Grand Unified FTL 1: Introduction

Posted: 2024-06-25
Word Count: 1770
Tags: space rpg

Table of Contents

This series of articles is a Work In Progress. Links to future articles will be broken until they’re finished.

WARNING: this article may contain numbers.

Science fiction authors (and some scientists) have proposed several methods to allow humans and (as far as we know fictional) aliens to traverse the vast distances between stars. In this article I will categorize the various methods, provide simple but specific ways to handle each method, and at least sketch out system-independent mechanics that game designers and tinkerers can incorporate into tabletop RPGs and hobby games.

A Note on Units

The discussion below uses units and abbreviations from the International System of Units (SI):

SI Meaning Equivalent
d day 86400 s
g gram 0.001 kg; about 0.0353 ounces
h hour 3600 s
kg kilogram 1000 g; about 2.204623 pounds
km kilometer 1000 m; about 0.62137 miles, 1093.6 yards, or 3280.8 ft.
ky kiloyear 1000 y, i.e. a millennium.
m meter about 1.0936 yards, 3.2808 ft, or 39.37 in.
min minute 60 s
s second something about vibrations of cesium clocks
t(P) Planck time1 5.39 x 10-44 s
y year 365.25 days
a/b a per b e.g. “m/s” means meters per second.

Some Depressing Physics

To motivate the discussion I’m going to rattle off some pertinent science. This isn’t simply to show off the degree I didn’t get but to point out that using real-world physics and hard numbers we won’t be going to the stars any time soon.

Stars Are Far Away

In 1905 Einstein demonstrated that the fastest anything can travel in this universe is the speed of light (c or C), or about 3 x 108 m/s2. This is damned inconvenient.

Light takes 8.3 minutes to travel one Astronomical Unit (AU), 149,597,870.7 km, the average distance from the Sun to the Earth. The distance from our sun to the nearest stars can be measured in light-years (LY), or the distance light travels in a year3. Scientists sometimes also measure interstellar distances in parsecs (pc)4; 1 pc is about 3.26 LY. Having said that, we’ll continue to use LY.

It’s Too Hard To Get To Them

Oh but it gets worse. (And they say Economics is the dismal science.)

As an object, e.g. a ship full of people, travels at a significant fraction of the speed of light5, the following happens:

  1. The object gains mass, so it’s harder to accelerate to higher speeds.
  2. Time relative to the object slows down; when a minute passes in the object, in the outside world more than a minute passes, sometimes much more.

These effects grow not merely exponentially but asymptotically. That is, accelerating an object close to the speed of light may take all the energy in the Universe and then some, while the crew remains virtually frozen in time.

The only way light itself gets around this problem is that light has no mass. It has energy, or else it wouldn’t exist at all, but multiplying zero by anything is zero.6

So How Do We Do It?

Scientists have come up with unlikely but plausible scenarios to cross interstellar space at slower than light (STL) speeds using vaguely reasonable amounts of energy. Examples from hard7 science fiction include:

All these ideas have other problems, like propulsion for the long trip, shielding humans from cosmic rays, and not getting taken out by interstellar debris the ship will inevitably run into at a velocity of a few thousand meters per second.

But we’re writing fiction, so we cheat.

Specifically, every other science fiction author has used a fictional device to get around these limits. Maybe there’s some way to skip outside the universe and skip back in light-years away. Maybe there’s some effect like “quantum tunneling” on an Einsteinian scale so that it doesn’t take infinite energy to cross the stars in a reasonable time frame. Maybe there’s a “warp drive” or something that simply ignores the speed limit.

Varieties of FTL

Fictional FTL mechanisms boil down to these options:

  1. Hyperspace: The ship enters a type or realm of space where distances in normal space don’t apply, and exits again light-years away. In some cases the ship uses a pre-existing “hyperspace gate”; larger ships can sometimes create their own gates. Examples include Andromeda’s slipstream drive, Babylon 5, Cowboy Bebop (for interplanetary travel), Crest of the Stars’s Plane Space, Doctor Who’s Time Vortex (for time and space), The Expanse’s Ring Network, Ann Leckie’s Imperial Radsch series (Ancillary Justice and following), and Stargate SG-1’s various spaceships.

