uct u ations ▁seen ▁in ▁the ▁Cos mic ▁Mic row ave ▁Background . ▁A ▁higher ▁Hub ble ▁constant ▁would ▁imply ▁a ▁smaller ▁characteristic ▁size ▁of ▁C MB ▁fl uct u ations , ▁and ▁vice ▁vers a . ▁The ▁Plan ck ▁collaboration ▁measure ▁the ▁expansion ▁rate ▁this ▁way ▁and ▁determine ▁H 0 ▁= ▁. ▁There ▁is ▁a ▁disag re ement ▁between ▁the ▁two ▁measurements , ▁the ▁distance ▁lad der ▁being ▁model - in dependent ▁and ▁the ▁C MB ▁measurement ▁depending ▁on ▁the ▁fitted ▁model , ▁which ▁hints ▁at ▁new ▁physics ▁beyond ▁our ▁standard ▁cosm ological ▁models . ▁ ▁The ▁Hub ble ▁parameter ▁is ▁not ▁thought ▁to ▁be ▁constant ▁through ▁time . ▁There ▁are ▁dynam ical ▁forces ▁acting ▁on ▁the ▁particles ▁in ▁the ▁universe ▁which ▁affect ▁the ▁expansion ▁rate . ▁It ▁was ▁earlier ▁expected ▁that ▁the ▁Hub ble ▁parameter ▁would ▁be ▁decre asing ▁as ▁time ▁went ▁on ▁due ▁to ▁the ▁influence ▁of ▁gravit ational ▁interactions ▁in ▁the ▁universe , ▁and ▁thus ▁there ▁is ▁an ▁additional ▁observable ▁quantity ▁in ▁the ▁universe ▁called ▁the ▁dec eler ation ▁parameter ▁which ▁cosm olog ists ▁expected ▁to ▁be ▁directly ▁related ▁to ▁the ▁matter ▁density ▁of ▁the ▁universe . ▁Sur pr ising ly , ▁the ▁dec eler ation ▁parameter ▁was ▁measured ▁by ▁two ▁different ▁groups ▁to ▁be ▁less ▁than ▁zero ▁( act ually , ▁consistent ▁with ▁− 1 ) ▁which ▁imp lied ▁that ▁today ▁the ▁Hub ble ▁parameter ▁is ▁conver ging ▁to ▁a ▁constant ▁value ▁as ▁time ▁goes ▁on . ▁Some ▁cosm olog ists ▁have ▁wh ims ically ▁called ▁the ▁effect