▁in ▁motion , ▁obey ing ▁certain ▁laws ▁of ▁nature ▁which ▁science ▁see ks ▁to ▁understand . ▁For ▁this ▁reason ▁the ▁most ▁fundamental ▁science ▁is ▁generally ▁understood ▁to ▁be ▁" physics " — the ▁name ▁for ▁which ▁is ▁still ▁recogn izable ▁as ▁meaning ▁that ▁it ▁is ▁the ▁" stud y ▁of ▁nature ". ▁ ▁M atter ▁is ▁commonly ▁defined ▁as ▁the ▁subst ance ▁of ▁which ▁physical ▁objects ▁are ▁composed . ▁It ▁constit utes ▁the ▁observable ▁universe . ▁The ▁visible ▁components ▁of ▁the ▁universe ▁are ▁now ▁believed ▁to ▁compose ▁only ▁ 4 . 9 ▁percent ▁of ▁the ▁total ▁mass . ▁The ▁remainder ▁is ▁believed ▁to ▁consist ▁of ▁ 2 6 . 8 ▁percent ▁cold ▁dark ▁matter ▁and ▁ 6 8 . 3 ▁percent ▁dark ▁energy . ▁The ▁exact ▁arrangement ▁of ▁these ▁components ▁is ▁still ▁unknown ▁and ▁is ▁under ▁int ensive ▁investigation ▁by ▁phys ic ists . ▁ ▁The ▁behaviour ▁of ▁matter ▁and ▁energy ▁throughout ▁the ▁observable ▁universe ▁appears ▁to ▁follow ▁well - defined ▁physical ▁laws . ▁These ▁laws ▁have ▁been ▁employed ▁to ▁produce ▁cosm ological ▁models ▁that ▁successfully ▁explain ▁the ▁structure ▁and ▁the ▁evolution ▁of ▁the ▁universe ▁we ▁can ▁observe . ▁The ▁mathematical ▁expressions ▁of ▁the ▁laws ▁of ▁physics ▁employ ▁a ▁set ▁of ▁twenty ▁physical ▁constants ▁that ▁appear ▁to ▁be ▁static ▁across ▁the ▁observable ▁universe . ▁The ▁values ▁of ▁these ▁constants ▁have ▁been ▁carefully ▁measured , ▁but ▁the ▁reason ▁for ▁their ▁specific ▁values ▁remains ▁a ▁mystery . ▁ ▁Bey ond ▁Earth ▁ ▁Out er ▁space , ▁also ▁simply ▁called ▁space , ▁refers ▁to ▁the ▁relatively