  2. Jump: Once the ship engages a “jump drive” the ship and crew instantly teleports from one place to another, experiencing little if any time in between. Examples include classic stories from Isaac Asimov and others, Battlestar Galactica (2004-2009), Event Horizon (possibly), Star Trek: Discovery’s spore drive8, The Stars My Destination’s psionic talent of Jaunting, and the Traveller RPG (influenced by Asimov et al.).

  3. Portal: The ship simply flies through a “portal” that connects two arbitrarily distant regions of space. The portal may remain open for anyone to use or require some device to activate it or initiate travel. Likewise the portal may connect only two fixed regions of space or each portal entrance can connect to any other endpoint. Authors usually explain these portals as mysterious natural phenomena, technology from vanished aliens, or established technology invented in a dimly remembered past. Examples include Charles Stross’s Accelerando, the Coriolis RPG, the Diaspora RPG (as far as I can tell), the Hyperion novel series, and the eponymous Stargate (for people and very narrow ships).

  4. Teletransport: A sending station transmits a person as a data stream across the stars, either their entire body9 or only their mind10, and the receiving station must assemble a body at the other end.11 Often this transmission must obey the light-speed limit (or not), but at least the data stream experiences no transit time (or does it?). Examples of whole-body teleportation include Doctor Who’s transmats, Stargate SG-1’s explanation of Stargates, the souped-up transporters in the 2009 Star Trek, and the short story “Think Like a Dinosaur”. Examples of the mental version include Altered Carbon and Neptunes Brood.

  5. Warp: The ship warps space-time around it to avoid the light-speed limit, but still travels (partially?) in normal space. Star Trek is the classic example, although ships in Crest of the Stars create “warp bubbles” to travel “short” distances and fight.

Some franchises mix and match elements from each option. Star Wars uses Hyperspace, but ships accelerate to light speed like a Warp Drive and rely on complex calculations involving known planetary masses and “hyperspace paths” like a classic Jump Drive.

Tomorrow Problems

Despite my review of SI Units, some scientific questions I’m not going to address, because they’re hard.


We first consider Astrogation.

  1. The shortest interval theoretically possible in physics. ↩︎

  2. Specifically 299,792,458 m/s or about 186,000 miles per second or 671,000,000 miles per hour. ↩︎

  3. About 9.46 1012 km. ↩︎

  4. About 3.0 x 1016 m. Which is a measure of distance not time. I’m looking at you, Han Solo. ↩︎

  5. I think it’s 20% to 30%, but don’t quote me. ↩︎

  6. Early 20th century writer E. E. “Doc” Smith wrote novels in which starships canceled inertia or something … which would get you to the speed of light but not beyond it. Despite that, a lot of space opera owes a debt to him; AFAIK he invented the whole notion of ships fighting with rays and defending themselves with force fields. (But I prefer the much more imaginative and slyly humorous Cordwainer Smith.) ↩︎

  7. By which I mean SF that sticks to known science, or at least gray areas where science has no definitive answer (like xenobiology). ↩︎

  8. Subspace mushrooms? Seriously? ↩︎

  9. Which raises the question of what to do with the original. “Think Like a Dinosaur” takes the infamous “transporter problem” to its logical and in this case bloody conclusion. ↩︎

  10. This presumes a technology to backup a brain like a computer and restore it in a different body, like the cortical stacks of Altered Carbon or the wholly artificial life forms in Neptune’s Brood↩︎

  11. H. P. Lovecraft’s “The Whisperer in Darkness” introduces a gruesome early variation in which beings capable of traveling across the stars take only a human’s brain in a canister that keeps them (barely) alive. The cannister gets no body at the end, only crude sensory and speaking apparatus to converse with their patrons/captors. ↩︎