In Back to the Future, Doc invented time machine in 1985 and he was really excited and little surprised that it worked. But later in movie, Marty goes back and tells young Doc about it.
Why was Doc so surprised about it, when he knew he is inventing it in 1985 since 1955?
But more serious question, when he knew it since 1955, wouldn't this knowledge change the date of first time travel (Make it sooner, because he had lots of information from the future, or even make it later, because he "knew" he will invent so he could stop trying)?
Or why he didn't change the place of meeting with Marty, to prevent attack from Libyans (any events in past could change that moment, when Marty escaped only because the gun has jammed). Is it because he do not want to ruin time-space-continuum?
I know this is not one specific question, more few confused questions, but I hope you understand what is blurry about this movie for me.