so loj invariant huab hwm coj
Rau ib qho khoom hauv ib lub xeev twg, coj inertial system K kom tus kwv nyob ruaj ruaj rau inertial system K, tom qab ntawd qhov ntau ntawm cov khoom ntsuas hauv qhov inertial system K hu ua" so mass" ;. Qhov seem loj ntawm tib yam khoom yog Lorentz invariant. Qhov ntau ntawm cov khoom pom nyob rau hauv lwm cov sib dhos inertial ntawm cov kwv tij txheeb ze rau nws cov lus tsa suab yog hu ua" tsab ntawv pawg".