- " '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.
Dr. 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.
At the Institute of Future Technology (I.F.T.) in 1991, Doc had drawn on a blackboard a schematic diagram of the 8-passenger DeLorean, which he showed to each party of volunteers who would be traveling in a journey across the space-time continuum.
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.