yeah, still another 5 years to go to invent it bum. (see below)
Sourced from another forum:
Doc was originally going to travel 25 years into the future. Which of course would be this year. However, he never set the date on the time circuits.
What happened was:
* Doc was showing Marty how the machine worked. He punched in dates like: 25/12/0000 (to witness the birth of christ) and 4/7/1776 (to see the signing of the declaration of independance) and "a red letter date in the history of science... November 5th, 1955" which of course was the day the doc had a vision of the flux capacitor.
* At this time, he realised he didnt pack enough plutonium to get back FROM the future and got out of the delorean.
* When out of the car, he saw the Libyan terrorists and was shot.
* Marty jumped into the car to get away from them with the time circuits still set to 5/11/1955.
* Marty then went back in time, almost hooked up with his mother, invented the skateboard and dumped a load of shit into biffs car and successfully predicted when/where lightining would strike.
At the end of the movie, Doc changed his destination from 2010 (25 years) to 2015.... because it fell in sync with the 30 years Marty travelled and because it was a nice round number.
Sorry for the confusion