▁developed ▁his ▁gravit ational ▁theory . ▁ ▁Com oving ▁coordinates ▁ ▁In ▁expand ing ▁space , ▁proper ▁distances ▁are ▁dynam ical ▁quantities ▁which ▁change ▁with ▁time . ▁An ▁easy ▁way ▁to ▁correct ▁for ▁this ▁is ▁to ▁use ▁com oving ▁coordinates ▁which ▁remove ▁this ▁feature ▁and ▁allow ▁for ▁a ▁character ization ▁of ▁different ▁locations ▁in ▁the ▁universe ▁without ▁having ▁to ▁character ize ▁the ▁physics ▁associated ▁with ▁metric ▁expansion . ▁In ▁com oving ▁coordinates , ▁the ▁distances ▁between ▁all ▁objects ▁are ▁fixed ▁and ▁the ▁instant aneous ▁dynamics ▁of ▁matter ▁and ▁light ▁are ▁determined ▁by ▁the ▁normal ▁physics ▁of ▁gravity ▁and ▁elect romagnet ic ▁radiation . ▁Any ▁time - e volution ▁however ▁must ▁be ▁account ed ▁for ▁by ▁taking ▁into ▁account ▁the ▁Hub ble ▁law ▁expansion ▁in ▁the ▁appropriate ▁equations ▁in ▁addition ▁to ▁any ▁other ▁effects ▁that ▁may ▁be ▁operating ▁( gravity , ▁dark ▁energy , ▁or ▁curv ature , ▁for ▁example ). ▁Cos m ological ▁simulations ▁that ▁run ▁through ▁significant ▁fra ctions ▁of ▁the ▁universe ' s ▁history ▁therefore ▁must ▁include ▁such ▁effects ▁in ▁order ▁to ▁make ▁applicable ▁predictions ▁for ▁observ ational ▁cosm ology . ▁ ▁Under standing ▁the ▁expansion ▁of ▁the ▁universe ▁ ▁Me asure ment ▁of ▁expansion ▁and ▁change ▁of ▁rate ▁of ▁expansion ▁ ▁In ▁principle , ▁the ▁expansion ▁of ▁the ▁universe ▁could ▁be ▁measured ▁by ▁taking ▁a ▁standard ▁r uler ▁and ▁meas uring ▁the ▁distance ▁between ▁two ▁cosm olog ically ▁distant ▁points , ▁waiting ▁a ▁certain ▁time , ▁and ▁then ▁meas uring ▁the ▁distance ▁again , ▁but ▁in ▁practice , ▁standard ▁r