Prior to this point in time, somewhere in the past, the timeline skewed into this tangent creating an alternate 1985. Alternate to you, me and Einstein, but reality for everyone else.
— Dr. Emmett Brown (Christopher Lloyd)
16 seconds sound clip from the Back to the Future Part II movie soundboard.
You can hear this line at 00:52:41.083 in the Blu-ray version of the movie.
