May 20, 2008

The Three Fundamental Forces of Nature

The building blocks of matter[hep-ph/0604027] A Universe Without Weak Interactions (Roni Harnik, Graham D. Kribs, Gilad Perez, Physical Review D, 74, 035006, 2006) is a nice piece of worldbuilding. It is also fun to hear an abstract start: "A universe without weak interactions is constructed that undergoes big-bang nucleosynthesis, matter domination, structure formation, and star formation." It is unfortunately a purely theoretical paper with no experimental predictions in principle; an experimental construction of a physical universe would make a really cool paper.

Anyway, the point is mainly to demonstrate that one can tweak the standard cosmological models to leave out all of the weak nuclear force and still get what looks like a habitable universe. This means that anthropic arguments likely cannot set fine-tuning in the weak domain: our existence doesn't imply that we have to have a weak nuclear force.

Their weakless universe just has electrons, up, down and strange quarks (with antiparticles), no neutrinos, other leptons or heavy quarks. Neutrons and the Λ0 particle are stable. A lot more isotopes are stable, especially very neutron-rich isotopes. Much of the paper deals with tweaking the initial abundances of quarks and photons to get enough hydrogen (deuterium) for stars. The heaviest naturally occuring element would be Strontium 76 (Molybdenium 84 is also stable but cannot be manufactured in normal star processes). Stars mainly burn deuterium into helium 4, catalyzed by protons. Stars are about a hundred times less massive and less luminious, but last as long as our stars. Supernovae "fizzle" because the core cannot rapidly cool by emitting neutrinos, making heavy stars end up as black holes or neutron-proton stars without blowing off their atmosphere. Accretion supernovae still work, and enrich the interstellar medium with heavy elements.

All in all, a pretty cool piece of worldbuilding. My biggest problem with it is that in the absence of slow radioactive decay inside planets they will lose plate tectonics rapidly. This would prevent the carbon-silicon cycle and make planetary atmospheres too low in carbon dioxide to maintain a greenhouse effect. This is likely not an insurmountable problem for the emergence and persistence of life, but the vast majority of terrestrial planets will likely be frozen out.

Posted by Anders3 at May 20, 2008 10:27 AM