Final answer:
The uniform temperature of the cosmic microwave background radiation is approximately 2.73 K. This remarkable uniformity suggests that all parts of the visible universe were in contact at some point and came to the same temperature.
Step-by-step explanation:
The uniform temperature of the cosmic microwave background radiation is approximately 2.73 K. This temperature was determined from measurements of the microwave radiation that permeates space and is of cosmic origin. This radiation is known as the cosmic microwave background (CMB) and it exhibits a blackbody spectrum.
The remarkable uniformity of the CMB temperature, which is the same to about 1 part in 100,000 everywhere we look, suggests that all parts of the visible universe were in contact at some point in time and had the time to come to the same temperature, similar to how ice melts and water cools down to the same temperature.