Suppose I could go contact him back into time. What would I tell him?
I could tell him about his beautiful granddaughters.
I could tell him that his Red Sox won another world series in 2007 but some things don't change, it's the Yankees who are reigning champs.
I could tell him about a device in my pocket called an "iPhone" that lets me contact anyone, access nearly all public information and it plays music and movies too. A big improvement over the Sony Walkman.
I could tell him about how easily we can search for the most trivial information. I learned that he wrote a review article when I was just a baby, that the house he grew up in was torn down and replaced with the Marshfield city hall, and that he died just about the same time that JR was shot.
I could tell him the answer to the biggest mystery of his generation: FBI Agent Mark Felt was Deep Throat.
But most of I would tell my father that taking one children's aspirin every day reduces the risk of heart attacks and maybe, just maybe, I'd be telling him these things in person.