rarely so modest or well-written.

Calling it in this book Cosmic Natural Selection (and later as the Fecund Universe Theory), Smolin starts with two assumptions: 1) inside every black hole exists not a complete singularity, but the high-energy density conditions equal to the Big Bang that created our universe, creating a new "child" universe, and 2) each new universe has similar but slightly different properties from the “parent” universe. Similar to biological evolution, a universe that generates more black holes creates more universes with similar black hole-generating properties. Eventually one would expect most universes, if you could choose to observe any at random, to have properties that would maximize the production of black holes.
For example, consider the gravitational constant g, the measure of the strength of gravity. A universe with g much smaller than ours would be too weak to make atoms or stars much less black holes and planets like the Earth; everything would fly away from everything else. Now consider a universe with a g much larger that our universe. Everything would immediately clump together into a “Big Crunch,” presumably bouncing back into another Big Bang.
Our universe has a gravitational constant that seems to generate many black holes: there is probably one in the center of every galaxy and at the end of every large (3+ solar mass) star. Out of 21 constants that define our universe, Smolin claims we know enough about eight of these constants to roughly calculate how changes in these constants could effect black hole production, and like the case of the gravitational constant above, one can argue that eight of these constants seem to be in the narrow ranges necessary to allow atoms/stars/galaxies to form, etc. Smolin stresses there is much we do not yet know about these matters, and we are far from being able to say with any certainty how exactly what ranges of parameters would produce universes with less black holes. But for Smolin, being able to show that these 21 constants create a universe that maximizes black hole production is proof of Cosmic Natural Selection. There probably can be no direct observation of these other universes.
Smolin links a universe that is hospitable to black holes with a universe that can be hospitable to life, and this link is carbon, without which it would be hard to imagine the molecules that allow such complexity of life. Also, without carbon, it is hard to imagine how stellar evolution can progress to the iron-burning cores of massive stars that leads to the catastrophic supernovas that produce black holes. And the link goes further: it is the black hole generating supernovas that also spew carbon and other heavy elements forged within these massive stars into the interstellar dust clouds that form new stars and planets. Something that would prevent supernovas and black holes, would also prevent life (as we know it).
There is much more to this book and theory than can be quickly summarized here. But in a simplified overview, how are we to judge this theory? Looking at the two main assumptions: 1) lacking a quantum theory of gravity, we don't know what happens inside a black hole. Smolin admits this. 2) Smolin doesn't explain why a child universe would have similar properties to the parent universe. Why wouldn't it have the exact same properties? Or, the creation of a black hole being such a catastrophic event, why wouldn't all the constants of the child universe be different? And beyond the assumptions, what happens to the child universes when two black holes collide? Or when a black hole evaporates by Hawking radiation?
Setting aside this theory's validity, Smolin's writing is remarkably clear and free from the typical, dumbed-down analogies that plague many science books for the general reader. Whether or not you are convinced by his careful arguments, there is much to learn here about cosmology, entropy, galaxy structure, particle physics and biology, with many references to the works of others for further reading. Smolin's two other books, Three Roads to Quantum Gravity and The Trouble with Physics (concerning the history of String Theory) share this clear writing and plethora of useful references.
This month, Smolin updated his 2006 rather technical update (not for the general reader), “The status of cosmological natural selection” on the scientific preprint server arVix.
review by Josh Ronsen
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