Rick's Critique of the Cosmic Coincidences: Chapter 4

The Fine Tuned Weak Force? (1) The Primordial Hydrogen:Helium Ratio

During the first second after the Big Bang, temperatures are sufficiently high for neutrons and protons to interconvert via leptonic rections. This leads to a thermal equilibrium of neutron and proton abundances, the difference between the two depending upon their mass difference. The actual values of the universal constants leads to a 'prediction' that the hydrogen:helium ratio should be 75%:25% by mass, a ratio which is in good agreement with observations. The calculation depends upon the strength of the weak nuclear force. Different hydrogen:helium ratios would result if the weak force were of a different strength. This dependence is explicitly evaluated in this Chapter.

For sufficiently large increases or decreases in the strength of the weak force, the primordial universe would be virtually all hydrogen or virtually all helium respectively. This has lead some authors to claim that the weak force is fined tuned to produce a universe with similar amounts of hydrogen and helium. This claim is examined quantitatively in terms of its anthropic implications.

The primordial composition of the universe does not provide an anthropic upper bound to the strength of the weak force (GF), but does provide a ‘soft’ lower bound to GF. However, GF could be an order of magnitude smaller without fatally compromising the evolution of a universe very similar to our own. Possibly two orders of magnitude reduction in GF might be accommodated. The most serious objection to reducing GF by two orders of magnitude might be that the formation of the first stars could be compromised due to the reduced abundance of molecular hydrogen, essential for cooling. A value of GF smaller than 1% of its actual value would probably not result in a universe conducive to life. However, this assumes other constants and features of basic physics (e.g. the numbers and types of fundamental particles) to be unchanged. Even the modest claim that GF must exceed 1% of its actual value would appear to be unnecessary if other aspects of physics can be changed to suit. This is explained in Chapter 7, "The Weakless Universe".

The primordial hydrogen:helium ratio is concluded to require only the weakest of anthropic coincidences, classified as a one-sided, order-of-magnitude, coincidence only (Type D-single). It barely rates as a coincidence at all.

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Saturn's Ice Moon, Tethys: The pervasive white color of Tethys is thought to be created by fresh ice particles continually falling onto the moon from Saturn's diffuse E-ring, particles expelled by Saturn's moon Enceladus. Some of the unusual cratering patterns on Tethys remain less well understood, however. Close inspection of the above image of Tethys' south pole will reveal a great rift running diagonally down from the middle: Ithaca Chasma. A leading theory for the creation of this great canyon is anchored in the tremendous moon-wide surface cracking that likely occurred when Tethys' internal oceans froze. If so, Tethys may once have harbored internal oceans, possibly similar to the underground oceans some hypothesize to exist under the surface of Enceladus today. Might there be life down there? [Credit: Cassini Imaging Team,SSI,JPL,ESA,NASA]