- Evidence Against Fine Tuning for Life
Don N. Page
pretty much tells you its content. Page argues that the fraction of baryons that condense gravitationally into structures large enough to allow for the development of life depends on the value of the cosmological constant in such a way that the fraction of baryons monotonically decreases for all positive values of the cosmological constant. Thus, Page concludes, the observed value of the cosmological constant is not optimal for the evolution of life - any smaller positive number would be better. He offers an estimate that in fact a small negative number would be the optimal value. Consequently, our universe is not fine-tuned for life.
Besides the relation between the cosmological constant and baryon condensation being more subtle than Page takes it to be, there are other reasons why this conclusion might not hold that Page also mentions in his discussion. It could be for example that there is an unknown constraint preventing an independent variation of the cosmological constant without also altering other constants. Or the fraction of baryons is not monotonically related to the probability of forming life. Though this relation seems plausible, it is an additional assumption.
Page's argument adds to previous studies indicating that life may be possible with other constants of nature, if several of them are changed simultaneously - a possibility that is often left out in the common arguments of the sort "if only [some constant] was a little bit smaller or larger, then [some disaster would happen]." Harnik, Kribs & Perez have for example suggested a model without weak interaction, the "weakless universe," that leaves chemistry and nuclear physics almost unchanged, such that evolution of life could still take place. (See "A Universe Without Weak Interactions," arXiv:hep-ph/0604027.)
So, is the universe fine-tuned for life? Probably not.
This might seem quite depressing for a scientist who sees his God's role becoming ever more constrained by modern research and wishes to let Him at least chose constants of Nature that are "just right" for our existence. Page however does not falter in his belief. Instead, he interprets his argument as support for the multiverse:
"It could be taken as negative evidence for theists who expect God to fine tune the constants of physics optimally for life. However, for other theists, such as myself, it may simply support the hypothesis that God might prefer a multiverse as the most elegant way to create life and the other purposes He has for His Creation."I have nothing to say to this except "Amen."