Oldest light

The oldest light in the universe belongs to the Cosmic Microwave Background (CMB). When the universe was born in the Big Bang, the tremendous amount of light generated in the explosion remains in the cosmos to the present day. Now cool and stretched out by the expansion of the universe itself, the CMB is present everywhere and can be seen as photons coming from all directions. Recent observations of the CMB show that it is very uniform, but small variations in the full-sky map could yield clues to how the universe started. The current estimated age of the CMB light, and hence the universe itself, is 13.75 ± 0.13 billion years (4.336 x 1017 seconds in SI units, or 13.75 Gigayears).