“Consider: a single light-year is an inconceivable abyss. Denumerable but inconceivable. At an ordinary speed – say, a reasonable pace for a car in megalopolitan traffic, two kilometers per minute – you would consume almost nine million years in crossing it. And in Sol’s neighborhood, the stars averaged some nine light-years part. Beta Virginis was thirty-two distant. Nevertheless, such spaces could be conquered.”
In “Tau Zero” by Poul Anderson.
Yeah I'm aware of the twin paradox and how Special Relativity alone doesn't account for the returning twin being younger; at the time I remember wondering specifically whether one of the main criticism of Tau zero (i.e. that the crew of the ship should observe the universe as being slower relative to them while they're accelerating, not sped up as it is in the book) was on the nose. Not that most people think that special relativity is simple, but in fact it is even trickier than is apparent the first time you meet it. The crucial point to remember is that what you actually see is very different from what is happening "in the observer's frame of reference" as the jargon has it, because you have to allow for the time that light takes to get to you, which adds a whole extra layer of distortions they don't tell you about in your first relativity course. If you take that into account, special relativity has no problem completely accounting for the twin paradox, for instance. In fact in Tau Zero the speed of light is still an uncrossable barrier - as it would be; the point is the effects of time dilation, and as the drive keeps working and the momentum increases, so the dilation effect increases. Since he was trying to discuss the physics, might help to get that bit right. Most "paradoxes" in Special Relativity can be resolved by just doing the Lorentz transformations. The implications of SF time travel are different. Time Travel in a deterministic universe (Terminator 1). People have a lot of problems with this, partly because they assume everything started out in a timeline without time travel. If it is a deterministic universe, the time traveler was always going to travel back in time and his actions were always going to happen. This imposed self-consistency would exclude a large numbers of possible timelines and require very specific actions, but it's not all that strange. Time travel in a not self-consistent universe (Terminator 2 or back to the future). Yep. Quite straightforward. Time travel in a seemingly self-consistent universe that might not really be- See many worlds interpretation of quantum mechanics. Add time travel.
Think about it for a while. Fun.
What bothered me at the time was not the twin paradox though; what bugged me was the pushing the spaceship to light speed. Besides the fact that it would take infinite energy to push mass "at" the speed of light, let alone surpass it, which Einstein proved is impossible; if you reached it, for an observer your time would stop and for you, your time, distance to everything would be zero, you would see the whole future life of the universe unfold instantaneously.
But SF does not have eyes to see, eyes lacking elsewhere; the insights come from physics, and the writers can have no more insight than that. In general, they have less. So, despite a final paragraph obviously written more with an eye for an ending than with an eye on content, it is no good looking to SF to tell you what the Universe is up to; much of it is sub-O level, much of it fantasy, not SF and the remainder is both hard to find and usually badly written (very few people who spend years studying math and physics turn out to be good writers - it has been known, but it is rare).
Perhaps the larger point is that looking at others to explain things for you is a weak idea (in fact doomed); better to learn and understand for yourself.
When SF authors develop the courage to stop recycling their Sunday school primers, perhaps the genre will prove the Jesuits wrong: "give me a child until the age of seven, and I will show you the man!"
SF = Speculative Fiction.