- " 'You see, Marty,' Doc explained in his best lecture mode, 'the continuum has been disrupted, creating a new temporal event sequence resulting in this alternate reality — alternate to us, but reality for everyone else.' / Marty shook his head. He couldn't understand a word. / 'English, Doc,' he requested. / Doc picked up a fallen blackboard and propped it up against the table. Another moment's search, and he had located a piece of chalk. / Doc drew a straight line on the blackboard. / 'Imagine that this line represents time. Here's the present, 1985 —' / He wrote '1985' in the center of the line. / 'The past —' / He wrote 'PAST' to the left. / 'And the future.' / To the right of '1985', he scrawled a big fat 'F'. / 'Now, prior to this point in time' — he pointed again to 1985 — 'somewhere in the past' — he put an 'X' above the line in the past — 'the time line was skewed' — he drew another line, from the bottom of the past, straight down toward the bottom of the blackboard — 'resulting in this alternate 1985. Alternate to you, me and Einstein, but reality for everyone else.' / Marty shook his head. 'I still don't get it, Doc.' "
- —From Back to the Future Part II by Craig Shaw Gardner (quote, page 124)
A blackboard, also sometimes referred to as a chalkboard, was a large, hard, flat black surface which could be written on with chalk.
Emmett Brown found a blackboard in his trashed lab in 1985A, on which he drew a diagram to explain to Marty McFly about the nightmarish alternate reality where they had arrived on returning from 2015 in the DeLorean time machine.
Behind the scenes
- On page 124 of the novelization (see Quote above), the 'X' Doc uses in his diagram to mark the point in the past where the continuum was "skewed" starts off as a lowercase letter, i.e. he put an 'x' above the line in the past. However, the 'X' then suddenly changes to uppercase on page 125, i.e. he drew a long arc, all the way from the 'F' to the 'X' . Bearing in mind that Doc uses uppercase letters throughout the labeling of his diagram, the use of a small 'x' on page 124 would appear to be a misprint. This apparent error has therefore been corrected here.