1 Paradox concerning Quantum mechanics involiving the decay of a particle.
a stationary spinless particle decays into two others with equal mass (the daughters have equal mass) that are traveling in opposite directions at the velocity of light. Now thats the conservation laws covered... except that of spin.
in the later frame the total spin must be zero.... BUT by quantum mechanics Spin is a property that does not exist untill you try to measure it. (this is comming from lecture notes and not thin air before you lot try and flame me)
SO... if you measure the spin of one of the particles and it is spin up, then at that point in time the other particle (which is two times the speed of light multiplyed by time away) instantly takes spin down to create a system of spin zero.
It is known as the Teleportation Paradox.