Brain Freeze: What is Phase conjugation?is a physical transformation of a wave field where the resulting field has a reversed propagation direction but keeps is amplitudes and phases.

"I don't understand . . .' " said Alice. "It's dreadfully confusing!" 

"That's the effect of living backwards," the Queen said kindly: "it always makes one a little giddy at first- '' "Living backwards!" Alice repeated in great astonishment. "I never heard of such a thing!" -Lewis Carroll