2019年USAAAO决赛第1题

英文题目

1. (7 points) Assuming that the present density of baryonic matter is ρb0 = 4.17*10^28 kg/m3 , what was the density of baryonic matter at the time of Big Bang nucelosynthesis (when T = 10^10 K)? Assume the present temperature, T0 to be 2.7 K.