Every age has characteristic inventions that change the world. In the 19^th century it was the steam engine and the train. For the 20^th, electric and gasoline power, aircraft, nuclear weapons, even ventures into space. Today, the planet is awash with electronic business, chatter and virtual-reality entertainment so brilliant that the division between real and simulated is hard to discern. But one new idea from the 19^th century has failed, so far, to enter reality—time travel, using machines to turn the time dimension into a two-way highway. Will it come true, as foreseen in science fiction? Might we expect visits to and from the future, sooner than from space? That is the Time Machine Hypothesis, examined here by futurist Damien Broderick, an award-winning writer and theorist of the genre of the future. Broderick homes in on the topic through the lens of science as well as fiction, exploring some fifty different time-travel scenarios and conundrums found in the science fiction literature and film.