▁moves ▁locally ▁at ▁c , ▁its ▁time ▁in ▁trans it ▁( about ▁ 1 3 ▁billion ▁years ) ▁is ▁not ▁related ▁to ▁the ▁distance ▁tra ve led ▁in ▁any ▁simple ▁way ▁since ▁the ▁universe ▁exp ands ▁as ▁the ▁light ▁beam ▁travers es ▁space ▁and ▁time . ▁In ▁fact ▁the ▁distance ▁tra ve led ▁is ▁inher ently ▁ambigu ous ▁because ▁of ▁the ▁changing ▁scale ▁of ▁the ▁universe . ▁Nevertheless , ▁we ▁can ▁single ▁out ▁two ▁distances ▁which ▁appear ▁to ▁be ▁phys ically ▁meaning ful : ▁the ▁distance ▁between ▁the ▁Earth ▁and ▁the ▁qu as ar ▁when ▁the ▁light ▁was ▁em itted , ▁and ▁the ▁distance ▁between ▁them ▁in ▁the ▁present ▁era ▁( t aking ▁a ▁slice ▁of ▁the ▁cone ▁along ▁the ▁dimension ▁that ▁we ' ve ▁declared ▁to ▁be ▁the ▁spatial ▁dimension ). ▁The ▁former ▁distance ▁is ▁about ▁ 4 ▁billion ▁light ▁years , ▁much ▁smaller ▁than ▁c t ▁because ▁the ▁universe ▁expanded ▁as ▁the ▁light ▁tra ve led ▁the ▁distance , ▁the ▁light ▁had ▁to ▁" run ▁against ▁the ▁t read mill " ▁and ▁therefore ▁went ▁farther ▁than ▁the ▁initial ▁separation ▁between ▁the ▁Earth ▁and ▁the ▁qu as ar . ▁The ▁latter ▁distance ▁( sh own ▁by ▁the ▁orange ▁line ) ▁is ▁about ▁ 2 8 ▁billion ▁light ▁years , ▁much ▁larger ▁than ▁c t . ▁If ▁expansion ▁could ▁be ▁instant ane ously ▁stopped ▁today , ▁it ▁would ▁take ▁ 2 8 ▁billion ▁years ▁for ▁light ▁to ▁travel ▁between ▁the ▁Earth ▁and ▁the ▁qu as ar ▁while ▁if ▁the ▁expansion ▁had ▁stopped ▁at