first genetic material

The baryon asymmetry parameterThe challenges to the physics theories are then to explain how to produce this preference of matter over antimatter, and also the magnitude of this asymmetry. An important quantifier is the asymmetry parameter, This quantity relates the overall number density difference between baryons and antibaryons (nB and , respectively) and the number density of cosmic background radiation photon nγ.According to the Big Bang model, matter decoupled from the cosmic background radiation (CBR) at a temperature of roughly 3000 kelvins, corresponding to an average kinetic energy of . After the decoupling, the total number of CBR photons remains constant. Therefore due to space-time expansion, the photon density decreases. The photon density at equilibrium temperature T, per cubic kelvin and per cubic centimeter, is given by with kB as the Boltzmann constant,as the Planck constant divided by 2π and c as the speed of light in vacuum. In the numeric approximation at the right hand side of the equation, the convention was used (natural units), and for T in kelvins the result is given in . At the current CBR photon temperature of T = 2.725K, this corresponds to a photon density nγ of around 411 CBR photons per cubic centimeter.