Time travel has been a favorite science fiction theme ever since it was first used in H.G. Wells's trailblazing novel The Time Machine. But not everything it describes is science fiction: traveling forward in time, for example, is a proven fact. Einstein's theory of relativity predicts that an observer moving relative to Earth can leap into Earth's future, and the effect has been confirmed using atomic clocks. Dramatic time warps require speeds close to that of light, which is possible in principle but would take a major feat of engineering, not to mention a lot of money. Going back in time is far more problematic. Relativity does not rule out an observer being able to make a journey through space-time and return to their past. But all scenarios so far discussed require exotic circumstances.
It is pointed in the passage that The Time Machine by H.G. Wells ____.
was to a large extent inspired by Einstein's theory of relativity
was the first novel to deal with the idea of time travel
is the only early work of science fiction that still remains popular
is still regarded as a standard reference for time travel studies
focuses on travel into the past rather than into the future
According to the passage, going back in time ____.
has been feasible ever since Einstein formulated the theory of relativity
may not be impossible but presents a great many difficulties
is completely contradicted by the theory of relativity
requires speeds that are greater than the speed of light
was an idea originally put forward by Einstein
The passage makes the point that is possible to travel into Earth's future ____.
though this has not been verified by atomic clocks
and indeed this has already been achieved
at reasonably attainable speeds
if Einstein's theory of relativity is found to be true
but technically and financially it is still not possible