Like Dirac's equation, Maxwell's wave equation for light also has two solutions, the so-called "retarded solution" that describes a wave traveling forward in time and the "advanced solution" that describes a light wave traveling backward in time. Both of these waves travel at the same speed-the speed of light in vacuum-- but in opposite temporal directions. The retarded wave travels in the normal direction -- from past to future -- while the advanced wave goes the other way -- from the future into the past...
When we stand in the dark and look at a star a hundred light years away, not only have the retarded light waves from the star been traveling for a hundred years to reach our eyes, but the advanced waves generated by absorption processes within our eyes have reached a hundred years into the past, completing the transaction that permitted the star to shine in our direction.
This means that the star must have "known", in a sense, that you were going to be standing there before it bothered to send that photon on its way all those hundreds (or even billions) of years ago. In other words our notion of the passage of time is an illusion, that past and future exist simultaneously as coordinates on the fourth axis of Space-Time.
