▁the ▁earlier ▁time , ▁it ▁would ▁have ▁taken ▁only ▁ 4 ▁billion ▁years . ▁ ▁The ▁light ▁took ▁much ▁longer ▁than ▁ 4 ▁billion ▁years ▁to ▁reach ▁us ▁though ▁it ▁was ▁em itted ▁from ▁only ▁ 4 ▁billion ▁light ▁years ▁away , ▁and , ▁in ▁fact , ▁the ▁light ▁em itted ▁towards ▁the ▁Earth ▁was ▁actually ▁moving ▁away ▁from ▁the ▁Earth ▁when ▁it ▁was ▁first ▁em itted , ▁in ▁the ▁sense ▁that ▁the ▁metric ▁distance ▁to ▁the ▁Earth ▁increased ▁with ▁cosm ological ▁time ▁for ▁the ▁first ▁few ▁billion ▁years ▁of ▁its ▁travel ▁time , ▁and ▁also ▁indicating ▁that ▁the ▁expansion ▁of ▁space ▁between ▁the ▁Earth ▁and ▁the ▁qu as ar ▁at ▁the ▁early ▁time ▁was ▁faster ▁than ▁the ▁speed ▁of ▁light . ▁None ▁of ▁this ▁surprising ▁behavior ▁origin ates ▁from ▁a ▁special ▁property ▁of ▁metric ▁expansion , ▁but ▁simply ▁from ▁local ▁principles ▁of ▁special ▁relativ ity ▁integrated ▁over ▁a ▁cur ved ▁surface . ▁ ▁Top ology ▁of ▁expand ing ▁space ▁ ▁Over ▁time , ▁the ▁space ▁that ▁makes ▁up ▁the ▁universe ▁is ▁expand ing . ▁The ▁words ▁' space ' ▁and ▁' un iverse ', ▁sometimes ▁used ▁inter change ably , ▁have ▁distinct ▁mean ings ▁in ▁this ▁context . ▁Here ▁' space ' ▁is ▁a ▁mathematical ▁concept ▁that ▁stands ▁for ▁the ▁three - dimensional ▁manifold ▁into ▁which ▁our ▁respective ▁positions ▁are ▁embedded ▁while ▁' un iverse ' ▁refers ▁to ▁everything ▁that ▁exists ▁including ▁the ▁matter ▁and ▁energy ▁in ▁space , ▁the ▁extra - dim ensions ▁that ▁may ▁be ▁wrapped ▁up ▁in ▁various ▁strings