SF Novels That Get Special Relativity All Wrong

I gravitate towards certain SF sub-genres, such as stories featuring relativistic travel. I’ve encountered a fair number of such sub-genre books in which it is clear that the authors did not, emphatically NOT, understand relativity. This article features novels in which authors have wrestled with Mr. Einstein and lost three falls out of three.

As you know, there are two essential foundations of relativity. The first is that the laws of physics are the same everywhere. The second is that the speed of light is invariant regardless of one’s frame of reference. Every single SF novel in which reference is made to time as measured by the ship as “subjective” and time measured by the Earth “objective” is wrong: everyone’s clocks are right, even if they don’t agree with each other.

Now that we are all sufficiently edified, let us proceed…


Robert Heinlein: now there’s a hallowed SFnal name. Whatever else one my think about his books, one must admit that he did not grasp relativity. When he goes into any detail on the matter, it becomes really, really clear that he didn’t understand. Shocking, given that he was born two years (1907) after the publication of Einstein’s seminal paper (1905). I mean, he had time to read up on it!

In Time for the Stars, instantaneous telepathy facilitates communication between twins across interstellar distances. Relativistic travel complicates the issue:

At three-quarters the speed of light he complained that I was drawling, while it seemed to me that he was starting to jabber. At nine-tenths of the speed of light it was close to two for one, but we knew what was wrong now and I talked fast and he talked slow.

The situation should be symmetric: both twins should perceive the other as slowing down. That said, Heinlein has an out here because “instant” communication breaks special relativity. The explanations of just how instantaneous telepathy works makes it clear that in Heinlein’s narrative, there’s a preferred frame of reference. Oh no! Luminiferous ether!

A far more apt example comes from Farmer in the Sky. Farmer does not feature near-light-speed travel, but it does have a remarkable discussion on the subject:

“Mr. Ortega, admitting that you can’t pass the speed of light, what would happen if the Star Rover got up close to the speed of light—and then the Captain suddenly stepped the drive up to about six g and held it there?”

“Why, it would—No, let’s put it this way—” He broke off and grinned; it made him look real young. “See here, kid, don’t ask me questions like that. I’m an engineer with hairy ears, not a mathematical physicist.” He looked thoughtful and added, “Truthfully, I don’t know what would happen, but I would sure give a pretty to find out. Maybe we would find out what the square root of minus one looks like—from the inside.”

The correct answer is “the ship would incrementally approach the speed of light but it would still never reach it or exceed it.” Mr. Ortega is confused here because he’s familiar with how velocities would add up under Newton—which is not how it would work at close to light speed.

According to Newton if something moving at speed u is accelerated by speed v, the result is simple addition: u + v. Einstein (and observation from the real world) says velocities add as (u + v)/(1+uv/c). At velocities much less than light, this produces results close enough to Newton not to matter. But it means one can only approach the speed of light. For example, imagine a starship moving at 0.9 C that is suddenly accelerated by another 0.9 C. Newton says the final velocity would be 1.8 C. Einstein (and experimental results) say the final velocity is ~0.9945 C.


Poul Anderson’s Tau Zero is rightly considered a classic of the Bussard Ramjet genre of science fiction. That said, there are some eyebrow-raising passages of physics tomfoolery, not least of which are the crew members’ convictions regarding their acceleration, and this claim regarding the behavior of the ship sufficiently high speeds:

“I know the figures. We are not as massive as a star. But our energy—I think we could pierce the heart of a sun and not notice.”

From the Leonore Christine’s perspective, they could regard themselves at rest while stars slam into them at a hair less than light-speed, so I am pretty sure whatever emerged on the far side of the star would not be an intact starship. Anderson studied physics in university so I imagine he knew better. This detail is either characterization (such claims come from a crew desperate to believe their struggle means something, not the omniscient narrator) or it’s one of Anderson’s plot-enabling fudges, like the acceleration-compensating fields that can only be generated when passing through the interstellar medium at very high speeds, or the manner in which it’s possible to survive the collapse of a universe by steering one’s ship away from the crunch. Anderson didn’t want to write a book where the ending was “and then everyone died in the interval between one neuron firing and the next.”


Mary Doria Russell’s The Sparrow wasn’t trying to be hard SF, which is just as well. There really is no detail concerning near-light-speed travel (aside from the inability to reach or exceed the speed of light) that the novel gets right: relativistic effects become noticeable at much smaller relative speeds than they should, and the time it takes her starships to reach Alpha Centauri is wrong as well.


Donald Moffitt was part of a cohort of SF writers first published by Del Rey that I think of as “Niven-like.” That is, I suspect that Del Rey published them in the belief that readers who liked Niven’s fiction would like Moffitt’s (and Hogan’s and McCollum’s and others). Worked for me! I snapped up The Jupiter Theft on sight. Moffitt made a curious mistake in The Jupiter Theft: he used strictly Newtonian equations to calculate the product of acceleration, while applying relativistic calculations to the result. As a consequence, he seems to have firmly believed that because 300,000,000 m/s ÷ 10 m/s/s = 30,000,000 or almost exactly a year, space craft accelerating at one gravity could get arbitrarily close to the speed of light in just a year. Because velocities don’t quite work that way, the actual answer is closer to 0.77 C.

(Moffitt’s confusion about physics blinded me to the effort he put into making his aliens alien.)

Moffitt’s orientalist space-opera duology, The Mechanical Sky, delivered further confusion. The starfarers of the future know that for some reason spacecraft accelerating away from the Solar System mysteriously vanish at the 40 LY. It turns out that there’s a simple explanation: as spacecraft approach the speed of light, they gain mass and 40 LY happens to be where a spacecraft accelerating at 1-g gains so much mass it collapses into a black hole! To quote the Justice League’s Flash in a quite different context, there are so many reasons why that shouldn’t have worked, not least of which is that of course the rockets are at rest with respect to themselves: from their perspective, their clocks are normal, their measured dimensions are the same as they ever were; it’s the rest of the universe that is subject to relativity’s curious (and experimentally verified) effects.


It’s a curious thing that Special Relativity has been around for most than a century and General Relativity almost as long, but most of us still have trouble wrapping our minds around it (and some remarkable people refuse to accept them as useful models at all). Still, I’d rather see SF authors try and fail than never try at all.

In the words of Wikipedia editor TexasAndroid, prolific book reviewer and perennial Darwin Award nominee James Davis Nicoll is of “questionable notability.” His work has appeared in Publishers Weekly and Romantic Times as well as on his own websites, James Nicoll Reviews and Young People Read Old SFF (where he is assisted by editor Karen Lofstrom and web person Adrienne L. Travis). He is surprisingly flammable.




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