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3.1. Baryogenesis

The baryon to photon ratio eta is determined during baryogenesis [3], [36], [37]. It is not known when baryogenesis occurred. Sakharov [38] noted that three conditions are required: different interactions for matter and anti-matter (CP violation), interactions which change the baryon number, and departure from thermodynamic equilibrium. This last condition may be satisfied in a first order phase transition, the GUT transition at 10-35 s, or perhaps the electroweak transition at 10-11 s. If baryogenesis occurred at the electroweak scale, then future measurements may lead to predictions for eta, but if, alternatively, baryogenesis is at the GUT or inflation scale, it will be very hard to predict eta (J. Ellis personal communication).

The matter/anti-matter asymmetry of the universe (the eta value) is attracting discussion in the popular science press because of the inauguration of major experiments to study CP violation in B mesons ([41], [42]; Economist, May 8 1999, 85-87).