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Components of Stars Prove the Delicacy of Life
By Lee Siegel
Science Writer
posted: 02:54 pm ET
06 July 2000
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By Lee Siegel If physical forces within stars were only a little different, our universe would be almost devoid of carbon and oxygen, so life would not exist, physicists have concluded in a new study."I am not a religious person, but I could say this universe is designed very well for the existence of life," said Heinz Oberhummer, a nuclear astrophysicist at the University of Vienna, Austria. 
Red-giant stars are the bright reddish-orange objects in this picture of globular star cluster M 10. The study, published in the July 7 issue of the journal Science, began five years ago when Oberhummer "was just thinking what would happen if the forces were a little different in our universe. We found that with a small change, life would not exist in the universe." He added: "Life is like a silk thread which can be torn very easily." Oberhummer and colleagues used computers to simulate or model the "triple-alpha process" by which helium burns to produce carbon during the red-giant stage of a stars life. Oxygen, a key component of life-sustaining water, is produced by the addition of a fourth alpha particle, which is a helium nucleus.The researchers varied the strengths of the "strong" force that holds protons and neutrons together in atomic nuclei, and the weaker Coulomb force that makes protons try to repel each other. They found that a change in more than one-half percent of the strong force or more than 4 percent in the Coulomb force would destroy nearly all the carbon or oxygen in every star. Under such conditions, "the creation of carbon-based life in our universe would be strongly disfavored," wrote Oberhummer and his coauthors, nuclear physicist Attila Csoto of Eotvos University in Budapest, Hungary and astrophysicist Helmut Schlattl of the Max Planck Institute for Astrophysics in Garching, Germany. ~ 
A giant red star Physicist Steven Weinberg, of the University of Texas at Austin, said he disagreed with the findings because "there are aspects of their calculations I dont find plausible. Its the nuclear physics." He said he lacked time to elaborate, but added: "If Im right, it undercuts the conclusion" about the uniqueness of conditions that spawned life. However, astrophysicist Craig Hogan, astronomy chairman at the University of Washington in Seattle, defended Oberhummer and colleagues as "good people" and said their results "should be taken seriously." Oberhummer said the findings mean "the basic forces in the universe are tailor-made for the production of carbon and oxygen, and therefore carbon-based life. At present we have no idea why the strength of the forces are fine-tuned in our universe in such a way that enables the existence of life. The fine-tuning is really very subtle." 
Helium is burned to produce carbon in the "triple-alpha process" in red-giant stars. Hogan saw no need to invoke religion or any sort of intentional design in forming the universe. "Look at modern cosmology, what we know about the Big Bang," he said. "One of the remarkable things that is quite plausible now is the idea there are many universes, and in each one of those universes the forces might be different."Missing key under the lamppost In universes where physical forces are not conducive to life, no one exists to measure those forces. But where the forces are just right to help foster life in our universe we are here to measure those forces and declare them unique. Hogan said it is like finding your missing key under a lamppost because that is where there is enough light to see it. He also said the findings provide "a hint about the way physics is put together." ~ 
Cutaway view of a helium-burning red giant. Unlike a number such as pi, which has a set value, the new study suggests fundamental physical forces "dont have a single number but can have many different values" in different universes, Hogan said. "Some scientists think it goes beyond the boundaries of science because you are talking about universes you cannot see. But I think you have to be more tolerant about that. It could be nature is made this way, and it is not the same as invoking supernatural forces."
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