▁expansion ▁of ▁distance ▁by ▁a ▁factor ▁of ▁at ▁least ▁ 1 0 2 6 ▁in ▁each ▁of ▁the ▁three ▁dimensions ), ▁equivalent ▁to ▁expand ing ▁an ▁object ▁ 1 ▁nan ometer ▁( 1 0 − 9 ▁m , ▁about ▁half ▁the ▁width ▁of ▁a ▁mole c ule ▁of ▁DNA ) ▁in ▁length ▁to ▁one ▁approximately ▁ 1 0 . 6 ▁light ▁years ▁( about ▁ 1 0 1 7 ▁m ▁or ▁ 6 2 ▁tr ill ion ▁miles ) ▁long . ▁A ▁much ▁slower ▁and ▁grad ual ▁expansion ▁of ▁space ▁continued ▁after ▁this , ▁until ▁at ▁around ▁ 9 . 8 ▁billion ▁years ▁after ▁the ▁Big ▁Bang ▁( 4 ▁billion ▁years ▁ago ) ▁it ▁began ▁to ▁gradually ▁expand ▁more ▁quickly , ▁and ▁is ▁still ▁doing ▁so . ▁ ▁The ▁metric ▁expansion ▁of ▁space ▁is ▁of ▁a ▁kind ▁completely ▁different ▁from ▁the ▁exp ans ions ▁and ▁explos ions ▁seen ▁in ▁daily ▁life . ▁It ▁also ▁seems ▁to ▁be ▁a ▁property ▁of ▁the ▁universe ▁as ▁a ▁whole ▁rather ▁than ▁a ▁phenomen on ▁that ▁applies ▁just ▁to ▁one ▁part ▁of ▁the ▁universe ▁or ▁can ▁be ▁observed ▁from ▁" out side " ▁of ▁it . ▁ ▁Met ric ▁expansion ▁is ▁a ▁key ▁feature ▁of ▁Big ▁Bang ▁cosm ology , ▁is ▁mode led ▁mathemat ically ▁with ▁the ▁Fried mann - L ema ître - Ro bert son - W alk er ▁metric ▁and ▁is ▁a ▁generic ▁property ▁of ▁the ▁universe ▁we ▁inhab it . ▁However , ▁the ▁model ▁is ▁valid ▁only ▁on ▁large ▁scales ▁( rough ly ▁the