His motives for volunteering lie somewhere on the 'continuum' between charitable and self-serving.
a 'continuum' of temperatures ranging from very cold to very hot
(..) I can't imagine Hell being much worse. DOC: Einie. I'm sorry, boy. The lab is an awful, awful mess. Attaboy. Obviously, the time continuum has been disrupted... ...creating this new temporal event sequence... ...resulting in this alternate reality. - English, Doc. (..)1989 Back to the Future Part II
(..) put her into shock, and she'd pass out... ...or two, the encounter could create a time paradox... ...and cause a chain reaction that would unravel... ...the space-time continuum and destroy the entire universe! Granted, that's a worst-case scenario. The destruction might be localized, (..)1989 Back to the Future Part II