Sticking to the Speed Limit by Starbrat (printer friendly) discuss (15 posts)

The vast majority of SF in games, books, TV and cinema has often assumed some arcane but essentially simple method to ignore the universal speed limit; the speed of light. Stemming from initial disappointment regarding the natures of our nearby worlds, SF writers had to look farther afield to set their space adventures. While this approach has proven very popular, there is something to be said for sticking to the speed limit.

So, What's all the Fuss About?

As described in the "Starships" accessory, many rather odd things happen to a body the faster it travels. Perhaps the most important change for a spacecraft is mass increase. As velocity increases, the mass of a spacecraft rapidly becomes unmanageable. Eventually, the spacecraft's engines cannot accelerate the vessel any more (though, depending upon the engines' performance, the spacecraft may mass anything from that of a small moon to a planet, star, galaxy or even a galactic cluster before this limit is reached!). This effect is what renders the speed of light unnattainable. No matter what form of propulsion is used (even a distorted spacetime metric such as an induction drive), engine performance will eventually degrade as the vessel's mass increases. To achieve lightspeed itself, the vessel's mass would become infinite and would therefore require an infinite amount of energy to accelerate. Of course, such a horrendously massive object would have long since destroyed any destinations worth visiting by its own gravity!

The Uses of Relativity

Apart from setting a speed limit on the Universe, relativistic effects can actually be quite useful. Length contraction and time dilation can seriously distort the way the crew perceives time and distance, allowing starfarers to undertake the kind of journey that even crew of the USS Enterprise would balk at.

One little-noted point regarding relativistic effects is that they work in both directions. Just as the spacecraft appears to grow shorter in its axis of travel, so the universe at large appears to become more crowded, as the distance between objects appears to compress. This is how time dilation effects translate to the crew of the starship. Also, just as the actions of the crew appear to slow down as time dilation takes effect, so does the view from the rear of the starship.

This second effect has a far-reaching implication for star travel and strategy. It works because the speed of light is a constant. As a spacecraft speeds up, light rays reaching it from behind become stretched as they try to catch up with the rapidly-fleeing starship. On the other hand, images from in fromt of the ship appear to speed up as the vessel rams into the forward images, forcing them to compress in a kind of natural time-lapse effect.

This effect is also seen from outside the starship. Observers watching a starship leave Earth for Alpha Centauri would see the ship begin to slow down, as its hind-images become more rarified by the rapid travel of the ship. Assuming a very high cruising speed of 0.999c and a very high acceleration (say 60g), the trip would appear to take about eight-and-a-half years (Just over four and a quarter years for the ship to make the journey, and another four and a quarter for the image of the arriving ship to wend its way back to Earth). From Alpha Centauri, however, it's a very different story. From in front of the starship, the vessel is running right behind its own images at it pushes toward the speed of its own light. The result is a kind of fast-forward effect, causing the ship to appear to streak across the intervening space in just under ten weeks (the time experienced by the crew).

As a result, a fast starship gives its destination little in the way of warning, making surprise a powerful weapon in a warship's arsenal.

Effects on Your Campaign

So, how does enforcing the lightspeed limit affect a SF campaign? For starters, even if very rapid relativistic flight is available, no interstellar distance can be called trivial. Interstellar flights begin to resemble the Age of Exploration's intercontinental journeys, great voyages of discovery and adventure. Each planetary system, in only intermittent contact with its neighbours, will develop its own distinct personality and forms of government. While interstellar empires are still possible, regional government becomes much more important, resembling the European empires of the eighteenth century. This allows crises to develop in all sorts of interesting ways before the universe at large can get involved. Heroes trapped in a war zone may have to sweat it out for a while before the next starship arrives. Even if they're lucky enough to have a ship of their own, there will be no more quick escapes into hyperspace or whatever. A determined pursuer will be able to keep harrying them for as long as the most sadistic GM desires, creating many opportunities for adventure and drama.

Events may move more slowly in a sub-light campaign, but they will move with crushing force. Also, when then heroes, replete with praise and a fat paycheque, leave a system for new horizons, events will keep moving on without them. It may be a bit disconcerting to return a few "months" later, to find out that in the intervening years the lieutenents of the defeated nemesis have regained power and are after the heroes' blood! It allows drama and adventure to follow the heroes without the plausibility-stretching "new crisis every episode" syndrome that can affect games as well as TV shows. The lightspeed limit allows events time to ferment, with starfaring heroes acting as the catalyst.

Other effects are more aesthetic than strictly game-related, but aesthetics are an important facet of any worthwhile campaign. By confining spacflight to relativistic or sub-relativistic speeds, the magnificent emptiness of interstellar (or even interplanetary) space can be appreciated for once. When there's no way to get to Vulcan in time for next week's episode, the heroes will appreciate just how alone they are, strengthening party-member bonds and helping them to rely on each other rather than on the outside world for a quick fix. In fact, it seems likely that a certin clannishness would be part and parcel of the mentality of far-roaming space travellers.

But What About Planets?

If travel between plaetary systems is difficult (or even impossible), how can the GM keep coming up with new and exciting adventure locales? Well, adventure writers of the last couple of centuries have had little difficulty, even when confined to a single planet. Add the sorts of exotic locale that our own system provides (such as the ten-kilometre ice-cliffs of Mimas, the nitrogen geysers of Triton, the possible deep-freeze ethane oceans of Titan, the great canyons of Mars's Noctis Labyrinthus and the subterranean oceans of Jupiter's larger moons) together with the dazzling variety of possible artificial environments, and it becomes plain that even a relatively modest solar system can provide a gamut of roleplaying environments without the heroes having to visit the same place twice!

Also, it allows the GM time to devote some attention to developing his or her worlds, creating a more vivid environment for the players to interact with. Given that some games can end up creating planets that seem all-too alike, the opportunity to devote more attention to world-design is another major bonus.

Relativistic Effects Table

Rather than recalculating relativistic terms from the "Starships" accessory, below is a quick-reference table listing several velocities and their effects. As you can see, relativistic efects only become extreme factors when the vessel's velocity exceeds 0.7 c. I call this point the "Relativity point", since spaccraft travelling faster than 0.7c provide what feels like FTL flight to their crew.

Velocity (c)------Length and Time---------------Mass


© Mark Peoples 2001.

Discussion forum


(9) in But... by darkwolf on 02-03-2008

(4) in Dissenting opinion? by Corvus on 01-09-2004

(2) in Eurrrgh by Starbrat on 01-06-2001


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