Columns > Published on August 14th, 2013

It's Made Of SCIENCE: The Speed Of Light

Your character is in space, and needs to get somewhere fast. Like, really, really fast. What button do you press?

In Star Wars, you go into hyperspace. In Star Trek, you tell your crew to engage the warp drive. In Dune, you activate the Holtzman engine. With just a little bit of science fiction dust sprinkled on your spaceship, you can get anywhere you need to go as fast as you want with absolutely no consequences.

So does this have a basis in real life? Could we ever develop this kind of technology?

Let's examine this staple of science fiction and see what the deal is with light speed.

Properties of Light

Light moves at roughly 3.0 x 108 meters per second (or 186,000 miles per second), which is really, really fast. You can't even imagine how fast that is. Are you trying? How's that working out for you?

But what if we want to go faster? We, as writers and masters of our fictional worlds, just create an advanced technology and have our space federation build a super pimped-out engine that can go faster than light. We've just built an FTL drive, right?

Well, no, not if you're trying to obey the law of physics as we currently understand them.

Light, it turns out, doesn't really care what seems to make sense to us here on Earth. Instead, the speed of light is the ultimate speed limit. Nothing can go faster than it, and there's a good reason for that. See, the speed of light is the exact same in every reference frame.

What that means is that no matter how fast you are moving, light will always pass you in any direction moving at the speed of light. If you are in a car that is moving forward at near the speed of light, and you turn on the headlamps, then you will see the light (in the form of massless light particles called photons) move forward from the bulbs at the speed of light, even though you are already moving at close to the speed of light. And people who are watching you from Earth will see those exact same photons moving at the speed of light relative to them.

So basically, light always moves at the same speed, no matter the context you're viewing the photons.

Yeah, that might be hard to accept, but don't worry. It took Einstein himself to figure all of this out. It's been put up to pretty rigorous testing by people just as skeptical as you, and the concept of an ultimate speed limit has held pretty tightly. In fact, GPS units have to account for relativity to provide accurate measurements.

So what?

Well, Einstein's theory of relativity messes up some pretty solid preconceptions about our universe.

Let's start with the very fabric of time and space, for starters. Because light always moves at the same speed to all observers, that means that two different people can see the same light photon take two different intervals of time to travel the same path. This is known as time dilation.

Check out this video for a good example:


In a nutshell, the fact that the speed of light is an absolute means that time and distance are relative to you. If I am moving past you, I am technically traveling through time more slowly than you are, depending on how fast I'm moving. Just as well, GPS satellites are moving relative to us on the ground, and therefore are going to drag behind our clocks on Earth by a few nanoseconds per day, which we have to correct to make GPS work accurately.

Everything you see, hear, and experience (the entirety of reality) can only be conveyed as information, and information must travel to your eyes, ears, and so forth somehow. The fastest way it can move is at the speed of light. Since we just established that photons move at a finite (but very fast) speed, that means that information carried by the photon moves at a finite speed, either at or slower than the speed of light.

That means that two events which appear simultaneous for one observer can appear to happen at different times to another observer, since the photons would reach each observer at different points of time. And even better, neither observer would be wrong. The events would be happening simultaneously for one observer, and those same events would be happening at two different times for the second observer. Since time and motion is all relative, there is no "correct context", so both observers would be right.

If there is a zapping sensation in your brain right now, then you'll understand why we consider Einstein one of the greatest scientific minds of all time, since it took a brain like his to figure this stuff out (though, interestingly, he received a Nobel prize for something less dramatic because relativity was considered a bit too radical in the early 1900's).

Light Speed as a Limitation

Basically, the reason you can't go past the speed of light has to do with mathematical barriers, not technological ones. As you approach the speed of light, you increase in "mass" (a term which isn't wholly accurate, but used for simplicity here) but you decrease in length. That means that reaching the speed of light requires you to have infinite "mass", which requires infinite energy to move.

Oh, and your length becomes zero, so that's not good, either.

This means you can't pass the speed of light without Physics Themselves stopping you like some sort of Lovecraftian space highway cop. Even going near the speed of light requires more energy in a single second than our entire planet produces every year. This is the grim reality from which we escape into science fiction books.

Okay, buzzkill, but...

What happens if you do go past the speed of light?

Well, you end up with some mathematically irritating paradoxes. Remember above when I said that the fastest information (perception of existence) can travel is the speed of light? Well, if you go faster than the speed of light, you end up seeing the effect of an event before the cause has occurred. You will see a cup hit the floor before it is dropped, and a person die before they are born.

So, basically, you see time backwards.

Which is cool if you don't think too hard about it, but if you do the math, you end up dividing by zero a lot, and the last guy who did that hasn't been found. Seriously, there's a reason your teachers warned you about that. Don't even try it.

What about tachyons and neutrinos?

