▁in ▁the ▁existence ▁of ▁an ▁a ether . ▁Ein stein ▁later ▁( 1 9 1 8 – 1 9 2 0 ) ▁qualified ▁his ▁position ▁by ▁arg uing ▁that ▁one ▁can ▁speak ▁about ▁a ▁relativ istic ▁a ether , ▁but ▁the ▁" idea ▁of ▁motion " ▁cannot ▁be ▁applied ▁to ▁it . ▁Lor ent z ▁and ▁Po inc ar é ▁had ▁always ▁argued ▁that ▁motion ▁through ▁the ▁a ether ▁was ▁und et ect able . ▁Ein stein ▁used ▁the ▁expression ▁" special ▁theory ▁of ▁relativ ity " ▁in ▁ 1 9 1 5 , ▁to ▁distinguish ▁it ▁from ▁general ▁relativ ity . ▁ ▁Rel ativ istic ▁theories ▁ ▁Gra v itation ▁The ▁first ▁attempt ▁to ▁form ulate ▁a ▁relativ istic ▁theory ▁of ▁grav itation ▁was ▁undert aken ▁by ▁Po inc ar é ▁( 1 9 0 5 ). ▁He ▁tried ▁to ▁modify ▁Newton ' s ▁law ▁of ▁grav itation ▁so ▁that ▁it ▁assumes ▁a ▁Lor ent z - cov ari ant ▁form . ▁He ▁noted ▁that ▁there ▁were ▁many ▁possibilities ▁for ▁a ▁relativ istic ▁law , ▁and ▁he ▁discussed ▁two ▁of ▁them . ▁It ▁was ▁shown ▁by ▁Po inc ar é ▁that ▁the ▁argument ▁of ▁Pierre - Sim on ▁Lap lace , ▁who ▁argued ▁that ▁the ▁speed ▁of ▁gravity ▁is ▁many ▁times ▁faster ▁than ▁the ▁speed ▁of ▁light , ▁is ▁not ▁valid ▁within ▁a ▁relativ istic ▁theory . ▁That ▁is , ▁in ▁a ▁relativ istic ▁theory ▁of ▁grav itation , ▁planet ary ▁or bits ▁are ▁stable ▁even ▁when ▁the ▁speed ▁of ▁gravity ▁is