Cosmologists believe that the CMB we observe was emitted about 14 billion years ago at a temperature of about 3,000 ° C. However, with the expansion of the universe since that time, it has cooled to only about -270 ° C.
宇宙論學者相信，背景輻射剛被釋放出來時，溫度約為攝氏 3,000 度，但經過近 140 億年的膨脹冷卻，目前溫度已約降至攝氏零下 270 度。