So tachyons and neutrinos are two particles theorized to move faster than the speed of light, which would result in a violation of basically this entire article, which would be irritating to me. So let's take a moment to discuss them.

Neutrinos are these super tiny particles that are a byproduct of nuclear reactions (which happen in space all the time). For the record, there is no evidence that these particles move faster than the speed of light. The hubbub came from a mistaken experiment which seemed to record neutrino speed as faster than the speed of light, but later was found to be an equipment error. To my knowledge, the neutrino FTL theory is pretty much dead at this point. So don't let your character reference faster-than-light neutrinos unless he also believes in a flat Earth and trepanation.

Now, while neutrinos are definitely real (and obey special relativity), tachyons are theoretical particles that move faster than light. To date, we have not actually found any of these buggers. They exist mainly as a scientific thought experiment, and manage to tie up some inconsistencies in complicated math we aren't going to explore in this article, but to date, they basically exist as a variable and nothing more.

However, if they do exist, they have the interesting property of always being faster than the speed of light. Read that again. The issues with faster-than-light travel occur when something accelerates faster than the speed of light, but since tachyons (theoretically) are always moving faster than the speed of light, then they never had to accelerate beyond it, and therefore, physics is still technically working the way we think it does. Sure, there are some problems with tachyons technically arriving at places before they departed (as referenced above), but that's a topic for another article.

Is this a problem for my story?

Not. At. All.

See, space is quite big. For instance, to reach the closest star to our own, Proxima Centauri, it would take us somewhere between 76,000 and 81,000 years, using existing technology. That's several thousand human generations. Even if we were moving at the speed of light (an impossibility, remember), it would take us 4.22 years to reach that star.

That's the closest star to us. And since it's a red dwarf that tends to flare up a lot, the likelihood of finding any life out there is not certain.

The absolutely vast distances between interesting things in space is why the speed of light barrier is often ignored or pseudo-scientifically dodged in science fiction stories. It simply takes too long to get to the action if you obey physics.

Hence, the creation of the faster than light engine.

The fact is that unlike other topics which I'll discuss in this series, this scientific inaccuracy is not only accepted, but pretty much necessary for anyone who wants to move their character around the galaxy without having to start a new story each time their character hits the hyperspace button. Even the more serious, realistic shows like the re-imagined Battlestar Galactica, which depicts spaceships that fly realistically and fire bullets instead of lasers, utilizes faster-than-light travel pretty regularly.

You totally can get away with faster-than-light travel, and anyone who complains about it probably doesn't like science fiction anyway.

What are my other options?

If you really delve into the science, you can see some theories out there that argue against the absolute speed limit of light, but you'd need a fairly good physics education to follow them, as will your readers if you try to utilize these theories in your stories. Using complicated equations to justify your technology is probably going to limit your audience to physics graduate students.

Some science fiction writers try to avoid the problem altogether by changing the physics to justify FTL travel. For instance, the warp drive in Star Trek creates a science bubble around the spacecraft that apparently protects it from time dilation while moving at relativistic speeds, which prevents the universe from aging thousands of years for their short hop to the next undiscovered planet.

Other stories prefer having their spaceship enter another dimension where physics work differently, allowing them to basically ignore all of the problems of traveling at the speed of light. It's basically cheating, but as I said, it's better than reading a story that is twenty-seven books of your characters ambling around the spaceship before they leave the solar system.

If you're brave, you can try to accommodate realistic physics in your story. You can put your character on a ship traveling at light speed and allow them to age significantly slower than all of their friends on Earth. When they end up at their destination, years, or even generations could have passed. The Ender's Game series did a pretty good job of exploring the consequences of relativistic travel, even if Card did goof around with the technology a bit.

Too long, didn't read.

Don't talk about accelerating past the speed of light unless you're ignoring physics. It's best to ignore physics if you're trying to get your astronaut to interesting places. Science fiction has pretty much established faster-than-light travel as okay, since it has appeared in all of the sci-fi giants and is really a necessity for anyone trying to move their characters around the galaxy.

But you don't need to be dumb about it. It's a very complicated subject, but even a little research will go a long way to creating a believable method of traveling to your alien planet without breaking math itself.

Do you have an idea for my next science-themed article? I'm taking suggestions! Drop me some topics in the comments, and if I like it, and feel that I either understand or can research it well enough to explain it, your idea can be the next IMOS article. Also, feel free to call me out if you spot an error anywhere; I'd rather have a perfect article than a reputation for being perfect.

About the author

Nathan Scalia earned a BA degree in psychology and considered medical school long enough to realize that he missed reading real books. He then went on to earn a Master's in Library Science and is currently working in a school library. He has written several new articles and columns for LitReactor, served for a time as the site's Community Manager, and can be found in the Writer's Workshop with some frequency.

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