Answer: timetravel

AnswerCrossword Clue
TIMETRAVELSci-fi premise
TIMETRAVELThe grandfather paradox implies that it's impossible
TIMETRAVELRevisiting the past?
TIMETRAVEL"Doctor Who" subject
TIMETRAVELSubject of an H.G. Wells novel
TIMETRAVELSci-fi subject
TIMETRAVELMake history, in a way
TIMETRAVEL"Back to the Future" feature
TIMETRAVEL"Back to the Future" subject
TIMETRAVEL"Back to the Future" theme
TIMETRAVELFamiliar science-fiction theme.
TIMETRAVELNot live in the present?