The Fine-Tuning of the Universe for Life Just Got Finer
This could be seen as a very cool addendum to Michael Denton's new article in BIO-Complexity on the fine-tuning of the biosphere, which David Klinghoffer writes about above. In Physical Review Letters, a team of physicists reports an increase of precision in one of the most important examples of fine-tuning that allow for life in the universe ("Viability of Carbon-Based Life as a Function of the Light Quark Mass").
Formed by the burning of helium in red giant stars, carbon and oxygen are two elements on which all life is predicated. The carbon-12 isotope in particular, which makes up almost all of that element as it exists in us and everywhere else you'll find it, forms only under very special circumstances, dependent on an excited state of the isotope, the "Hoyle state."
The excitation of carbon-12 is called the "Hoyle state" because Fred Hoyle precisely deduced its energy, necessary for our universe to have the carbon and oxygen it does. From the paper:
The Hoyle state plays a crucial role in the helium burning of stars that have reached the red giant stage. The close proximity of this state to the triple-alpha threshold is needed for the production of carbon, oxygen, and other elements necessary for life. We investigate whether this life-essential condition is robust or delicately ﬁne-tuned by measuring its dependence on the fundamental constants of nature, speciﬁcally the light quark mass and the strength of the electromagnetic interaction. We show that there exist strong correlations between the alpha particle binding energy and the various energies relevant to the triple-alpha process. We derive limits on the variation of these fundamental parameters from the requirement that sufﬁcient amounts of carbon and oxygen be generated in stars.Yes, the "life-essential condition" turns out to be very highly fine-tuned indeed. From the news release, quoting physicist Dean Lee at North Carolina State University:
In new lattice calculations done at the Juelich Supercomputer Centre [in Germany] the physicists found that just a slight variation in the light quark mass will change the energy of the Hoyle state, and this in turn would affect the production of carbon and oxygen in such a way that life as we know it wouldn't exist.Somewhere, Hoyle must be pleased. Talk about a sweet example of prediction and discovery.
"The Hoyle state of carbon is key," Lee says. "If the Hoyle state energy was at 479 keV [479,000 electron volts] or more above the three alpha particles [helium-4 nuclei], then the amount of carbon produced would be too low for carbon-based life.
"The same holds true for oxygen," he adds. "If the Hoyle state energy were instead within 279 keV of the three alphas, then there would be plenty of carbon. But the stars would burn their helium into carbon much earlier in their life cycle. As a consequence, the stars would not be hot enough to produce sufficient oxygen for life. In our lattice simulations, we find that more than a 2 or 3 percent change in the light quark mass would lead to problems with the abundance of either carbon or oxygen in the universe."
Image credit: "Hubble Sees Red Giant Blow a Bubble," ESA/NASA.