A. it is believed that various constituents of the universe (radiation, matter and cosmological constant) provided the dominant contribution to the energy density at different times over cosmic history. in this part of the question, which considers this issue, r(t) is the scale factor at cosmic time t, and to is the present time. you can assume that the age of the universe is 13.7 billion years. also, assume th be the time at which the universe changed from being radiation-dominated to matter-dominated. i. u estimate r(t1) r(to). ii. given that the current temperature of the background radiation is 2.73 k, calculate the temperature of the radiation at t1. ili. calculate t1 using a relationship between cosmic time and temperature for the early universe and your answer from part (a)(ii). express your answer in years