Hi there, here I have this paradox and hope you can explain. There are 2 charged particles, one is moving at speed v, one is stationary. We know the moving charge gives off a magnetic field which can not exert any force onto the other charge because it does not move. Now assume we stay in a frame which moves at a speed of v/2 (the same direction with the moving charge). We can see the first charge moves at v/2 and the second also moves as v/2 (opposite direction) and so there should be some force exerting on both particles? Thanks for reading and forgive me if my english is not clear enough.