This is to understand about the mathematics and possible limitations of the concept of preferred frames in BM and why entanglement couldn't use one. Supposed you have a cruise missile sent out from earth to a distant planet travelling at 0.99999 the speed of light. 30 Seconds after sending it out.. you got order to cancel and self destruct the missile. But you can't use even light speed signal to catch it. Now you use emergency tachyon beam to contact the missile at a certain v > c with respect to a preferred frame common to earth and the missile. But in the frame of reference of the missile. The space is contracted between it and the distant planet so it takes only say 3 seconds to reach it. Now when you use tachyons travelling with respect to the preferred frame (not with respect to earth). How does the preferred frame synchronize your 30 seconds with the missile when it takes only 3 seconds for it to reach the target? I understand the tachyons should travel with respect to the preferred frame. This is because if it travels with respect to earth. It can't reach the missile (or too late) or can even receive the signal before it sents out (by the missile sending back instantaneously to earth's past). But in a preferred frame, not only can the earth not receive it before it sends out. But it might be able to catch the missile halfway before it reaches the target, can it? Of course I don't believe in tachyons. This is just to work out the math to prove preferred frames are never feasible in BM and entanglement and I have been thinking of this for over a day. Thank you.