▁tw in ▁acceler ates ▁and ▁changes ▁direction , ▁so ▁L ange vin ▁could ▁show ▁that ▁the ▁symmetry ▁is ▁broken ▁and ▁the ▁acceler ated ▁tw in ▁is ▁younger . ▁However , ▁L ange vin ▁himself ▁interpreted ▁this ▁as ▁a ▁hint ▁as ▁to ▁the ▁existence ▁of ▁an ▁a ether . ▁Although ▁L ange vin ' s ▁explanation ▁is ▁still ▁accepted ▁by ▁some , ▁his ▁conclus ions ▁regarding ▁the ▁a ether ▁were ▁not ▁generally ▁accepted . ▁La ue ▁( 1 9 1 3 ) ▁pointed ▁out ▁that ▁any ▁acceleration ▁can ▁be ▁made ▁arbitr arily ▁small ▁in ▁relation ▁to ▁the ▁in ert ial ▁motion ▁of ▁the ▁tw in , ▁and ▁that ▁the ▁real ▁explanation ▁is ▁that ▁one ▁tw in ▁is ▁at ▁rest ▁in ▁two ▁different ▁in ert ial ▁frames ▁during ▁his ▁journey , ▁while ▁the ▁other ▁tw in ▁is ▁at ▁rest ▁in ▁a ▁single ▁in ert ial ▁frame . ▁La ue ▁was ▁also ▁the ▁first ▁to ▁analyze ▁the ▁situation ▁based ▁on ▁M ink owski ' s ▁spac etime ▁model ▁for ▁special ▁relativ ity   – ▁showing ▁how ▁the ▁world ▁lines ▁of ▁in ert ial ly ▁moving ▁bodies ▁maxim ize ▁the ▁proper ▁time ▁el apsed ▁between ▁two ▁events . ▁ ▁Acc eler ation ▁Ein stein ▁( 1 9 0 8 ) ▁tried   – ▁as ▁a ▁pre lim inary ▁in ▁the ▁framework ▁of ▁special ▁relativ ity   – ▁also ▁to ▁include ▁acceler ated ▁frames ▁within ▁the ▁relativ ity ▁principle . ▁In ▁the ▁course ▁of ▁this ▁attempt ▁he ▁recognized ▁that ▁for ▁any ▁single ▁moment ▁of ▁acceleration ▁of ▁a ▁body