▁was ▁determined ▁that ▁there ▁is ▁no ▁evidence ▁for ▁any ▁' slow ing ▁down ' ▁of ▁the ▁expansion ▁in ▁the ▁current ▁epo ch . ▁ ▁Observ ational ▁evidence ▁The oret ical ▁cosm olog ists ▁developing ▁models ▁of ▁the ▁universe ▁have ▁drawn ▁upon ▁a ▁small ▁number ▁of ▁reasonable ▁assumptions ▁in ▁their ▁work . ▁These ▁work ings ▁have ▁led ▁to ▁models ▁in ▁which ▁the ▁metric ▁expansion ▁of ▁space ▁is ▁a ▁likely ▁feature ▁of ▁the ▁universe . ▁Chief ▁among ▁the ▁underlying ▁principles ▁that ▁result ▁in ▁models ▁including ▁metric ▁expansion ▁as ▁a ▁feature ▁are : ▁▁ ▁the ▁Cos m ological ▁Princi ple ▁which ▁dem ands ▁that ▁the ▁universe ▁looks ▁the ▁same ▁way ▁in ▁all ▁directions ▁( is otrop ic ) ▁and ▁has ▁roughly ▁the ▁same ▁smooth ▁mixture ▁of ▁material ▁( hom ogeneous ). ▁ ▁the ▁Cop ern ican ▁Princi ple ▁which ▁dem ands ▁that ▁no ▁place ▁in ▁the ▁universe ▁is ▁preferred ▁( that ▁is , ▁the ▁universe ▁has ▁no ▁" start ing ▁point "). ▁ ▁Scient ists ▁have ▁tested ▁carefully ▁whether ▁these ▁assumptions ▁are ▁valid ▁and ▁bor ne ▁out ▁by ▁observation . ▁Observ ational ▁cosm olog ists ▁have ▁discovered ▁evidence ▁– ▁very ▁strong ▁in ▁some ▁cases ▁– ▁that ▁supports ▁these ▁assumptions , ▁and ▁as ▁a ▁result , ▁metric ▁expansion ▁of ▁space ▁is ▁considered ▁by ▁cosm olog ists ▁to ▁be ▁an ▁observed ▁feature ▁on ▁the ▁basis ▁that ▁although ▁we ▁cannot ▁see ▁it ▁directly , ▁scient ists ▁have ▁tested ▁the ▁properties ▁of ▁the ▁universe ▁and ▁observation ▁provides ▁comp elling ▁confirm ation . ▁S ources ▁of ▁this ▁confidence ▁and ▁confirm ation