light speed broadcasts I’m a writer. I'm working on a story. It’s sold actually, but they want some changes and I’m trying to figure out the science..
IDEA:
A  distant planet picks up broadcasts from Earth, so the inhabitants have some knowledge of us, and know that life is out there. A "man" on the alien planet gets part of his consciousness encoded into a light beam that is sent out into space.
When it hits earth -It is able to project itself and appear to be human. When the light fades the man vanishes, leaving a message that he is long dead.  (It's a love story.) But the question is what broadcasts would he have received  time wise. His knowledge of earth would be limited, ending at a certain time...  
This is the end/explanation.
Thank you in advance for your help!
“ My people developed a holographic beam so powerful it could be projected through space. Through light-years. It is more advanced than anything on Earth, so advanced that some actual particles of my being were intertwined with the particles of light being projected. So it was like
I was actually here, next to you, talking to you,
laughing with you. But I was not. I am not.
“When we sent the beam of light traveling into
space my particles were woven into it, not all of them, of course. But enough particles of my consciousness were intertwined with the particles of light so that I could interact with anyone I discovered. ...So that I could learn more about the world we’d previously only
known through television broadcasts. ..
“I traveled in a spaceship made of light. Now that
the light has died so have the particles of my
consciousness that were interwoven with the beam.... The real 'me, ' the corporeal 'me,' died --- HOW MANY? light years ago."
Long ago, men went to sea. And women waited for them, peering out into black waters, searching for a tiny speck of light on the horizon. Now I too wait, looking out into the vast blackness of space, searching for my love, my heart, HOW MANY? light-years dead.
Thanks for any help with this. Elizabeth.
 A: Assuming that the turn-around time is zero, the holographic consciousness will be 2N years out of date when it arrives, where N is the distance in light years between earth and the alien system. So, if the system is 10 light years from us, our lover will be 20 years out of date when he (she?) arrives. So, for instance, if the holograph arrives today, it must have left the alien system 10 years ago, in 2005. At that time the latest broadcast received from earth would have left earth in 1995. 
It is perfectly reasonable (for techie types) to refer to duration in terms of light years, but this assumes that all travel takes place at the speed of light, which is clearly appropriate for your story.
A: I know this is not entirely what your story-plot might be going for but the talk of weaving the consciousness with some of the transmitted beams reminds me a bit of the entanglement that you have in quantum mechanics.
I don't know how 'techie' the story is supposed to be but you could imagine the message sent being some advanced version of the EPR paradox or Bell experiment. This would not allow for faster than light communication, but never the less the alien planet would have a record of the holographic? conversation taking place on earth.
Good luck! Hope you get what you are looking for ;)
