Wherever I have read, the conservation of momentum is a universal truth. This is the basis, as I undertsand it, to the mass equation: m = m0/SQRT(1 - v2/c2) in which m0 = the mass in the rest frame and m is the mass in the moving frame relative to the rest frame moving at v. The idea behind it, as I understand it, that in order to conserve momentum, one must increase the mass to keep the mv product the same, as the "moving frame" is time dilated and v is functionally less than the v in the rest frame. Does this automatically happen?. The interesting part about this is that the v in the moving frame is "slowed down" by time dilation yet the v is perpendicular to the path of the moving frame. I guess time dilation must occur in all three axes (x, y, z) as it would be impossible for an object to exist at one time in x and "simultaneously" other times in y and z.