Rick's Critique of the Cosmic Coincidences: Chapter 5

The Fine Tuned Weak Force? (2) Type II Supernovae

Type II supernovae are the spectacular explosions which mark the death of massive, isolated stars. Their anthropic significance is that they are the means by which the heavy elements created within a star are ejected into the universe at large. The physics underlying Type II supernova explosions is not simple. This is an active area of research and there is not yet agreement on all the details, though computer simulations are becoming convincing. However, there is a consensus that the large bulk of the energy released in a supernova explosion is in the form of neutrinos, perhaps as much as 99%. It is generally believed that the transfer of a fraction of this neutrino energy to the star's mantle is essential in causing the supernova. It is amusing that the neutrinos, whose interactions in other circumstances are so weak as to be virtually non-existent, are resonsible for the most energetic explosions in the universe

The key problem in the theory of Type II supernovae is elucidation of the mechanism for transferring the neutrino energy to the mantle. Many authors have claimed that fine tuning of the strength of the weak nuclear force (GF) is required for supernovae to occur. The argument is that the interaction strength must be delicately balanced to allow the neutrinos to escape the core and yet transfer significant energy to the mantle. We attempt to examine this claim quantitatively in this Chapter. The attempt is frustrated by the inability of simple 'hand calculation' arguments to address the complex supernova phenomenon adequately.

Nevertheless, by equating the dynamical timescale with the neutrino reaction time an estimate of the Fermi constant (GF) required for supernovae to occur is obtained. Assuming a very crude estimate for the density of the active mantle, together with a neutrino energy of 40 MeV, the required Fermi constant (GF) is shown to be close to its actual value.

In conclusion, the occurrence of Type II supernovae appears to require fine tuning of the weak force classified as a Type D coincidence. It is feasible that the coincidence required is actually more fine tuned than this, e.g. Type C or even type B, but very detailed computer calculations would be required to determine if this is so.

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The International Space Station Over the Horizon (taken by the crew of the Space Shuttle Atlantis as they departed the ISS on their way back to Earth, December 2009). The ISS's crew currently includes astronauts representing NASA, the European Space Agency, the Russian Federal Space Agency, and the Canadian Space Agency. [Credit: STS-129 Crew, Expedition 21 Crew, NASA]