Back to the Future Confusion

I watched all three parts of the Back to the Future series of movies over the last week and it left me with a burning question: How do Marty and the Doc ever meet in the first place? Obviously their lives become intertwined with all the time travel. We see Doc meet Marty for the first time in 1955 when Doc is 1955-Doc and Marty is 1985-Marty, but when does Marty first meet Doc? What is the nature of their relationship such that Marty is the first person to witness time travel? Or that Marty can just wander into Doc's house? Despite three movies of wandering back and forth over a 130 year period Spielberg gives no insight into this relationship. Some possibilities posed by me:

1. Marty works for the Doc (this is perhaps the least likely since Marty shows little to no scientific acumen)
2. They are somehow related or Doc is a family friend.
   
3. Doc contacted Marty sometime in the 80's either on pretense of work or whatever. Probably not "Hey Marty, you don't know me, but I met you in 1955!"
4. Fate brings them together in some manner.

There doesn't seem to be much evidence for any of these hypotheses, but it's something that certainly bothered me throughout the series.

In other news, I got a fancy new computer this week. It's a desktop and Ian made it custom for me. =)

Registration for spring quarter is next week and I'm planning to take 3rd year Arabic, Media Arabic, sociolinguistics, and writing. I still have to take a writing class which is pretty dumb since I've taken several in my college existance and I took 2 AP writing/lit classes in high school. Oh well. It looks like the textbooks for it are graphic novels, which is strange but possibly good. I remain somewhat undecided on this account.