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On Writing Science Fiction: The Speed of Light

First in my series on writing science fiction

September 12 2017
September 12 2017

I like writing space opera. Space opera (for me) requires interstellar space travel. Any meaningful interstellar space travel requires that the characters be able to travel between points in the universe that are hundreds of millions or even billions of light years apart in the course of several hours. That means they must go faster than the speed of light. A lot faster. Hundreds of millions or even billions of times faster.

But I read an article recently on NPR where it discussed being realistic in science fiction. That is, the story would take place in a world bound by our current understanding of science. That would preclude not only faster-than-light travel, but travel at any meaningful fraction of the speed of light.

The speed of light is approximately 186,000 miles (300,000 km) per second, or about 670 million miles per hour. It is considered to be an absolute that cannot be exceeded (as was the sound barrier at one time). The reason it can’t be exceeded is that as an object approaches the speed of light, it’s mass approaches infinity, and therefore the energy required to move it approaches infinity. Even at large percentages of the speed of light, the energy required to move an object becomes so high as to make it impossible.

So, how fast can we really go? My “research” on Google suggests that the fastest spacecraft we’ve made so far can go at about 20,000 miles per hour. Maybe slightly more, but the difference is negligible for the distances involved.

But I want to write a story where the characters go to planets in other galaxies all across the universe. So, what’s the problem? The problem is the vast size of the universe.

The nearest galaxy outside ours is Sagittarius Dwarf Spheroidal Galaxy, which is about 80,000 light years from Earth. (Dwarf? It’s 10,000 light years across.)

A light year is the distance light travels in a year, or about six trillion miles. When we look at this galaxy, the light that reaches our eyes left there 80,000 years ago. That is, if we were able to go at the speed of light, it would take us 80,000 years to get there.

Okay, so why not stay in our own galaxy. The galactic core is 27,000 light years from Earth. The nearest star is four light years. The diameter of the Milky Way is between 100,000 and 120,000 light years (although I’ve seen estimates of up to 180,000 light years). Our situation, then, is no better.

Even if we wanted to stay inside our solar system, distances are vast. It would take about 150 days to get to Mars, given our current technology.

There’s one other problem: communications. A radio signal, which is a form of light, travels (you guessed it) at the speed of light. You can see the problem with sending a message to Earth from a galaxy 80,000 light years away.

This all points to the fundamental question for the sci-fi writer. Unless we are willing to break the laws of physics to the extent it borders on magic, we are limited to the immediate neighborhood of Earth. And remember: not only are Earthlings bound by these limitations, so are aliens. So, a story sticking to the limits of physics as they are known today would necessarily exclude inter-stellar travel by anyone, including aliens. Therefore, in the absence of faster-than-light travel and communication, we can only tell a story about Earthlings interacting with Earthlings within our solar system, or on a spaceship that takes hundreds or thousands of years to get anywhere outside it.

Consider one of the books mentioned in the NPR article: Aurora, by Kim Stanley Robinson. It deals with a spaceship that goes off from Earth to the star Tau Centi, which is a relatively close twelve light years from Earth. The trip is to take 160 years. According to my calculation, that means the ship would need to go about 51 million miles per hour (which is still only 0.076 times the speed of light). Even that vastly exceeds the bounds of what we can do now. At 20,000 mph, the trip would take over 410,000 years.

Therefore, if no travel at many times the speed of light, no space opera. No Star Wars, no Dune, no Star Trek, no Predator, etc. And no aliens, outside of those originating in our solar system.

In Star Trek, no one had any trouble believing that there were special crystals that made the construction of a warp engine possible. In Dune, the Guild was able to fold space because of the spice. How can their authors get away with that? It’s because the reader wants to be able to travel to other planets, and they want to do it without being in hibernation for thousands of years.

All the author has to do is to “lampshade” the issue. That is, to shine a light on the fact that they have to go thousands or millions of times the speed of light, and give some explanation as to how it was done. You don’t have to be specific. You can’t. All Frank Herbert had to do was to say that the spice modified the Guild members so they could fold space with their minds, and bada-bing, bada-boom. Faster-than-light travel. You bought it, and I bought it. It was creative, and it was believable. Magic? Maybe, but it was presented not as magic, but as a phenomenon for which there is a “scientific” explanation.

Another problem with going at the speed of light is time dilation. Time goes slower for the person traveling at light speed than it does for those standing still. My solution, and the solution of most authors I'm aware of, ignore it. To me, it opens a real can of worms that would be impossible to deal with in a story.

To me, keeping science fiction Earthbound is less interesting. It becomes merely a predictor of technology, and what will happen on Earth in the future. It can, admittedly, be quite interesting, such as is the case with BladerunnerVoyage to the Bottom of the Sea, and Fantastic Voyage. But doesn’t it open up a whole new world of possibilities if we allow our minds to leap the light barrier?

Here is an interesting, although annoying, video on the relative time it takes spaceships from science fiction to go certain distances.


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