In CCC11 we have argued that if the photon:baryon were less than ~10^6 then structure formation would be prevented because the universe would be permanently opaque and hence small density fluctuations would be supported against gravitational collapse by radiation pressure. We shall also argue in CCC12, following Tegmark and Rees (1997), that the magnitude of the primordial density fluctuations, Q, is anthropically constrained to be within an order of magnitude of its value in this universe. Despite this, Aguirre (2001) has presented the case for a universe capable of supporting life in which the photon:baryon ratio is of order unity, and Q is smaller than in this universe by a factor of between 10^-6 and 10^-3.
Aguirre argues that such a cosmology can produce stars and galaxies comparable in size, and hence longevity, to our own. As a bonus, a rich chemistry, including carbon, oxygen and nitrogen, can arise within seconds of the Big Bang.
The morale of Aguirre's work is similar to that of the weakless universe of Harnik, Kribs and Perez. By varying more than one universal constant at once, and by being bold enough to vary them by many orders of magnitude, it is possible to discover distant regions of parameter space which appear to be anthropically allowed. The key is varying more than one parameter at once, the change in one parameter effectively offsetting the change in the other. In addition, by making very large changes, the nature of the physics involved changes qualitatively.
Aguirre’s conclusion is that the existence of such a counter-example greatly reduces the explanatory power of anthropic arguments. In other words, many different sets of values of the universal constants may be consistent with the formation of life, even if they are changed by many orders of magnitude. Hence, rather than a demonstration of fine-tuning, Aguirre's case is that the fine tuning disappears so long as we allow more than one parameter to change at once.
