Relativitic momentum p =γ m v Consider explosion happens with two particles of equal mass m moving in opposite directions with the same speed. So, the total momentum before and after explosion is zero and conserved. However, if I try to calculated the total momentum before and after explosion as veiwed from another intial frame of reference moving with speed v, they are not conserved! Before explosion, p = (m+m)v After explosion, p = p1 + p2 = γ1 m v1 + γ2 m v2 v1 is the velocity of m1 as viewed from another frame v2 is the velocity of m2 as viewed from another frame γ1 is 1/(1-v1^2/c^2)^0.5 γ2 is 1/(1-v2^2/c^2)^0.5 My calculation shows the total linear momentum does NOT conserved! Why? Thank you.