▁in ▁time ▁become ▁important . ▁ ▁These ▁situations ▁are ▁described ▁by ▁general ▁relativ ity , ▁which ▁allows ▁the ▁separation ▁between ▁two ▁distant ▁objects ▁to ▁increase ▁faster ▁than ▁the ▁speed ▁of ▁light , ▁although ▁the ▁definition ▁of ▁" separ ation " ▁is ▁different ▁from ▁that ▁used ▁in ▁an ▁in ert ial ▁frame . ▁ ▁This ▁can ▁be ▁seen ▁when ▁obser ving ▁distant ▁galaxies ▁more ▁than ▁the ▁Hub ble ▁radius ▁away ▁from ▁us ▁( appro xim ately ▁ 4 . 5   g ig ap arse cs ▁or ▁ 1 4 . 7 ▁billion ▁light - year s ); ▁these ▁galaxies ▁have ▁a ▁re cess ion ▁speed ▁that ▁is ▁faster ▁than ▁the ▁speed ▁of ▁light . ▁Light ▁that ▁is ▁em itted ▁today ▁from ▁galaxies ▁beyond ▁the ▁cosm ological ▁event ▁horizon , ▁about ▁ 5   g ig ap arse cs ▁or ▁ 1 6 ▁billion ▁light - year s , ▁will ▁never ▁reach ▁us , ▁although ▁we ▁can ▁still ▁see ▁the ▁light ▁that ▁these ▁galaxies ▁em itted ▁in ▁the ▁past . ▁Because ▁of ▁the ▁high ▁rate ▁of ▁expansion , ▁it ▁is ▁also ▁possible ▁for ▁a ▁distance ▁between ▁two ▁objects ▁to ▁be ▁greater ▁than ▁the ▁value ▁calculated ▁by ▁multip lying ▁the ▁speed ▁of ▁light ▁by ▁the ▁age ▁of ▁the ▁universe . ▁These ▁details ▁are ▁a ▁frequent ▁source ▁of ▁confusion ▁among ▁am ateurs ▁and ▁even ▁professional ▁phys ic ists . ▁Due ▁to ▁the ▁non - int uit ive ▁nature ▁of ▁the ▁subject ▁and ▁what ▁has ▁been ▁described ▁by ▁some ▁as ▁" care less " ▁choices ▁of ▁word