In 1973, during a symposium to celebrate the 500th birthday of Copernicus, Brandon Carter, a post-doctoral researcher in astrophysics at the University of Cambridge, tweaked his audience by stating that humanity did indeed hold a special place in the Universe - the exact opposite of what scientists from Copernicus on have said.

Since then, it has gone in and out of fashion, and the Anthropic Principle, as it was called, was most recently embraced in some M-Theory flavors of string theory.

Why? It may be science, it may be a misuse of statistics. A misuse of statistics is to say, for example, that the odds of recreating life as we know it starting from scratch is X²⁵⁰⁰⁰ to 1 or something else suitably cosmic and impossible. In reality, the odds are 100 percent. Because it happened. So it goes with physics. Some believe that because certain constants in fundamental physics seem fine-tuned to allow for the emergence of a life-enabling universe,  an Anthropic Principle guided the physics and evolution of the universe.


Copernicus, believed to be a self-portrait.

For example, it could be that constants that crisscross the Standard Model of Particle Physics guided the formation of hydrogen nuclei during the Big Bang, along with the carbon and oxygen atoms initially fused at the center of massive first-generation stars that exploded as supernovae; these processes in turn set the stage for solar systems and planets capable of supporting carbon-based life dependent on water and oxygen.

Or it could be that that is just the way it is and life might otherwise be completely different. It is speculation outside computer models, math and the outer limits of theoretical thinking.

German scholar Ulf-G Meißner, chair in theoretical nuclear physics at the Helmholtz Institute, University of Bonn, supports this Anthropic Principle in a new paper titled "Anthropic considerations in nuclear physics" and published in the Chinese journal Science Bulletin. He even says it is empirical: "One can indeed perform physics tests of this rather abstract [AP] statement for specific processes like element generation. This can be done with the help of high performance computers that allow us to simulate worlds in which the fundamental parameters underlying nuclear physics take values different from the ones in Nature.

"Specific physics problems we want to address, namely how sensitive the generation of the light elements in the Big Bang is to changes in the light quark mass m_q and also, how robust the resonance condition in the triple alpha process, i.e. the closeness of the so-called Hoyle state to the energy of 4He+8Be, is under variations in m_q and the electromagnetic fine structure constant α_{EM}." 

Brandon Carter initially posited "The universe (and hence the fundamental parameters on which it depends) must be such as to admit the creation of observers within it at some stage."

Stephen Hawking, the world's best known living physicist, has validated it, to proponents. In "A Brief History of Time," he outlines an array of astrophysics phenomena and constants that they say support the AP theory, and asks: "Why did the universe start out with so nearly the critical rate of expansion that separates models that recollapse from those that go on expanding forever, that even now, ten thousand million years later, it is still expanding at nearly the critical rate?"

"If the rate of expansion one second after the Big Bang had been smaller by even one part in a hundred thousand million million," he explains, "the universe would have recollapsed before it ever reached its present size."

Professor Ulf-G Meißner believes, "The Universe we live in is characterized by certain parameters that take specific values that appear to be remarkably fine-tuned to make life, including on Earth, possible. For example, the age of the Universe must be large enough to allow for the formation of galaxies, stars and planets, and for second- and third-generation stars that incorporated the carbon and oxygen propagated by earlier exploding stars.

"On more microscopic scales, certain fundamental parameters of the Standard Model of light quark masses or the electromagnetic fine structure constant must take values that allow for the formation of neutrons, protons and atomic nuclei." 

And while the Big Bang Nucleosynthesis gave rise to hydrogen nuclei and alpha particles (4He nuclei), elements widely regarded as essential to life including carbon and oxygen were only produced later, inside massive stars that burned bright and died quickly, some through a supernova explosion that spread these elements to later generations of star systems.

In computer simulations on JUQUUEN at Forschungszentrum Jülich, Professor Meißner and his colleagues altered the values of light quark masses from those found in Nature to determine how great a variation would prevent the formation of carbon or oxygen inside massive stars. "Variations in the light quark masses of up to 2-3 percent are unlikely to be catastrophic to the formation of life-essential carbon and oxygen," he concludes.

And earlier, during the Big Bang's generation of the nuclei of first two elements in the Periodic Table, he notes, "From the observed element abundances and the fact that the free neutron decays in about 882 seconds and the surviving neutrons are mostly captured in 4He, one finds a stringent bound on the light quark mass variations ... under the reasonable assumption that the masses of all quarks and leptons appearing in neutron β-decay scale with the Higgs vacuum expectation value."

"Thus," Professor Meißner states, "the Big Bang Nucleosynthesis sets indeed very tight limits on the variations of the light quark mass.Such extreme fine-tuning supports the anthropic view of our Universe. Clearly, one can think of many universes, the multiverse, in which various fundamental parameters take different values leading to environments very different from ours." 

Hawking stated that even slight alterations in the life-enabling constants of fundamental physics in this hypothesized multiverse could "give rise to universes that, although they might be very beautiful, would contain no one able to wonder at that beauty." 

Professor Meißner agrees with such quote-mining. "In that sense," he says, "our Universe has a preferred status, and this is the basis of the so-called Anthropic Principle."

Your move, Copernicus.

Citation:  Meißner, U. "Anthropic considerations in nuclear physics" Science Bulletin, 2015, 60(1) : 43-54 . The work received funding from DFG and NSFC (Sino-German CRC 110), Helmholtz Association (contract VH-VI-417), BMBF (grant 05P12PDFTE), the EU (HadronPhysics3 project), and from LENPIC (DEC-2103/10/M/ST2/00420). Computational resources were provided by the Jülich Supercomputing Centre (JSC) at the Forschungszentrum Jülich and by RWTH Aachen.