A single fact from scientific theory can legitimize the far-fetched. Take the nature of time. We move forward in time at twenty-four hours a day and sixty minutes an hour. ‘We are all time travellers… We are all stuck on the same train, and for practical purposes, it never speeds up, slows down, or goes backwards’ (Time Travel in Theory and Practice, Love (2013) from The Time Traveller’s Almanac.) Or does it? Absolute time is a theory of the past; gravity slows down time’s progress and travelling at high-speed triggers the contrary.
Part 3 of Through the Portal looks at The Twins Paradox and Robert Heinlein's 1956 novel, Time for the Stars.
